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• Asynchronous vs Synchronous vs Threading in an iPhone App

  - by Coocoo4Cocoa

  I'm in the design stage for an app which will utilize a REST web service and sort of have a dilemma in as far as using asynchronous vs synchronous vs threading. Here's the scenario. Say you have three options to drill down into, each one having its own REST-based resource. I can either lazily load each one with a synchronous request, but that'll block the UI and prevent the user from hitting a back navigation button while data is retrieved. This case applies almost anywhere except for when your application requires a login screen. I can't see any reason to use synchronous HTTP requests vs asynchronous because of that reason alone. The only time it makes sense is to have a worker thread make your synchronous request, and notify the main thread when the request is done. This will prevent the block. The question then is bench marking your code and seeing which has more overhead, a threaded synchronous request or an asynchronous request. The problem with asynchronous requests is you need to either setup a smart notification or delegate system as you can have multiple requests for multiple resources happening at any given time. The other problem with them is if I have a class, say a singleton which is handling all of my data, I can't use asynchronous requests in a getter method. Meaning the following won't go: - (NSArray *)users { if(users == nil) users = do_async_request // NO GOOD return users; } whereas the following: - (NSArray *)users { if(users == nil) users == do_sync_request // OK. return users; } You also might have priority. What I mean by priority is if you look at Apple's Mail application on the iPhone, you'll notice they first suck down your entire POP/IMAP tree before making a second request to retrieve the first 2 lines (the default) of your message. I suppose my question to you experts is this. When are you using asynchronous, synchronous, threads -- and when are you using either async/sync in a thread? What kind of delegation system do you have setup to know what to do when a async request completes? Are you prioritizing your async requests? There's a gamut of solutions to this all too common problem. It's simple to hack something out. The problem is, I don't want to hack and I want to have something that's simple and easy to maintain.

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• Core-Data + AFNetworking + UI Updating (Responsiveness)

  - by Mustafa

  Here's the scenario: I'm writing a DownloadManager, that allows the user to download, pause, cancel, download all, and pause all. The DownloadManager is a singleton, and uses AFNetworking to download files. It has it's own private managed object context, so that user can freely use other parts of the application (by adding, editing, deleting) core-data objects. I have a core-data entity DownloadInfo that stores the download information i.e. fileURL, fileSize, bytesRead, etc. The DownloadManager updates the download progress in DownloadInfo (one for each file). I have a DownloadManagerViewController which uses NSFetchedResultsController to show the download status to the user. This download view controller is using the main managed object context. Now let's say that I have 20 files in the download queue. And let's say that only 3 concurrent downloads are allowed. The download manager should download the file, and show the download progress. Problem: The DownloadInfo objects are being updated by the DownloadManager at a very high rate. The DownloadManagerViewController (responsible for showing the download progress) is updating the list using NSFetchedResultsControllerDelegate methods. The result is that a lot is happening in the main queue and application has very poor responsiveness. How can I fix this? How can I make the application responsive, while showing the download progress? I don't know how else to communicate that the download status between DownloadManager and DownloadManagerViewController. Is there another/ a better way to do this? I don't want to use main managed object context in my DownloadManager, for reasons mentioned above. Note, that the DownloadManager is using AFNetworking which is handling the requests asynchronously, but eventually the DownloadInfo objects are updated in the main thread (as a result of the callback methods). Maybe there's a way to handle the downloads and status update operations in a background thread? but how? How will I communicate between the main thread and the background thread i.e. how will I tell the background thread to queue another file for download? Thanks.

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• Optimizing Haskell code

  - by Masse

  I'm trying to learn Haskell and after an article in reddit about Markov text chains, I decided to implement Markov text generation first in Python and now in Haskell. However I noticed that my python implementation is way faster than the Haskell version, even Haskell is compiled to native code. I am wondering what I should do to make the Haskell code run faster and for now I believe it's so much slower because of using Data.Map instead of hashmaps, but I'm not sure I'll post the Python code and Haskell as well. With the same data, Python takes around 3 seconds and Haskell is closer to 16 seconds. It comes without saying that I'll take any constructive criticism :). import random import re import cPickle class Markov: def __init__(self, filenames): self.filenames = filenames self.cache = self.train(self.readfiles()) picklefd = open("dump", "w") cPickle.dump(self.cache, picklefd) picklefd.close() def train(self, text): splitted = re.findall(r"(\w+|[.!?',])", text) print "Total of %d splitted words" % (len(splitted)) cache = {} for i in xrange(len(splitted)-2): pair = (splitted[i], splitted[i+1]) followup = splitted[i+2] if pair in cache: if followup not in cache[pair]: cache[pair][followup] = 1 else: cache[pair][followup] += 1 else: cache[pair] = {followup: 1} return cache def readfiles(self): data = "" for filename in self.filenames: fd = open(filename) data += fd.read() fd.close() return data def concat(self, words): sentence = "" for word in words: if word in "'\",?!:;.": sentence = sentence[0:-1] + word + " " else: sentence += word + " " return sentence def pickword(self, words): temp = [(k, words[k]) for k in words] results = [] for (word, n) in temp: results.append(word) if n > 1: for i in xrange(n-1): results.append(word) return random.choice(results) def gentext(self, words): allwords = [k for k in self.cache] (first, second) = random.choice(filter(lambda (a,b): a.istitle(), [k for k in self.cache])) sentence = [first, second] while len(sentence) < words or sentence[-1] is not ".": current = (sentence[-2], sentence[-1]) if current in self.cache: followup = self.pickword(self.cache[current]) sentence.append(followup) else: print "Wasn't able to. Breaking" break print self.concat(sentence) Markov(["76.txt"]) -- module Markov ( train , fox ) where import Debug.Trace import qualified Data.Map as M import qualified System.Random as R import qualified Data.ByteString.Char8 as B type Database = M.Map (B.ByteString, B.ByteString) (M.Map B.ByteString Int) train :: [B.ByteString] -> Database train (x:y:[]) = M.empty train (x:y:z:xs) = let l = train (y:z:xs) in M.insertWith' (\new old -> M.insertWith' (+) z 1 old) (x, y) (M.singleton z 1) `seq` l main = do contents <- B.readFile "76.txt" print $ train $ B.words contents fox="The quick brown fox jumps over the brown fox who is slow jumps over the brown fox who is dead."

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• iPhone OS: KVO: Why is my Observer only getting notified at applicationDidfinishLaunching

  - by nickthedude

  I am basically trying to implement an achievement tracking setup in my app. I have a managedObjectModel class called StatTracker to keep track of all sorts of stats and I want my Achievement tracking class to be notified when those stats change so I can check them against a value and see if the user has earned an achievement. I've tried to impliment KVO and I think I'm pretty close to making it happen but the problem I'm running into is this: So in the appDelegate i have an Ivar for my Achievement tracker class, I attach it as an observer to a property value of my statTracker core data entity in the applicationDidFinishLaunching method. I know its making the connection because I've been able to trigger a UIAlert in my AchievementTracker instance, and I've put several log statements that should be triggered whenever the value on the StatTracker's property changes. the log statement appears only once at the application launch. I'm wondering if I'm missing something in the whole object lifecycle scheme of things, I just don't understand why the observer stops getting notified of changes after the applicationDidFinishLaunching method has run. Does it have something to do with the scope of the AchievementTracker reference or more likely the reference to my core data StatTracker is going away once that method finishes up. I guess I'm not sure the right place to place these if that is the case. Would love some help. Here is the code where I add the observer in my appDidFinishLaunching method: [[CoreDataSingleton sharedCoreDataSingleton] incrementStatTrackerStat:@"timesLaunched"]; achievementsObserver = [[AchievementTracker alloc] init]; StatTracker *object = nil; object = [[[CoreDataSingleton sharedCoreDataSingleton] getStatTracker] objectAtIndex:0]; NSLog(@"%@",[object description]); [[CoreDataSingleton sharedCoreDataSingleton] addObserver:achievementsObserver toStat:@"refreshCount"]; here is the code in my core data singleton: -(void) addObserver:(id)observer toStat:(NSString *) statToObserve { NSLog(@"observer added"); NSArray *array = [[NSArray alloc] init]; array = [self getStatTracker]; [[array objectAtIndex:0] addObserver:observer forKeyPath:statToObserve options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL]; } and my AchievementTracker: - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { NSLog(@"achievemnt hit"); //NSLog("%@", [change description]); if ([keyPath isEqual:@"refreshCount"] && ((NSInteger)[change valueForKey:@"NSKeyValueObservingOptionOld"] == 60) ) { NSLog(@"achievemnt hit inside"); UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"title" message:@"achievement unlocked" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:nil]; [alert show]; } }

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• How build my own Application Setting

  - by adisembiring

  I want to build a ApplicationSetting for my application. The ApplicationSetting can be stored in a properties file or in a database table. The settings are stored in key-value pairs. E.g. ftp.host = blade ftp.username = dummy ftp.pass = pass content.row_pagination = 20 content.title = How to train your dragon. I have designed it as follows: Application settings reader: interface IApplicationSettingReader { read(); } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { List<AppSettingEntity> listEntity = appSettingsDao.findAll(); Map<String, String> map = new HaspMap<String, String>(); foreach (AppSettingEntity entity : listEntity) { map.put(entity.getConfigName(), entity.getConfigValue()); } return new AppSettings(map); } } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { //read from some properties file return new AppSettings(map); } } Application settings class: AppSettings { private static AppSettings instance; private Map map; Public AppSettings(Map map) { this.map = map; } public static AppSettings getInstance() { if (instance == null) { throw new RuntimeException("Object not configure yet"); } return instance; } public static configure(IApplicationSettingReader reader) { instance = reader.read(); } public String getFtpSetting(String param) { return map.get("ftp." + param); } public String getContentSetting(String param) { return map.get("content." + param); } } Test class: AppSettingsTest { IApplicationSettingReader reader; @Before public void setUp() throws Exception { reader = new DatabaseApplicationSettingReader(); } @Test public void getContentSetting_should_get_content_title() { AppSettings.configure(reader); Instance settings = AppSettings.getInstance(); String title = settings.getContentSetting("title"); assertNotNull(title); Sysout(title); } } My questions are: Can you give your opinion about my code, is there something wrong? I configure my application setting once, while the application start, I configure the application setting with appropriate reader (DbReader or PropertiesReader), I make it singleton. The problem is, when some user edit the database or file directly to database or file, I can't get the changed values. Now, I want to implement something like ApplicationSettingChangeListener. So if the data changes, I will refresh my application settings. Do you have any suggestions how this can be implemented?

