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  • File IO with Streams - Best Memory Buffer Size

    - by AJ
    I am writing a small IO library to assist with a larger (hobby) project. A part of this library performs various functions on a file, which is read / written via the FileStream object. On each StreamReader.Read(...) pass, I fire off an event which will be used in the main app to display progress information. The processing that goes on in the loop is vaired, but is not too time consuming (it could just be a simple file copy, for example, or may involve encryption...). My main question is: What is the best memory buffer size to use? Thinking about physical disk layouts, I could pick 2k, which would cover a CD sector size and is a nice multiple of a 512 byte hard disk sector. Higher up the abstraction tree, you could go for a larger buffer which could read an entire FAT cluster at a time. I realise with today's PC's, I could go for a more memory hungry option (a couple of MiB, for example), but then I increase the time between UI updates and the user perceives a less responsive app. As an aside, I'm eventually hoping to provide a similar interface to files hosted on FTP / HTTP servers (over a local network / fastish DSL). What would be the best memory buffer size for those (again, a "best-case" tradeoff between perceived responsiveness vs. performance).

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  • Generating python wrapper for 3ed party c++ dll using swig with

    - by MuraliK
    I am new bee to swig. I have a third party c++ dll with the following functions export. I want to call these dll functions in python. So thought of using swig to generate the wrapper using swig. I am not sure what sort of wrapper i need to generate (do i need to generate .lib or .dll to use it in python?). In case i need to generate .dll how do i do that using visual studio 2010. There are some call back function like SetNotifyHandler(void (__stdcall * nf)(int wp, void *lp)) in the bellow list. How do define such function in interface file. can someone help me plese? enter code here #ifndef DLL_H #define DLL_H #ifdef DLL_BUILD #define DLLFUNC __declspec(dllexport) #else #define DLLFUNC __declspec(dllimport) #endif #pragma pack(push) #pragma pack(1) #pragma pack(pop) extern "C" { DLLFUNC int __stdcall StartServer(void); DLLFUNC int __stdcall GetConnectionInfo(int connIndex, Info *buf); DLLFUNC void __stdcall SetNotifyWindow(HWND nw); DLLFUNC void __stdcall SetNotifyHandler(void (__stdcall * nf)(int wp, void *lp)); DLLFUNC int __stdcall SendCommand(int connIndex, Command *cmd); };

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  • Cocoa button won't display image

    - by A Mann
    Just started exploring Cocoa so pretty much a total noob. I've written a very simple game. Set it up in Interface Builder and got it working fine. It contains a number of buttons and I'm now trying to get the buttons to display images. To start with I'm trying to get an image displayed on just one of the buttons which is called tile0 . The image file (it's nothing but a green square at the moment, but I'm just trying to get that working before I attempt anything more exotic) is sitting in the same directory as the class file which controls the game. I have the following code sitting in my wakeFromNib method: NSString *myImageFileName = [[NSString alloc] init]; myImageFileName = @"greenImage.jpg"; NSImage *myImage = [[NSImage alloc] initByReferencingFile:myImageFileName]; [tile0 setImage: myImage]; Trouble is, the game runs fine, but the image isn't appearing on my button. Is there someone who could kindly tell me if I'm doing something obviously wrong? Many Thanks.

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  • Error with custom Class definition in protocol

    - by Greg
    I'm trying to set up a custom delegate protocol and am getting a strange error that I don't understand. I wonder if someone could point out what I'm doing wrong here (I'm still new to Ob-C and protocol use)... The situation is that I've built my own URLLoader class to manage loading and parsing data from the internet. I'm now trying to set up a protocol for delegates to implement that will respond to the URLLoader's events. So, below is my protocol... #import <UIKit/UIKit.h> #import "URLLoader.h" /** * Protocol for delegates that will respond to a load. */ @protocol URLLoadResponder <NSObject> - (void)loadDidComplete:(URLLoader *)loader; - (void)loadDidFail:(URLLoader *)loader withError:(NSString *)error; @end However, I'm getting the following error for both method signatures: Expected ')' before 'URLLoader' I feel like I must be overlooking something small and silly. Any help folks could offer would be greatly appreciated! Whoops ... it was pointed out that I should include URLLoader.h. Here it is: #import <Foundation/Foundation.h> #import "URLLoadResponder.h" /** * URLLoader inferface. */ @interface URLLoader : NSObject { NSString *name; NSString *loadedData; NSMutableData *responseData; NSObject *delegate; BOOL _isLoaded; } @property (nonatomic, retain) NSString *name; @property (nonatomic, retain) NSString *loadedData; @property (nonatomic, retain) NSObject *delegate; - (void)loadFromURL:(NSString *)url; - (void)addCompleteListener:(id)observer selector:(SEL)sel; - (void)removeCompleteListener:(id)observer; - (void)parseLoadedData:(NSString *)data; - (void)complete; - (void)close; - (BOOL)isLoaded; + (NSURL *)makeUrlWithString:(NSString *)url; + (URLLoader *)initWithName:(NSString *)name; @end

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  • Python/Sqlite app for web or desktop?