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• MKMap showing detail of annotations

  - by yeohchan

  I have encountered a problem of populating the description for each annotation. Each annotation works, but there is somehow an area when trying to click on it. Here is the code. the one in bold is the one that has the problem. -(void)viewDidLoad{ FlickrFetcher *fetcher=[FlickrFetcher sharedInstance]; NSArray *rec=[fetcher recentGeoTaggedPhotos]; for(NSDictionary *dic in rec){ NSLog(@"%@",dic); NSDictionary *string = [fetcher locationForPhotoID:[dic objectForKey:@"id"]]; double latitude = [[string objectForKey:@"latitude"] doubleValue]; double longitude = [[string objectForKey:@"longitude"]doubleValue]; if(latitude !=0 && latitude != 0 ){ CLLocationCoordinate2D coordinate1 = { latitude,longitude }; **NSDictionary *adress=[NSDictionary dictionaryWithObjectsAndKeys:[dic objectForKey:@"owner"],[dic objectForKey:@"title"],nil];** MKPlacemark *anArea=[[MKPlacemark alloc]initWithCoordinate:coordinate1 addressDictionary:adress]; [mapView addAnnotation:anArea]; } } } Here is what the Flickr class does: #import <Foundation/Foundation.h> #define TEST_HIGH_NETWORK_LATENCY 0 typedef enum { FlickrFetcherPhotoFormatSquare, FlickrFetcherPhotoFormatLarge } FlickrFetcherPhotoFormat; @interface FlickrFetcher : NSObject { NSManagedObjectModel *managedObjectModel; NSManagedObjectContext *managedObjectContext; NSPersistentStoreCoordinator *persistentStoreCoordinator; } // Returns the 'singleton' instance of this class + (id)sharedInstance; // // Local Database Access // // Checks to see if any database exists on disk - (BOOL)databaseExists; // Returns the NSManagedObjectContext for inserting and fetching objects into the store - (NSManagedObjectContext *)managedObjectContext; // Returns an array of objects already in the database for the given Entity Name and Predicate - (NSArray *)fetchManagedObjectsForEntity:(NSString*)entityName withPredicate:(NSPredicate*)predicate; // Returns an NSFetchedResultsController for a given Entity Name and Predicate - (NSFetchedResultsController *)fetchedResultsControllerForEntity:(NSString*)entityName withPredicate:(NSPredicate*)predicate; // // Flickr API access // NOTE: these are blocking methods that wrap the Flickr API and wait on the results of a network request // // Returns an array of Flickr photo information for photos with the given tag - (NSArray *)photosForUser:(NSString *)username; // Returns an array of the most recent geo-tagged photos - (NSArray *)recentGeoTaggedPhotos; // Returns a dictionary of user info for a given user ID. individual photos contain a user ID keyed as "owner" - (NSString *)usernameForUserID:(NSString *)userID; // Returns the photo for a given server, id and secret - (NSData *)dataForPhotoID:(NSString *)photoID fromFarm:(NSString *)farm onServer:(NSString *)server withSecret:(NSString *)secret inFormat:(FlickrFetcherPhotoFormat)format; // Returns a dictionary containing the latitue and longitude where the photo was taken (among other information) - (NSDictionary *)locationForPhotoID:(NSString *)photoID; @end

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• References between Spring beans when using a NameSpaceHandler

  - by teabot

  I'm trying to use a Spring context namespace to build some existing configuration objects in an application. I have defined a context and pretty much have if working satisfactorily - however, I'd like one bean defined by my namespace to implicitly reference another: Consider the class named 'Node': public Class Node { private String aField; private Node nextNode; public Node(String aField, Node nextNode) { ... } Now in my Spring context I have something like so: <myns:container> <myns:node aField="nodeOne"/> <myns:node aField="nodeTwo"/> </myns:container> Now I'd like nodeOne.getNode() == nodeTwo to be true. So that nodeOne.getNode() and nodeTwo refer to the same bean instance. These are pretty much the relevant parts I have in my AbstractBeanDefinitionParser: public AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) { ... BeanDefinitionBuilder containerFactory = BeanDefinitionBuilder.rootBeanDefinition(ContainerFactoryBean.class); List<BeanDefinition> containerNodes = Lists.newArrayList(); String previousNodeBeanName; // iterate backwards over the 'node' elements for (int i = nodeElements.size() - 1; i >= 0; --i) { BeanDefinitionBuilder node = BeanDefinitionBuilder.rootBeanDefinition(Node.class); node.setScope(BeanDefinition.SCOPE_SINGLETON); String nodeField = nodeElements.getAttribute("aField"); node.addConstructorArgValue(nodeField); if (previousNodeBeanName != null) { node.addConstructorArgValue(new RuntimeBeanReference(previousNodeBeanName)); } else { node.addConstructorArgValue(null); } BeanDefinition nodeDefinition = node.getBeanDefinition(); previousNodeBeanName = "inner-node-" + nodeField; parserContext.getRegistry().registerBeanDefinition(previousNodeBeanName, nodeDefinition); containerNodes.add(node); } containerFactory.addPropertyValue("nodes", containerNodes); } When the application context is created my Node instances are created and recognized as singletons. Furthermore, the nextNode property is populated with a Node instance with the previous nodes configuration - however, it isn't the same instance. If I output a log message in Node's constructor I see two instances created for each node bean definition. I can think of a few workarounds myself but I'm keen to use the existing model. So can anyone tell me how I can pass these runtime bean references so that I get the correct singleton behaviour for my Node instances?

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• Good working habits to observe in project development?

  - by Will Marcouiller

  As my development experience grows, I see fit to stick to best practices from here and there to build somehow my own working practices while observing the conventions, etc. I'm currently working on a project which my goals is to graduate the security access model from an environment's Active Directory to another environment's automatically. I don't know for any of you, but as far as I'm concerned, I meet some real difficulties sticking to only one way, then develop. I mean, I learn something new everyday while visiting SO, and recently wanted to get acquainted with generics. On the other hand, I better know the Façade pattern which proved to be very practical in transactional programming in process systems. This seems to be less practical for desktop application as there are plenty of variables to consider in a desktop application that you don't have to care in transactional programming, as you're playing only with information data. As for my current project, I have: Groups; Organizational Units; Users. Which are all considered an entry in the Active Directory. This points out to be a good candidate for generics, as also approached this way by Bart de Smett's Linq to AD on CodePlex. He has a DirectorySource<T>, and to manage let's say groups, then he instantiate a source with the proper type: var groups = new DirectorySource<Group>(); This seems to be very a good way of doing. Despite, I seem to go from one pattern to another and I don't seem to be able to strictly stick to one. While I'm aware that one must not stay with only one way of doing, since each pattern statisfies certain advantages, while also illustrating disadvantages under some usage conditions, I seem to want to develop with both patterns having a singleton Façade class with the underlying factories which represent the sub systems: GroupsFactory; UsersFactory; OrganizationalUnitsFactory. Each of the factories offers the possible operations for their respective entity (group, user, OU). To make a very long story short, I often have plenty of ideas while developping and this causes me some trouble, as I go from an idea to another feeling completely lost after a while. Yet I understand the advantages and disavantages, I have no trouble choosing from one pattern to another depending on the situation. Nevertheless, when it comes to programming itself, if I'm not part of a team, I feel sometimes like I can't do anything good. That is, because I can't stand not doing something "perfect" the first time. The role I play within the project is both: the project manager and the programmer. I am more comfortable in the project manager role, architectural role, analytical role than the developer's. Has any of you some good habbits to observe in project development? Thanks to you all! =)

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• Ninject with Object Initializers and LINQ

  - by Alexander Kahoun

  I'm new to Ninject so what I'm trying may not even be possible but I wanted to ask. I free-handed the below so there may be typos. Let's say I have an interface: public interface IPerson { string FirstName { get; set; } string LastName { get; set;} string GetFullName(); } And a concrete: public class Person : IPerson { public string FirstName { get; set; } public string LastName { get; set; } public string GetFullName() { return String.Concat(FirstName, " ", LastName); } } What I'm used to doing is something like this when I'm retrieving data from arrays or xml: public IEnumerable<IPerson> GetPeople(string xml) { XElement persons = XElement.Parse(xml); IEnumerable<IPerson> people = ( from person in persons.Descendants("person") select new Person { FirstName = person.Attribute("FName").Value, LastName = person.Attribute("LName").Value }).ToList(); return people; } I don't want to tightly couple the concrete to the interface in this manner. I haven't been able to find any information in regards to using Ninject with LINQ to Objects or with object initializers. I may be looking in the wrong places, but I've been searching for a day now with no luck at all. I was contemplating putting the kernel into an singleton instance and seeing if that would work, but I'm not sure that it will plus I've heard that passing your kernel around is a bad thing. I'm trying to implement this in a class library currently. If this is not possible, does anyone have any examples or suggestions as to what the best practice is in this case? Thanks in advance for the help. EDIT: Based on some of the answers I feel I should clarify. Yes, the example above appears short lived but it was simply an example of one piece that I was trying to do. Let's give a bigger picture. Say instead of XML I am gathering all my data through a 3rd party web service and I'm creating an interface for it, the data could be a defined object in the wsdl or it could sometimes be an xml string. IPerson could be used for both the Person object and a User object. I will be doing this inside of a separate class library, because it needs to be portable and will be used in other projects, and handing it to an MVC3 Web Application and the objects will be used in javascript as well. I appreciate all the input so far.

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• Multi-threaded Pooled Allocators

  - by Darren Engwirda

  I'm having some issues using pooled memory allocators for std::list objects in a multi-threaded application. The part of the code I'm concerned with runs each thread function in isolation (i.e. there is no communication or synchronization between threads) and therefore I'd like to setup separate memory pools for each thread, where each pool is not thread-safe (and hence fast). I've tried using a shared thread-safe singleton memory pool and found the performance to be poor, as expected. This is a heavily simplified version of the type of thing I'm trying to do. A lot has been included in a pseudo-code kind of way, sorry if it's confusing. /* The thread functor - one instance of MAKE_QUADTREE created for each thread */ class make_quadtree { private: /* A non-thread-safe memory pool for int linked list items, let's say that it's * something along the lines of BOOST::OBJECT_POOL */ pooled_allocator<int> item_pool; /* The problem! - a local class that would be constructed within each std::list as the * allocator but really just delegates to ITEM_POOL */ class local_alloc { public : //!! I understand that I can't access ITEM_POOL from within a nested class like //!! this, that's really my question - can I get something along these lines to //!! work?? pointer allocate (size_t n) { return ( item_pool.allocate(n) ); } }; public : make_quadtree (): item_pool() // only construct 1 instance of ITEM_POOL per // MAKE_QUADTREE object { /* The kind of data structures - vectors of linked lists * The idea is that all of the linked lists should share a local pooled allocator */ std::vector<std::list<int, local_alloc>> lists; /* The actual operations - too complicated to show, but in general: * * - The vector LISTS is grown as a quadtree is built, it's size is the number of * quadtree "boxes" * * - Each element of LISTS (each linked list) represents the ID's of items * contained within each quadtree box (say they're xy points), as the quadtree * is grown a lot of ID pop/push-ing between lists occurs, hence the memory pool * is important for performance */ } }; So really my problem is that I'd like to have one memory pool instance per thread functor instance, but within each thread functor share the pool between multiple std::list objects.

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• .NET XmlSerializer fails with List<T>

  - by Redshirt

  I'm using a singleton class to save all my settings info. It's first utilized by calling Settings.ValidateSettings(@"C:\MyApp"). The problem I'm having is that 'List Contacts' is causing the xmlserializer to fail to write the settings file, or to load said settings. If I comment out the List<T> then I have no problems saving/loading the xml file. What am I doing wrong? // The actual settings to save public class MyAppSettings { public bool FirstLoad { get; set; } public string VehicleFolderName { get; set; } public string ContactFolderName { get; set; } public List<ContactInfo> Contacts { get { if (contacts == null) contacts = new List<ContactInfo>(); return contacts; } set { contacts = value; } } private List<ContactInfo> contacts; } // The class in which the settings are manipulated public static class Settings { public static string SettingPath; private static MyAppSettings instance; public static MyAppSettings Instance { get { if (instance == null) instance = new MyAppSettings(); return instance; } set { instance = value; } } public static void InitializeSettings(string path) { SettingPath = Path.GetFullPath(path + "\\MyApp.xml"); if (File.Exists(SettingPath)) { LoadSettings(); } else { Instance.FirstLoad = true; Instance.VehicleFolderName = "Cars"; Instance.ContactFolderName = "Contacts"; SaveSettingsFile(); } } // load the settings from the xml file private static void LoadSettings() { XmlSerializer ser = new XmlSerializer(typeof(MyAppSettings)); TextReader reader = new StreamReader(SettingPath); Instance = (MyAppSettings)ser.Deserialize(reader); reader.Close(); } // Save the settings to the xml file public static void SaveSettingsFile() { XmlSerializer ser = new XmlSerializer(typeof(MyAppSettings)); TextWriter writer = new StreamWriter(SettingPath); ser.Serialize(writer, Settings.Instance); writer.Close(); } public static bool ValidateSettings(string initialFolder) { try { Settings.InitializeSettings(initialFolder); } catch (Exception e) { return false; } // Do some validation logic here return true; } } // A utility class to contain each contact detail public class ContactInfo { public string ContactID; public string Name; public string PhoneNumber; public string Details; public bool Active; public int SortOrder; }

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• One Controller is Sometimes Bound Twice with Ninject

  - by Dusda

  I have the following NinjectModule, where we bind our repositories and business objects: /// <summary> /// Used by Ninject to bind interface contracts to concrete types. /// </summary> public class ServiceModule : NinjectModule { /// <summary> /// Loads this instance. /// </summary> public override void Load() { //bindings here. //Bind<IMyInterface>().To<MyImplementation>(); Bind<IUserRepository>().To<SqlUserRepository>(); Bind<IHomeRepository>().To<SqlHomeRepository>(); Bind<IPhotoRepository>().To<SqlPhotoRepository>(); //and so on //business objects Bind<IUser>().To<Data.User>(); Bind<IHome>().To<Data.Home>(); Bind<IPhoto>().To<Data.Photo>(); //and so on } } And here are the relevant overrides from our Global.asax, where we inherit from NinjectHttpApplication in order to integrate it with Asp.Net Mvc (The module lies in a separate dll called Thing.Web.Configuration): protected override void OnApplicationStarted() { base.OnApplicationStarted(); //routes and areas AreaRegistration.RegisterAllAreas(); RegisterRoutes(RouteTable.Routes); //Initializes a singleton that must reference this HttpApplication class, //in order to provide the Ninject Kernel to the rest of Thing.Web. This //is necessary because there are a few instances (currently Membership) //that require manual dependency injection. NinjectKernel.Instance = new NinjectKernel(this); //view model factory. NinjectKernel.Instance.Kernel.Bind<IModelFactory>().To<MasterModelFactory>(); } protected override NinjectControllerFactory CreateControllerFactory() { return base.CreateControllerFactory(); } protected override Ninject.IKernel CreateKernel() { var kernel = new StandardKernel(); kernel.Load("Thing.Web.Configuration.dll"); return kernel; } Now, everything works great, with one exception: For some reason, sometimes Ninject will bind the PhotoController twice. This leads to an ActivationException, because Ninject can't discern which PhotoController I want. This causes all requests for thumbnails and other user images on the site to fail. Here is the PhotoController in it's entirety: public class PhotoController : Controller { public PhotoController() { } public ActionResult Index(string id) { var dir = Server.MapPath("~/" + ConfigurationManager.AppSettings["UserPhotos"]); var path = Path.Combine(dir, id); return base.File(path, "image/jpeg"); } } Every controller works in exactly the same way, but for some reason the PhotoController gets double-bound. Even then, it only happens occasionally (either when re-building the solution, or on staging/production when the app pool kicks in). Once this happens, it continues to happen until I redeploy without changing anything. So...what's up with that?

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• [NHibernate and ASP.NET MVC] How can I implement a robust session-per-request pattern in my project,

  - by Guillaume Gervais

  I'm currently building an ASP.NET MVC project, with NHibernate as its persistance layer. For now, some functionnalities have been implemented, but only use local NHibernate sessions: each method that accessed the database (read or write) needs to instanciate its own NHibernate session, with the "using()" directive. The problem is that I want to leverage NHibernate's Lazy-Loading capabilities to improve the performance of my project. This implies an open NHibernate session per request until the view is rendered. Furthermore, simultaneous request must be supported (multiple Sessions at the same time). How can I achieve that as cleanly as possible? I searched the Web a little bit and learned about the session-per-request pattern. Most of the implementations I saw used some sort of Http* (HttpContext, etc.) object to store the session. Also, using the Application_BeginRequest/Application_EndRequest functions is complicated, since they get fired for each HTTP request (aspx files, css files, js files, etc.), when I only want to instanciate a session once per request. The concern that I have is that I don't want my views or controllers to have access to NHibernate sessions (or, more generally, NHibernate namespaces and code). That means that I do not want to handle sessions at the controller level nor the view one. I have a few options in mind. Which one seems the best ? Use interceptors (like in GRAILS) that get triggered before and after the controller action. These would open and close sessions/transactions. Is it possible in the ASP.NET MVC world? Use the CurrentSessionContext Singleton provided by NHibernate in a Web context. Using this page as an example, I think this is quite promising, but that still requires filters at the controller level. Use the HttpContext.Current.Items to store the request session. This, coupled with a few lines of code in Global.asax.cs, can easily provide me with a session on the request level. However, it means that dependencies will be injected between NHibernate and my views (HttpContext). Thank you very much!

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• SQLiteOpenHelper getWritableDatabse() fails with no Exception

  - by Michal K

  I have a very strange problem. It only shows from time to time, on several devices. Can't seem to reproduce it when I want, but had it so many times, that I think I know where I get it. So I have a Loader which connects to sqlite through a singleton SQLiteOpenHelper: try{ Log.i(TAG, "Get details offline / db helper: "+DatabaseHelper.getInstance(getContext())); SQLiteDatabase db=DatabaseHelper.getInstance(this.getContext()).getWritableDatabase(); Log.i(TAG, "Get details offline / db: "+db); //doing some work on the db //... } catch(SQLiteException e){ e.printStackTrace(); return null; } catch(Exception e){ e.printStackTrace(); return null; //trying everything to grab some exception or whatever } My SQLIteOpenHelper looks something like this: public class DatabaseHelper extends SQLiteOpenHelper { private static DatabaseHelper mInstance = null; private static Context mCxt; public static DatabaseHelper getInstance(Context cxt) { //using app context ass suggested by CommonsWare Log.i("DBHELPER1", "cxt"+mCxt+" / instance: "+mInstance); if (mInstance == null) { mInstance = new DatabaseHelper(cxt.getApplicationContext()); } Log.i("DBHELPER2", "cxt"+mCxt+" / instance: "+mInstance); mCxt = cxt; return mInstance; } //private constructor private DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); this.mCxt = context; } @Override public void onCreate(SQLiteDatabase db) { //some tables created here } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { //upgrade code here } It really works great in most cases. But from time to time I get a log similar to this: 06-10 23:49:59.621: I/DBHELPER1(26499): cxtcom.bananout.Bananout@407152c8 / instance: com.bananout.helpers.DatabaseHelper@40827560 06-10 23:49:59.631: I/DBHELPER2(26499): cxtcom.bananout.Bananout@407152c8 / instance: com.bananout.helpers.DatabaseHelper@40827560 06-10 23:49:59.631: I/DetailsLoader(26499): Get event details offline / db helper: com.bananout.helpers.DatabaseHelper@40827560 06-10 23:49:59.631: I/DBHELPER1(26499): cxtcom.bananout.Bananout@407152c8 / instance: com.bananout.helpers.DatabaseHelper@40827560 06-10 23:49:59.651: I/DBHELPER2(26499): cxtcom.bananout.Bananout@407152c8 / instance: com.bananout.helpers.DatabaseHelper@40827560 This line Log.i(TAG, "Get details offline / db: "+db); never gets called! No Exceptions, silence. Plus, the thread with the Loader is not running anymore. So nothing past this line SQLiteDatabase db=DatabaseHelper.getInstance(this.getContext()).getWritableDatabase(); gets executed. What can possibly go wrong on this line?

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• EJB / JSF java.lang.ClassNotFoundException: com.ericsantanna.jobFC.dao.DAOFactoryRemote from [Module "com.sun.jsf-impl:main" from local module loader

  - by Eric Sant'Anna

  I'm in my first time using EJB and JSF, and I can't resolve this: 20:23:12,457 Grave [javax.enterprise.resource.webcontainer.jsf.application] (http-localhost-127.0.0.1-8081-2) com.ericsantanna.jobFC.dao.DAOFactoryRemote from [Module "com.sun.jsf-impl:main" from local module loader @439db2b2 (roots: C:\jboss-as-7.1.1.Final\modules)]: java.lang.ClassNotFoundException: com.ericsantanna.jobFC.dao.DAOFactoryRemote from [Module "com.sun.jsf-impl:main" from local module loader @439db2b2 (roots: C:\jboss-as-7.1.1.Final\modules)] I'm getting this when I do an action like a selectOneMenu or a commandButton click. DAOFactory.class @Singleton @Remote(DAOFactoryRemote.class) public class DAOFactory implements DAOFactoryRemote { private static final long serialVersionUID = 6030538139815885895L; @PersistenceContext private EntityManager entityManager; @EJB private JobDAORemote jobDAORemote; /** * Default constructor. */ public DAOFactory() { // TODO Auto-generated constructor stub } @Override public JobDAORemote getJobDAO() { JobDAO jobDAO = (JobDAO) jobDAORemote; jobDAO.setEntityManager(entityManager); return jobDAO; } JobDAO.class @Stateless @Remote(JobDAORemote.class) public class JobDAO implements JobDAORemote { private static final long serialVersionUID = -5483992924812255349L; private EntityManager entityManager; /** * Default constructor. */ public JobDAO() { // TODO Auto-generated constructor stub } @Override public void insert(Job t) { entityManager.persist(t); } @Override public Job findById(Class<Job> classe, Long id) { return entityManager.getReference(classe, id); } @Override public Job findByName(Class<Job> clazz, String name) { return entityManager .createQuery("SELECT job FROM " + clazz.getName() + " job WHERE job.nome = :nome" , Job.class) .setParameter("name", name) .getSingleResult(); } ... TriggerFormBean.class @ManagedBean @ViewScoped @Stateless public class TriggerFormBean implements Serializable { private static final long serialVersionUID = -3293560384606586480L; @EJB private DAOFactoryRemote daoFactory; @EJB private TriggerManagerRemote triggerManagerRemote; ... triggerForm.xhtml (a portion with problem) </p:layoutUnit> <p:layoutUnit id="eastConditionPanel" position="center" size="50%"> <p:panel header="Conditions to Release" style="width:97%;height:97%;"> <h:panelGrid columns="2" cellpadding="3"> <h:outputLabel value="Condition Name:" for="conditionName" /> <p:inputText id="conditionName" value="#{triggerFormBean.newCondition.name}" /> </h:panelGrid> <p:commandButton value="Add Condition" update="conditionsToReleaseList" id="addConditionToRelease" actionListener="#{triggerFormBean.addNewCondition}" /> <p:orderList id="conditionsToReleaseList" value="#{triggerFormBean.trigger.conditionsToRelease}" var="condition" controlsLocation="none" itemLabel="#{condition.name}" itemValue="#{condition}" iconOnly="true" style="width:97%;heigth:97%;"/> </p:panel> </p:layoutUnit> In TriggerFormBean.class if comments daoFactory we get the same exception with triggerManagerRemote, both annotated with @EJB. I'm don't understand the relationship between my DAOFactory and the "Module com.sun.jsf-impl:main"... Thanks.

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• Exceptions confusion

  - by Misiur

  Hi there. I'm trying to build site using OOP in PHP. Everyone is talking about Singleton, hermetization, MVC, and using exceptions. So I've tried to do it like this: Class building whole site: class Core { public $is_core; public $theme; private $db; public $language; private $info; static private $instance; public function __construct($lang = 'eng', $theme = 'default') { if(!self::$instance) { try { $this->db = new sdb(DB_TYPE.':host='.DB_HOST.';dbname='.DB_NAME, DB_USER, DB_PASS); } catch(PDOException $e) { throw new CoreException($e->getMessage()); } try { $this->language = new Language($lang); } catch(LangException $e) { throw new CoreException($e->getMessage()); } try { $this->theme = new Theme($theme); } catch(ThemeException $e) { throw new CoreException($e->getMessage()); } } return self::$instance; } public function getSite($what) { return $this->language->getLang(); } private function __clone() { } } Class managing themes class Theme { private $theme; public function __construct($name = 'default') { if(!is_dir("themes/$name")) { throw new ThemeException("Unable to load theme $name"); } else { $this->theme = $name; } } public function getTheme() { return $this->theme; } public function display($part) { if(!is_file("themes/$this->theme/$part.php")) { throw new ThemeException("Unable to load theme part: themes/$this->theme/$part.php"); } else { return 'So far so good'; } } } And usage: error_reporting(E_ALL); require_once('config.php'); require_once('functions.php'); try { $core = new Core(); } catch(CoreException $e) { echo 'Core Exception: '.$e->getMessage(); } echo $core->theme->getTheme(); echo "<br />"; echo $core->language->getLang(); try { $core->theme->display('footer'); } catch(ThemeException $e) { echo $e->getMessage(); } I don't like those exception handlers - i don't want to catch them like some pokemons... I want to use things simple: $core-theme-display('footer'); And if something is wrong, and debug mode is enabled, then aplication show error. What should i do?

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• Calling a JAVA method from C++ with JNI, no parameters

  - by PRNDL Development Studios

  Please bear with me, I am an iPhone developer and this whole android this confuses me a bit. I have some c++ methods that are called from a cocos2d-x CCMenuItem. Therefore I cannot send any parameters, according to the docs. I need to open a url with the android browser which will require me to call a JAVA function to start a new intent. I understand that I need to create a VM, however the below code gives me the error: jni/../../Classes/MyClass.cpp:184: error: 'JNI_CreateJavaVM' was not declared in this scope I was looking at this thread: Calling a java method from c++ in Android But he uses parameters, and I can't do that. And I don't see where those are in his code to just make them myself. I don't know what the string should be in the 'Find Class' method. Also, I assume it is pretty terrible to create a new VM instance in every method I need to call. How would I create one as a singleton to use across the board? This is my c++ code called by my menu item: #include <jni.h> ... JavaVM *vm; // Global ... void OptionsScene::website(){ JNIEnv *env; JavaVMInitArgs vm_args; vm_args.version = JNI_VERSION_1_2; vm_args.nOptions = 0; vm_args.ignoreUnrecognized = 1; jint result = JNI_CreateJavaVM(&vm, (void **)&env, &vm_args); // This line still errors jclass clazz = env->FindClass("com/prndl/project/WebExecute"); jmethodID method = env->GetMethodID(clazz, "website", "(Ljava/lang/String;)V"); env->CallVoidMethod(NULL,method); vm->DestroyJavaVM(); And this is the JAVA Method that I need to call: public class WebExecute extends Activity{ public void website(){ Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.google.com")); startActivity(browserIntent); } } Honestly, I am struggling with this, any help is appreciated. Thanks.

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• C#, cannot understand this error?

  - by 5YrsLaterDBA

  I am using VS2008. I have a project, SystemSoftware project, connect with a database and we are using L2E. I have a RuntimeInfo class which contains some shared information there. It looks like this: public class RuntimeInfo { public const int PWD_ExpireDays = 30; private static RuntimeInfo thisObj = new RuntimeInfo(); public static string AndeDBConnStr = ConfigurationManager.ConnectionStrings["AndeDBEntities"].ConnectionString; private RuntimeInfo() { } /// <summary> /// /// </summary> /// <returns>Return this singleton object</returns> public static RuntimeInfo getRuntimeInfo() { return thisObj; } } Now I added a helper project, AndeDataViewer, to the solution which creates a simple UI to display data from the database for testing/verification purpose. I don't want to create another set of Entity Data Model in the helper project. I just added all related files as a link in the new helper project. In the AndeDataViewer project, I get the connection string from above RuntimeInfo class which is a class from my SystemSoftware project as a linked file. The code in AndeDataViewer is like this: public class DbAccess : IDisposable { private String connStr = String.Empty; public DbAccess() { connStr = RuntimeInfo.AndeDBConnStr; } } My SystemSoftware works fine that means the RuntimeInfo class has no problem there. But when I run my AndeDataViewer, the statement inside above constructor, connStr = RuntimeInfo.AndeDBConnStr; , throws an exception. The exception is copied here: System.TypeInitializationException was unhandled Message="The type initializer for 'MyCompany.SystemSoftware.SystemInfo.RuntimeInfo' threw an exception." Source="AndeDataViewer" TypeName="MyCompany.SystemSoftware.SystemInfo.RuntimeInfo" StackTrace: at AndeDataViewer.DbAccess..ctor() in C:\workspace\SystemSoftware\Other\AndeDataViewer\AndeDataViewer\DbAccess.cs:line 17 at AndeDataViewer.Window1.rbRawData_Checked(Object sender, RoutedEventArgs e) in C:\workspace\SystemSoftware\Other\AndeDataViewer\AndeDataViewer\Window1.xaml.cs:line 69 at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) .... InnerException: System.NullReferenceException Message="Object reference not set to an instance of an object." Source="AndeDataViewer" StackTrace: at MyCompany.SystemSoftware.SystemInfo.RuntimeInfo..cctor() in C:\workspace\SystemSoftware\SystemSoftware\src\systeminfo\RuntimeInfo.cs:line 24 InnerException: I cannot understand this because it looks fine to me but why there is an exception? we cannot access static variable when a class is a linked class? A linked class should be the same as the local class I think. "Linked" here means when I add file I use "Add As Link".

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• Communicate progress from local Service

  - by kpdvx

  An application I'm building uses a local Service for downloading files from the web to the phone's SD card. In this app users can browse lists of books, and read them while online. A user can also download a pdf copy of a book for offline viewing. To handle downloads I'm using a locally bound Service. I do not want this Service to run all the time, only when downloading files. So that the Service can shut itself down when its tasks are complete, I am not binding to the service, rather I'm sending an "enqueue for download" command through the Intent passed to Context.startService. Books available for download are shown in a list. A user can choose to download a book by clicking on its row in the list. On download, I need to show download progress using a ProgressBar on the actual book list row. I need to also show, on the rows, if a book is enqueued for download, or if its download has completed or failed. The books can be shown in different activities throughout the application--in search, or in the user's list of favorite books, for example. When the books are shown in different places, these are not the same objects, but they are uniquely identified by their bookId. Because I do not want to bind to the service from every Activity, my tentative plan was to use a public static final HashMap on the Service class itself to contain a mapping of bookId to download status, an enum of enqueued, downloading, cancelled, etc. Each book view, when displayed, would check this static HashMap, and if the bookId is in the map, retrieve and display its status. I don't particularly like this idea, but at the moment it's the only way I can think of to retrieve status from the Service without having to bind to it and start it. Additionally I need to retrieve download progress percent from the Service, for a given bookId, if it is the active download. Again I'd rather not bind to the service from every activity, so I'm not sure how to go about retrieving current progress from the Service. My current plan is to use some sort of singleton mediator, that the Service will push updates to, and the views can read from. But I'm not terribly happy with this idea. The reason I'd like to avoid binding to the Service from each Activity is 1.) I'm already running another Service and 2.) binding is verbose and I'd like to avoid needing to pass around a reference to the Service (but admittedly this isn't too much of a problem). Perhaps binding to the local Service isn't expensive enough to warrant this other setup? Should I not be concerned about binding to it from each Activity? Maybe this is a non-issue?

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• Dependency Injection in ASP.NET MVC NerdDinner App using Ninject

  - by shiju

  In this post, I am applying Dependency Injection to the NerdDinner application using Ninject. The controllers of NerdDinner application have Dependency Injection enabled constructors. So we can apply Dependency Injection through constructor without change any existing code. A Dependency Injection framework injects the dependencies into a class when the dependencies are needed. Dependency Injection enables looser coupling between classes and their dependencies and provides better testability of an application and it removes the need for clients to know about their dependencies and how to create them. If you are not familiar with Dependency Injection and Inversion of Control (IoC), read Martin Fowler’s article Inversion of Control Containers and the Dependency Injection pattern. The Open Source Project NerDinner is a great resource for learning ASP.NET MVC.  A free eBook provides an end-to-end walkthrough of building NerdDinner.com application. The free eBook and the Open Source Nerddinner application are extremely useful if anyone is trying to lean ASP.NET MVC. The first release of  Nerddinner was as a sample for the first chapter of Professional ASP.NET MVC 1.0. Currently the application is updating to ASP.NET MVC 2 and you can get the latest source from the source code tab of Nerddinner at http://nerddinner.codeplex.com/SourceControl/list/changesets. I have taken the latest ASP.NET MVC 2 source code of the application and applied  Dependency Injection using Ninject and Ninject extension Ninject.Web.Mvc.Ninject &  Ninject.Web.MvcNinject is available at http://github.com/enkari/ninject and Ninject.Web.Mvc is available at http://github.com/enkari/ninject.web.mvcNinject is a lightweight and a great dependency injection framework for .NET.  Ninject is a great choice of dependency injection framework when building ASP.NET MVC applications. Ninject.Web.Mvc is an extension for ninject which providing integration with ASP.NET MVC.Controller constructors and dependencies of NerdDinner application Listing 1 – Constructor of DinnersController  public DinnersController(IDinnerRepository repository) {     dinnerRepository = repository; }  Listing 2 – Constrcutor of AccountControllerpublic AccountController(IFormsAuthentication formsAuth, IMembershipService service) {     FormsAuth = formsAuth ?? new FormsAuthenticationService();     MembershipService = service ?? new AccountMembershipService(); }  Listing 3 – Constructor of AccountMembership – Concrete class of IMembershipService public AccountMembershipService(MembershipProvider provider) {     _provider = provider ?? Membership.Provider; }    Dependencies of NerdDinnerDinnersController, RSVPController SearchController and ServicesController have a dependency with IDinnerRepositiry. The concrete implementation of IDinnerRepositiry is DinnerRepositiry. AccountController has dependencies with IFormsAuthentication and IMembershipService. The concrete implementation of IFormsAuthentication is FormsAuthenticationService and the concrete implementation of IMembershipService is AccountMembershipService. The AccountMembershipService has a dependency with ASP.NET Membership Provider. Dependency Injection in NerdDinner using NinjectThe below steps will configure Ninject to apply controller injection in NerdDinner application.Step 1 – Add reference for NinjectOpen the  NerdDinner application and add  reference to Ninject.dll and Ninject.Web.Mvc.dll. Both are available from http://github.com/enkari/ninject and http://github.com/enkari/ninject.web.mvcStep 2 – Extend HttpApplication with NinjectHttpApplication Ninject.Web.Mvc extension allows integration between the Ninject and ASP.NET MVC. For this, you have to extend your HttpApplication with NinjectHttpApplication. Open the Global.asax.cs and inherit your MVC application from  NinjectHttpApplication instead of HttpApplication.   public class MvcApplication : NinjectHttpApplication Then the Application_Start method should be replace with OnApplicationStarted method. Inside the OnApplicationStarted method, call the RegisterAllControllersIn() method.   protected override void OnApplicationStarted() {     AreaRegistration.RegisterAllAreas();     RegisterRoutes(RouteTable.Routes);     ViewEngines.Engines.Clear();     ViewEngines.Engines.Add(new MobileCapableWebFormViewEngine());     RegisterAllControllersIn(Assembly.GetExecutingAssembly()); }  The RegisterAllControllersIn method will enables to activating all controllers through Ninject in the assembly you have supplied .We are passing the current assembly as parameter for RegisterAllControllersIn() method. Now we can expose dependencies of controller constructors and properties to request injectionsStep 3 – Create Ninject ModulesWe can configure your dependency injection mapping information using Ninject Modules.Modules just need to implement the INinjectModule interface, but most should extend the NinjectModule class for simplicity. internal class ServiceModule : NinjectModule {     public override void Load()     {                    Bind<IFormsAuthentication>().To<FormsAuthenticationService>();         Bind<IMembershipService>().To<AccountMembershipService>();                  Bind<MembershipProvider>().ToConstant(Membership.Provider);         Bind<IDinnerRepository>().To<DinnerRepository>();     } } The above Binding inforamtion specified in the Load method tells the Ninject container that, to inject instance of DinnerRepositiry when there is a request for IDinnerRepositiry and  inject instance of FormsAuthenticationService when there is a request for IFormsAuthentication and inject instance of AccountMembershipService when there is a request for IMembershipService. The AccountMembershipService class has a dependency with ASP.NET Membership provider. So we configure that inject the instance of Membership Provider. When configuring the binding information, you can specify the object scope in you application.There are four built-in scopes available in Ninject:Transient  -  A new instance of the type will be created each time one is requested. (This is the default scope). Binding method is .InTransientScope()   Singleton - Only a single instance of the type will be created, and the same instance will be returned for each subsequent request. Binding method is .InSingletonScope()Thread -  One instance of the type will be created per thread. Binding method is .InThreadScope() Request -  One instance of the type will be created per web request, and will be destroyed when the request ends. Binding method is .InRequestScope() Step 4 – Configure the Ninject KernelOnce you create NinjectModule, you load them into a container called the kernel. To request an instance of a type from Ninject, you call the Get() extension method. We can configure the kernel, through the CreateKernel method in the Global.asax.cs. protected override IKernel CreateKernel() {     var modules = new INinjectModule[]     {         new ServiceModule()     };       return new StandardKernel(modules); } Here we are loading the Ninject Module (ServiceModule class created in the step 3)  onto the container called the kernel for performing dependency injection.Source CodeYou can download the source code from http://nerddinneraddons.codeplex.com. I just put the modified source code onto CodePlex repository. The repository will update with more add-ons for the NerdDinner application.

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• HttpContext.Items and Server.Transfer/Execute

  - by Rick Strahl

  A few days ago my buddy Ben Jones pointed out that he ran into a bug in the ScriptContainer control in the West Wind Web and Ajax Toolkit. The problem was basically that when a Server.Transfer call was applied the script container (and also various ClientScriptProxy script embedding routines) would potentially fail to load up the specified scripts. It turns out the problem is due to the fact that the various components in the toolkit use request specific singletons via a Current property. I use a static Current property tied to a Context.Items[] entry to handle this type of operation which looks something like this: /// <summary> /// Current instance of this class which should always be used to /// access this object. There are no public constructors to /// ensure the reference is used as a Singleton to further /// ensure that all scripts are written to the same clientscript /// manager. /// </summary> public static ClientScriptProxy Current { get { if (HttpContext.Current == null) return new ClientScriptProxy(); ClientScriptProxy proxy = null; if (HttpContext.Current.Items.Contains(STR_CONTEXTID)) proxy = HttpContext.Current.Items[STR_CONTEXTID] as ClientScriptProxy; else { proxy = new ClientScriptProxy(); HttpContext.Current.Items[STR_CONTEXTID] = proxy; } return proxy; } } The proxy is attached to a Context.Items[] item which makes the instance Request specific. This works perfectly fine in most situations EXCEPT when you’re dealing with Server.Transfer/Execute requests. Server.Transfer doesn’t cause Context.Items to be cleared so both the current transferred request and the original request’s Context.Items collection apply. For the ClientScriptProxy this causes a problem because script references are tracked on a per request basis in Context.Items to check for script duplication. Once a script is rendered an ID is written into the Context collection and so considered ‘rendered’: // No dupes - ref script include only once if (HttpContext.Current.Items.Contains( STR_SCRIPTITEM_IDENTITIFIER + fileId ) ) return; HttpContext.Current.Items.Add(STR_SCRIPTITEM_IDENTITIFIER + fileId, string.Empty); where the fileId is the script name or unique identifier. The problem is on the Transferred page the item will already exist in Context and so fail to render because it thinks the script has already rendered based on the Context item. Bummer. The workaround for this is simple once you know what’s going on, but in this case it was a bitch to track down because the context items are used in many places throughout this class. The trick is to determine when a request is transferred and then removing the specific keys. The first issue is to determine if a script is in a Trransfer or Execute call: if (HttpContext.Current.CurrentHandler != HttpContext.Current.Handler) Context.Handler is the original handler and CurrentHandler is the actual currently executing handler that is running when a Transfer/Execute is active. You can also use Context.PreviousHandler to get the last handler and chain through the whole list of handlers applied if Transfer calls are nested (dog help us all for the person debugging that). For the ClientScriptProxy the full logic to check for a transfer and remove the code looks like this: /// <summary> /// Clears all the request specific context items which are script references /// and the script placement index. /// </summary> public void ClearContextItemsOnTransfer() { if (HttpContext.Current != null) { // Check for Server.Transfer/Execute calls - we need to clear out Context.Items if (HttpContext.Current.CurrentHandler != HttpContext.Current.Handler) { List<string> Keys = HttpContext.Current.Items.Keys.Cast<string>().Where(s => s.StartsWith(STR_SCRIPTITEM_IDENTITIFIER) || s == STR_ScriptResourceIndex).ToList(); foreach (string key in Keys) { HttpContext.Current.Items.Remove(key); } } } } along with a small update to the Current property getter that sets a global flag to indicate whether the request was transferred: if (!proxy.IsTransferred && HttpContext.Current.Handler != HttpContext.Current.CurrentHandler) { proxy.ClearContextItemsOnTransfer(); proxy.IsTransferred = true; } return proxy; I know this is pretty ugly, but it works and it’s actually minimal fuss without affecting the behavior of the rest of the class. Ben had a different solution that involved explicitly clearing out the Context items and replacing the collection with a manually maintained list of items which also works, but required changes through the code to make this work. In hindsight, it would have been better to use a single object that encapsulates all the ‘persisted’ values and store that object in Context instead of all these individual small morsels. Hindsight is always 20/20 though :-}. If possible use Page.Items ClientScriptProxy is a generic component that can be used from anywhere in ASP.NET, so there are various methods that are not Page specific on this component which is why I used Context.Items, rather than the Page.Items collection.Page.Items would be a better choice since it will sidestep the above Server.Transfer nightmares as the Page is reloaded completely and so any new Page gets a new Items collection. No fuss there. So for the ScriptContainer control, which has to live on the page the behavior is a little different. It is attached to Page.Items (since it’s a control): /// <summary> /// Returns a current instance of this control if an instance /// is already loaded on the page. Otherwise a new instance is /// created, added to the Form and returned. /// /// It's important this function is not called too early in the /// page cycle - it should not be called before Page.OnInit(). /// /// This property is the preferred way to get a reference to a /// ScriptContainer control that is either already on a page /// or needs to be created. Controls in particular should always /// use this property. /// </summary> public static ScriptContainer Current { get { // We need a context for this to work! if (HttpContext.Current == null) return null; Page page = HttpContext.Current.CurrentHandler as Page; if (page == null) throw new InvalidOperationException(Resources.ERROR_ScriptContainer_OnlyWorks_With_PageBasedHandlers); ScriptContainer ctl = null; // Retrieve the current instance ctl = page.Items[STR_CONTEXTID] as ScriptContainer; if (ctl != null) return ctl; ctl = new ScriptContainer(); page.Form.Controls.Add(ctl); return ctl; } } The biggest issue with this approach is that you have to explicitly retrieve the page in the static Current property. Notice again the use of CurrentHandler (rather than Handler which was my original implementation) to ensure you get the latest page including the one that Server.Transfer fired. Server.Transfer and Server.Execute are Evil All that said – this fix is probably for the 2 people who are crazy enough to rely on Server.Transfer/Execute. :-} There are so many weird behavior problems with these commands that I avoid them at all costs. I don’t think I have a single application that uses either of these commands… Related Resources Full source of ClientScriptProxy.cs (repository) Part of the West Wind Web Toolkit Static Singletons for ASP.NET Controls Post © Rick Strahl, West Wind Technologies, 2005-2010Posted in ASP.NET  

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• CodePlex Daily Summary for Friday, September 07, 2012

  CodePlex Daily Summary for Friday, September 07, 2012Popular ReleasesUmbraco CMS: Umbraco 4.9.0: Whats newThe media section has been overhauled to support HTML5 uploads, just drag and drop files in, even multiple files are supported on any HTML5 capable browser. The folder content overview is also much improved allowing you to filter it and perform common actions on your media items. The Rich Text Editor’s “Media” button now uses an embedder based on the open oEmbed standard (if you’re upgrading, enable the media button in the Rich Text Editor datatype settings and set TidyEditorConten...menu4web: menu4web 0.4.1 - javascript menu for web sites: This release is for those who believe that global variables are evil. menu4web has been wrapped into m4w singleton object. Added "Vertical Tabs" example which illustrates object notation.WinRT XAML Toolkit: WinRT XAML Toolkit - 1.2.1: WinRT XAML Toolkit based on the Windows 8 RTM SDK. Download the latest source from the SOURCE CODE page. For compiled version use NuGet. You can add it to your project in Visual Studio by going to View/Other Windows/Package Manager Console and entering: PM> Install-Package winrtxamltoolkit Features AsyncUI extensions Controls and control extensions Converters Debugging helpers Imaging IO helpers VisualTree helpers Samples Recent changes NOTE: Namespace changes DebugConsol...iPDC - Free Phasor Data Concentrator: iPDC-v1.3.1: iPDC suite version-1.3.1, Modifications and Bug Fixed (from v 1.3.0) New User Manual for iPDC-v1.3.1 available on websites. Bug resolved : PMU Simulator TCP connection error and hang connection for client (PDC). Now PMU Simulator (server) can communicate more than one PDCs (clients) over TCP and UDP parallely. PMU Simulator is now sending the exact data frames as mentioned in data rate by user. PMU Simulator data rate has been verified by iPDC database entries and PMU Connection Tes...Microsoft SQL Server Product Samples: Database: AdventureWorks OData Feed: The AdventureWorks OData service exposes resources based on specific SQL views. The SQL views are a limited subset of the AdventureWorks database that results in several consuming scenarios: CompanySales Documents ManufacturingInstructions ProductCatalog TerritorySalesDrilldown WorkOrderRouting How to install the sample You can consume the AdventureWorks OData feed from http://services.odata.org/AdventureWorksV3/AdventureWorks.svc. You can also consume the AdventureWorks OData fe...Desktop Google Reader: 1.4.6: Sorting feeds alphabetical is now optional (see preferences window)DotNetNuke® Community Edition CMS: 06.02.03: Major Highlights Fixed issue where mailto: links were not working when sending bulk email Fixed issue where uses did not see friendship relationships Problem is in 6.2, which does not show in the Versions Affected list above. Fixed the issue with cascade deletes in comments in CoreMessaging_Notification Fixed UI issue when using a date fields as a required profile property during user registration Fixed error when running the product in debug mode Fixed visibility issue when...Microsoft Ajax Minifier: Microsoft Ajax Minifier 4.65: Fixed null-reference error in the build task constructor.B INI Sharp Library: B INI Sharp Library v1.0.0.0 Final Realsed: The frist realsedActive Social Migrator: ActiveSocialMigrator 1.0.0 Beta: Beta release for the Active Social Migration tool.EntLib.com????????: ??????demo??-For SQL 2005-2008: EntLibShopping ???v3.0 - ??????demo??，?????SQL SERVER 2005/2008/2008 R2/2012 ??????。 ??（??）??????。 THANKS.Sistem LPK Pemkot Semarang: Panduan Penggunaan Sistem LPK: Panduan cara menggunakan Aplikasi Sistem LPK Bagian Pembangunan Kota SemarangActive Forums for DotNetNuke CMS: Active Forums 5.0.0 RC: RC release of Active Forums 5.0.Droid Explorer: Droid Explorer 0.8.8.7 Beta: Bug in the display icon for apk's, will fix with next release Added fallback icon if unable to get the image/icon from the Cloud Service Removed some stale plugins that were either out dated or incomplete. Added handler for *.ab files for restoring backups Added plugin to create device backups Backups stored in %USERPROFILE%\Android Backups\%DEVICE_ID%\ Added custom folder icon for the android backups directory better error handling for installing an apk bug fixes for the Runn...The Visual Guide for Building Team Foundation Server 2012 Environments: Version 1: --Nearforums - ASP.NET MVC forum engine: Nearforums v8.5: Version 8.5 of Nearforums, the ASP.NET MVC Forum Engine. New features include: Built-in search engine using Lucene.NET Flood control improvements Notifications improvements: sync option and mail body View Roadmap for more details webdeploy package sha1 checksum: 961aff884a9187b6e8a86d68913cdd31f8deaf83WiX Toolset: WiX Toolset v3.6: WiX Toolset v3.6 introduces the Burn bootstrapper/chaining engine and support for Visual Studio 2012 and .NET Framework 4.5. Other minor functionality includes: WixDependencyExtension supports dependency checking among MSI packages. WixFirewallExtension supports more features of Windows Firewall. WixTagExtension supports Software Id Tagging. WixUtilExtension now supports recursive directory deletion. Melt simplifies pure-WiX patching by extracting .msi package content and updating .w...Iveely Search Engine: Iveely Search Engine （0.2.0）: ????ISE?0.1.0??，?????，ISE?0.2.0?????????，???????，????????20???follow?ISE，????，??ISE??????????，??????????，?????????，?????????0.2.0??????，??????????。 Iveely Search Engine ?0.2.0?????????“??????????”，??????，?????????，???????，???????????????????，????、????????????。???0.1.0????????????： 1. ??“????” ??。??????????，?????????，???????????????????。??：????????，????????????，??????????????????。??????。 2. ??“????”??。?0.1.0??????，???????，???????????????，?????????????，????????，?0.2.0?，???????...GmailDefaultMaker: GmailDefaultMaker 3.0.0.2: Add QQ Mail BugfixSmart Data Access layer: Smart Data access Layer Ver 3: In this version support executing inline query is added. Check Documentation section for detail.New ProjectsAdding 2013 Jewish Holidays for Outlook2003: Instruction: Copy the outlook.hol file to your compuer where Outlook2003 is installed. Double click the file, choose "Israel" and continue. That's it Agilcont System: Sistema de contabilidad para empresas privadas de preferencia para cajas que trabajan con efectivo en soles, dolares y con el material oroARB (A Request Broker): The idea is something like a Request Broker, but with some additional functionality.BATTLE.NET - SDK: This SDK provides the ability to use the Battle.net (Blizzard) Services for all supported Games such Diablo 3, World of Warcraft. Container Terminal System: SummaryDeclarative UX Streaming Data Language for the Cloud: Bringing a better communication paradigm for media and data..Get User Profile Information from SharePoint UserProfile Service: Used SharePoint object model to get the user profile information from the User Profile Service.Guess The City & State Windows 8 Source Code: Source code for Guess The City & State in Malaysia Windows 8 AppJquery Tree: This project is to demonstrate tree basic functionality.MCEBuddy 2.x: Convert and Remove Commercials for your Windows Media CenterMvcDesign: MvcDesign engine implementation projectMy Task Manager: This is a task manager module for DotNetNuke. I am using it to get started developing modules.MyAppwithbranches: MyAppwithbranchesProjecte prova: rpyGEO: pyGEO is a python package capable of parsing microarray data files. It also has a primitive plotting function.Scarlet Road: Scarlet Road is a top-down shooter. It's you against an unending horde of monsters.simplecounter: A simple counter, cick and counter.SiteEmpires: ????????Soundcloud Loader: Simple Tool for downloading Tracks from Soundcloud.Windows Phone Samples: Windows Phone code samples.

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• CodePlex Daily Summary for Tuesday, March 23, 2010

  CodePlex Daily Summary for Tuesday, March 23, 2010New Projects.NET StarCraft II Replay Parser: A .NET 3.5 Library used to parse StarCraft II replays. Developed in C# 3.5.BackToBasics "B2B" Chat: With technology and software getting more and more complicated, why not get back to basics with BackToBasicsChat. B2B allows you to chat over a ser...Dark Neuron Game Engine: Dark Neuron allows you to easily create fun and interesting games with no need of developing basic game components. This engine is developed for C#...DeepZoom Pivot Constructor: Library to make building DeepZoom images and Pivot displays simpler.ePaper reader: The project is aimed at creating a tool which helps in reading electronic editions of news papers(pdf/flash)FSharpPageProvider for EPiServer CMS 6: This project starts as the port of EPiServer XmlPageProvider to F# programming language. Hammock for REST: Hammock is a REST library for .NET that greatly simplifies consuming and wrapping RESTful services.Kirill Osenkov: Various small projects, tools, utilities and samples by Kirill OsenkovliveDB: liveDB - web client for sql serverLucilla Framework: lucilla frameworkMVC Foolproof Validation: MVC Foolproof Validation aims to extend the Data Annotation validation provided in ASP.NET MVC. Initial efforts are focused on adding contingent va...MVC2Forums: MVC2Forums is simply a forum system based upon MVC2.Mvvm Foundation Silverlight: Mvvm Foundation Silverlight is a library of classes that are helpful when building Silverlight applications based in the MVVM pattern. This librar...MyPersonalWebsite: This is my personal web site developed using ASP.NET MVC 2Planner: Planner makes it easier for all peoples to plan your tasks. It's developed in Delphi.Prose: Prose is an playground for an experimental JavaScript like language compiler. Eventually it will implement 0-CFA, CFA2, and a Tracing JITQuestTracker: QuestTracker is a todo list presented in the format of a quest tracking list such as the one in World of Warcraft.SevenZipLib: SevenZipLib is a C# interface to the 7-zip library.SimpleGeo .Net: .Net Client library for the SimpleGeo.com serviceNew ReleasesAutenticar no OpenLDAP utilizando pGIna: DLL LDAPAuth Plus: New Group: No LoginBMap.NET: BMap.NET 2: This is the 2nd version of BMap.NET. It has included these tags: Bing Maps, and "About BMap.NET".Cronos: Version 2.04: This is primarily a bug-fix release. Several numerical issues have been resolved, and a resource leak (of MS Windows graphics objects) has been fi...EV Dashboard: v1.0: This release includes support for an App.config file and Auto Connect, which will connect to the specified BMS at startup. Note: You still have to ...GKO Libraries: GKO Libraries 0.1 Beta: 0.1 Beta Added More utilities and functions RefactoringsGLB Virtual Player Builder: 0.4.2 Beta: Beta build that includes a new player creator.HKGolden Express: HKGoldenExpress (Build 201003222215): New features: (None) Bug fix: Fixed bugs of unable to parse XML file stream returned from HKGolden API, as the encoding of XML file stream chang...jQuery Web Controls ASP.Net: jQueryWebControls 1.1.1.2: En esta versión se han corregido problemas existentes en la ejecución de los scripts de jquery cuando se utilizaban MasterPage y/o Ajax Control Too...LightKit: Version 0.2.2: Fixed: fixed bug when CollectionItemsEditor ditermines IsChanged property incorrectly fixed ObjectEditor`a thisstring propertyName method wrong l...LINQ to Twitter: LINQ to Twitter Beta v2.0.8: New items added since v1.1 include: Support for OAuth (via DotNetOpenAuth), secure communication via https, VB language support, serialization of ...MapWindow6: MapWindow 6.0 msi (March 22): This version fixes the icons for the desktop installer and changes the install directory to Program Files\MapWindow instead of Program Files\ISU.Math.NET Numerics: 2010.3.22.1334 Build: Latest alpha buildMiniCalendar Web Part: MiniCalendar Web Part 1.8: A small web part to display links to events stored in a list (or document library) in a mini calendar (in month view mode). It shows tooltips for t...OCInject: Release Two: This release brings some missing features such as Singleton support, Func<T> factories and child containers. It, also, has an updated constructor ...Phalanger - The PHP Language Compiler for the .NET Framework: 2.0 (March 2010): Installer of the latest binaries of Phalanger 2.0 (March 2010) and its integration into Visual Studio 2008. Easy installer with automatic IIS int...Planner: Planner: firstQuestTracker: QuestTracker 0.1: This is the preliminary release of QuestTracker. There's not much documentation or many features yet, but it is functional. Any feedback would be a...QuestTracker: QuestTracker 0.1.1: Bugfix for QuestTracker 0.1QuestTracker: QuestTracker 0.1.2: Fixes an issue with saving the quest list.Rawr: Rawr 2.3.13: We're pleased to announce that, after long last, Rawr3 has entered public beta. You're still welcome to continue using Rawr2 (that's what you're re...Single Web Session: Alpha Model Plugin: !How to use Single Web Session add following line into your web config <httpModules> <add name="SingleSession" type="SingleWebSession.Model.W...SMIL - SharePoint Map Integration Layer: SMIL 1.0: Custom data field Extracts Lat/Lon from EXIF from images being uploaded. Map Web Part Filter with SharePoint views Filter by connecting to...sTASKedit: sTASKedit 42532 (Developer Alpha): This release is only to verify the currently decoded task structure... Supported files: tasks.data (v1.3.6 client)VCC: Latest build, v2.1.30322.0: Automatic drop of latest buildVisual Studio DSite: Advanced Notepad (Visual C++ 2008): An notepad written in c that can save in a rich text file format.Wallpaper Rotator: Wallpaper Rotator 0.5: Wallpaper Rotator 0.5 This version includes the following improvements: Saving the choice of "Random Order (Shuffle Mode)" Updating the configu...Most Popular ProjectsMetaSharpRawrWBFS ManagerSilverlight ToolkitASP.NET Ajax LibraryMicrosoft SQL Server Product Samples: DatabaseAJAX Control ToolkitLiveUpload to FacebookWindows Presentation Foundation (WPF)ASP.NETMost Active ProjectsRawrjQuery Library for SharePoint Web ServicesBlogEngine.NETLINQ to TwitterPHPExcelFarseer Physics EngineFacebook Developer ToolkitNB_Store - Free DotNetNuke Ecommerce Catalog Modulepatterns & practices: Composite WPF and SilverlightN2 CMS

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• Retrieving a list of eBay categories using the .NET SDK and GetCategoriesCall

  - by Bill Osuch

  eBay offers a .Net SDK for its Trading API - this post will show you the basics of making an API call and retrieving a list of current categories. You'll need the category ID(s) for any apps that post or search eBay. To start, download the latest SDK from https://www.x.com/developers/ebay/documentation-tools/sdks/dotnet and create a new console app project. Add a reference to the eBay.Service DLL, and a few using statements: using eBay.Service.Call; using eBay.Service.Core.Sdk; using eBay.Service.Core.Soap; I'm assuming at this point you've already joined the eBay Developer Network and gotten your app IDs and user tokens. If not: Join the developer program Generate tokens Next, add an app.config file that looks like this: <?xml version="1.0"?> <configuration>   <appSettings>     <add key="Environment.ApiServerUrl" value="https://api.ebay.com/wsapi"/>     <add key="UserAccount.ApiToken" value="YourBigLongToken"/>   </appSettings> </configuration> And then add the code to get the xml list of categories: ApiContext apiContext = GetApiContext(); GetCategoriesCall apiCall = new GetCategoriesCall(apiContext); apiCall.CategorySiteID = "0"; //Leave this commented out to retrieve all category levels (all the way down): //apiCall.LevelLimit = 4; //Uncomment this to begin at a specific parent category: //StringCollection parentCategories = new StringCollection(); //parentCategories.Add("63"); //apiCall.CategoryParent = parentCategories; apiCall.DetailLevelList.Add(DetailLevelCodeType.ReturnAll); CategoryTypeCollection cats = apiCall.GetCategories(); using (StreamWriter outfile = new StreamWriter(@"C:\Temp\EbayCategories.xml")) {    outfile.Write(apiCall.SoapResponse); } GetApiContext() (provided in the sample apps in the SDK) is required for any call:         static ApiContext GetApiContext()         {             //apiContext is a singleton,             //to avoid duplicate configuration reading             if (apiContext != null)             {                 return apiContext;             }             else             {                 apiContext = new ApiContext();                 //set Api Server Url                 apiContext.SoapApiServerUrl = ConfigurationManager.AppSettings["Environment.ApiServerUrl"];                 //set Api Token to access eBay Api Server                 ApiCredential apiCredential = new ApiCredential();                 apiCredential.eBayToken = ConfigurationManager.AppSettings["UserAccount.ApiToken"];                 apiContext.ApiCredential = apiCredential;                 //set eBay Site target to US                 apiContext.Site = SiteCodeType.US;                 return apiContext;             }         } Running this will give you a large (4 or 5 megs) XML file that looks something like this: <soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">    <soapenv:Body>       <GetCategoriesResponse >          <Timestamp>2012-06-06T16:03:46.158Z</Timestamp>          <Ack>Success</Ack>          <CorrelationID>d02dd9e3-295a-4268-9ea5-554eeb2e0e18</CorrelationID>          <Version>775</Version>          <Build>E775_CORE_BUNDLED_14891042_R1</Build> -          <CategoryArray>             <Category>                <BestOfferEnabled>true</BestOfferEnabled>                <AutoPayEnabled>true</AutoPayEnabled>                <CategoryID>20081</CategoryID>                <CategoryLevel>1</CategoryLevel>                <CategoryName>Antiques</CategoryName>                <CategoryParentID>20081</CategoryParentID>             </Category>             <Category>                <BestOfferEnabled>true</BestOfferEnabled>                <AutoPayEnabled>true</AutoPayEnabled>                <CategoryID>37903</CategoryID>                <CategoryLevel>2</CategoryLevel>                <CategoryName>Antiquities</CategoryName>                <CategoryParentID>20081</CategoryParentID>             </Category> (etc.) You could work with this, but I wanted a nicely nested view, like this: <CategoryArray>    <Category Name='Antiques' ID='20081' Level='1'>       <Category Name='Antiquities' ID='37903' Level='2'/> </CategoryArray> ...so I transformed the xml: private void TransformXML(CategoryTypeCollection cats)         {             XmlElement topLevelElement = null;             XmlElement childLevelElement = null;             XmlNode parentNode = null;             string categoryString = "";             XmlDocument returnDoc = new XmlDocument();             XmlElement root = returnDoc.CreateElement("CategoryArray");             returnDoc.AppendChild(root);             XmlNode rootNode = returnDoc.SelectSingleNode("/CategoryArray");             //Loop through CategoryTypeCollection             foreach (CategoryType category in cats)             {                 if (category.CategoryLevel == 1)                 {                     //Top-level category, so we know we can just add it                     topLevelElement = returnDoc.CreateElement("Category");                     topLevelElement.SetAttribute("Name", category.CategoryName);                     topLevelElement.SetAttribute("ID", category.CategoryID);                     rootNode.AppendChild(topLevelElement);                 }                 else                 {                     // Level number will determine how many Category nodes we are deep                     categoryString = "";                     for (int x = 1; x < category.CategoryLevel; x++)                     {                         categoryString += "/Category";                     }                     parentNode = returnDoc.SelectSingleNode("/CategoryArray" + categoryString + "[@ID='" + category.CategoryParentID[0] + "']");                     childLevelElement = returnDoc.CreateElement("Category");                     childLevelElement.SetAttribute("Name", category.CategoryName);                     childLevelElement.SetAttribute("ID", category.CategoryID);                     parentNode.AppendChild(childLevelElement);                 }             }             returnDoc.Save(@"C:\Temp\EbayCategories-Modified.xml");         } Yes, there are probably much cleaner ways of dealing with it, but I'm not an xml expert… Keep in mind, eBay categories do not change on a regular basis, so you should be able to cache this data (either in a file or database) for some time. The xml returns a CategoryVersion node that you can use to determine if the category list has changed. Technorati Tags: Csharp, eBay

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• C#/.NET Little Wonders: Comparer&lt;T&gt;.Default

  - by James Michael Hare

  I’ve been working with a wonderful team on a major release where I work, which has had the side-effect of occupying most of my spare time preparing, testing, and monitoring.  However, I do have this Little Wonder tidbit to offer today. Introduction The IComparable<T> interface is great for implementing a natural order for a data type.  It’s a very simple interface with a single method: 1: public interface IComparer<in T> 2: { 3: // Compare two instances of same type. 4: int Compare(T x, T y); 5: }  So what do we expect for the integer return value?  It’s a pseudo-relative measure of the ordering of x and y, which returns an integer value in much the same way C++ returns an integer result from the strcmp() c-style string comparison function: If x == y, returns 0. If x > y, returns > 0 (often +1, but not guaranteed) If x < y, returns < 0 (often –1, but not guaranteed) Notice that the comparison operator used to evaluate against zero should be the same comparison operator you’d use as the comparison operator between x and y.  That is, if you want to see if x > y you’d see if the result > 0. The Problem: Comparing With null Can Be Messy This gets tricky though when you have null arguments.  According to the MSDN, a null value should be considered equal to a null value, and a null value should be less than a non-null value.  So taking this into account we’d expect this instead: If x == y (or both null), return 0. If x > y (or y only is null), return > 0. If x < y (or x only is null), return < 0. But here’s the problem – if x is null, what happens when we attempt to call CompareTo() off of x? 1: // what happens if x is null? 2: x.CompareTo(y); It’s pretty obvious we’ll get a NullReferenceException here.  Now, we could guard against this before calling CompareTo(): 1: int result; 2:  3: // first check to see if lhs is null. 4: if (x == null) 5: { 6: // if lhs null, check rhs to decide on return value. 7: if (y == null) 8: { 9: result = 0; 10: } 11: else 12: { 13: result = -1; 14: } 15: } 16: else 17: { 18: // CompareTo() should handle a null y correctly and return > 0 if so. 19: result = x.CompareTo(y); 20: } Of course, we could shorten this with the ternary operator (?:), but even then it’s ugly repetitive code: 1: int result = (x == null) 2: ? ((y == null) ? 0 : -1) 3: : x.CompareTo(y); Fortunately, the null issues can be cleaned up by drafting in an external Comparer.  The Soltuion: Comparer<T>.Default You can always develop your own instance of IComparer<T> for the job of comparing two items of the same type.  The nice thing about a IComparer is its is independent of the things you are comparing, so this makes it great for comparing in an alternative order to the natural order of items, or when one or both of the items may be null. 1: public class NullableIntComparer : IComparer<int?> 2: { 3: public int Compare(int? x, int? y) 4: { 5: return (x == null) 6: ? ((y == null) ? 0 : -1) 7: : x.Value.CompareTo(y); 8: } 9: }  Now, if you want a custom sort -- especially on large-grained objects with different possible sort fields -- this is the best option you have.  But if you just want to take advantage of the natural ordering of the type, there is an easier way.  If the type you want to compare already implements IComparable<T> or if the type is System.Nullable<T> where T implements IComparable, there is a class in the System.Collections.Generic namespace called Comparer<T> which exposes a property called Default that will create a singleton that represents the default comparer for items of that type.  For example: 1: // compares integers 2: var intComparer = Comparer<int>.Default; 3:  4: // compares DateTime values 5: var dateTimeComparer = Comparer<DateTime>.Default; 6:  7: // compares nullable doubles using the null rules! 8: var nullableDoubleComparer = Comparer<double?>.Default;  This helps you avoid having to remember the messy null logic and makes it to compare objects where you don’t know if one or more of the values is null. This works especially well when creating say an IComparer<T> implementation for a large-grained class that may or may not contain a field.  For example, let’s say you want to create a sorting comparer for a stock open price, but if the market the stock is trading in hasn’t opened yet, the open price will be null.  We could handle this (assuming a reasonable Quote definition) like: 1: public class Quote 2: { 3: // the opening price of the symbol quoted 4: public double? Open { get; set; } 5:  6: // ticker symbol 7: public string Symbol { get; set; } 8:  9: // etc. 10: } 11:  12: public class OpenPriceQuoteComparer : IComparer<Quote> 13: { 14: // Compares two quotes by opening price 15: public int Compare(Quote x, Quote y) 16: { 17: return Comparer<double?>.Default.Compare(x.Open, y.Open); 18: } 19: } Summary Defining a custom comparer is often needed for non-natural ordering or defining alternative orderings, but when you just want to compare two items that are IComparable<T> and account for null behavior, you can use the Comparer<T>.Default comparer generator and you’ll never have to worry about correct null value sorting again.     Technorati Tags: C#,.NET,Little Wonders,BlackRabbitCoder,IComparable,Comparer

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