    - by ChrisC
    I am in the planning stages of rewriting an Access db I wrote several years ago in a full fledged program. I have very slight experience coding, but not enough to call myself a programmer by far. I'll definitely be learning as I go, so I'd like to keep everything as simple as possible. I've decided on Python and SQLite for my program, but I need help on my next decision. Here is my situation 1) It'll be a desktop program, run locally on each machine, all Windows 2) I want a nice looking GUI with colors, different shaped buttons, nice menus, lists, etc, etc 3) I'm thinking about using a browser interface because (a) from what I've read, browser apps can look really great, and (b) I understand there are lots of free tools to assist in setting up the GUI/GUI code with drag and drop tools, so that helps my "keep it simple" goal. 4) I want the program to be totally portable so it runs completely from one single folder on a user's PC. If I do go the browser app router, a major concern I have is the possibility that a user's browser settings could affect or break the app. How likely is this? What other pros and cons are there for my situation?

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  • NSMutableArray for Object which has NSString property causes memory leak

    - by user262325
    Hello everyone I hope to add objects to a NSMutableArray "myArray", The NSMutableArray is the array for FileObj which has a NSString property "fileName" #import <UIKit/UIKit.h> @interface FileObj : NSObject { NSString *fileName; } -(void) setfileName:(NSString *)s ; -(NSString *) getfileName ; @end // // File.m// #import "File.h" @implementation FileObj -(void) setfileName:(NSString *)s ; { fileName=s; } -(NSString *) getfileName ; { return fileName; } @end I initialize the myArray here: NSMutableArray *temarray; temarray=[[NSMutableArray alloc] init]; self.myArray=temarray; [temarray release]; the codes to add object to myArray FileObj *newobj=[[FileObj alloc]init ]; NSString *fieldValue2 = [[NSString alloc] initWithUTF8String:@"aaaa"]; [newobj setfileName:fieldValue2]; [myArray addObject:newobj]; [fieldValue2 release]; //**if I enabled the line, it will cause crash** //**if I disable the line, it will cause memory leak** [newobj release]; Welcome any comment Thanks interdev

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  • Casting pointer to object to void * in C++

    - by JB
    I've been reading StackOverflow too much and started doubting all the code I've ever written, I keep thinking "Is that undefined behavour?" even in code that has been working for ages. So my question - Is it safe and well defined behavour to cast a pointer to an object (In this case abstract interface classes) to a void* and then later on cast them back to the original class and call method using them? I'm fully aware that the code that does this is probably awful. I wouldn't even consider writing it like this now (this is old code which I don't really want to change), so I'm not looking for a discussion of better ways to do this. I already know how to write it better if I ever did this again. But if it's actually broken to rely on this in C++ then I'll have to look at changing the code, if it's merely awful code then changing it won't be a priority. I would have had no doubts about something this simple a year or two ago but as my understanding of C++ increases I actually find I have more and more worries about code being safe under the standards even if it works perfectly well. Perhaps reading too much stack overflow is a bad thing for productivity sometimes :P

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  • Should I *always* import my file references into the database in drupal?

    - by sprugman
    I have a cck type with an image field, and a unique_id text field. The file name of the image is based on the unique_id. All of the content, including the image itself is being generated automatically via another process, and I'm parsing what that generates into nodes. Rather than creating separate fields for the id and the image, and doing an official import of the image into the files table, I'm tempted to only create the id field and create the file reference in the theme layer. I can think of pros and cons: 1) Theme Layer Approach Pros: makes the import process much less complex don't have to worry about syncing the db with the file system as things change more flexible -- I can move my images around more easily if I want Cons: maybe not as much The Drupal Way™ not as pure -- I'll wind up with more logic on the theme side. 2) Import Approach Pros: import method is required if we ever wanted to make the files private (we won't.) safer? Maybe I'll know if there's a problem with the image at import time, rather than view time. Since I'll be bulk importing, that might make a difference. if I delete a node through the admin interface, drupal might be able to delete the file for me, as well. Con: more complex import and maintenance All else being equal, simpler is always better, so I'm leaning toward #1. Are there any other issues I'm missing? (Since this is an open ended question, I guess I'll make it a community wiki, whatever that means.)

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  • Large Switch statements: Bad OOP?

    - by Mystere Man
    I've always been of the opinion that large switch statements are a symptom of bad OOP design. In the past, I've read articles that discuss this topic and they have provided altnerative OOP based approaches, typically based on polymorphism to instantiate the right object to handle the case. I'm now in a situation that has a monsterous switch statement based on a stream of data from a TCP socket in which the protocol consists of basically newline terminated command, followed by lines of data, followed by an end marker. The command can be one of 100 different commands, so I'd like to find a way to reduce this monster switch statement to something more manageable. I've done some googling to find the solutions I recall, but sadly, Google has become a wasteland of irrelevant results for many kinds of queries these days. Are there any patterns for this sort of problem? Any suggestions on possible implementations? One thought I had was to use a dictionary lookup, matching the command text to the object type to instantiate. This has the nice advantage of merely creating a new object and inserting a new command/type in the table for any new commands. However, this also has the problem of type explosion. I now need 100 new classes, plus I have to find a way to interface them cleanly to the data model. Is the "one true switch statement" really the way to go? I'd appreciate your thoughts, opinions, or comments.

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  • Packaging Java apps for the Windows/Linux desktop.

    - by alexmcchessers
    I am writing an application in Java for the desktop using the Eclipse SWT library for GUI rendering. I think SWT helps Java get over the biggest hurdle for acceptance on the desktop: namely providing a Java application with a consistent, responsive interface that looks like that belonging to any other app on your desktop. However, I feel that packaging an application is still an issue. OS X natively provides an easy mechanism for wrapping Java apps in native application bundles, but producing an app for Windows/Linux that doesn't require the user to run an ugly batch file or click on a .jar is still a hassle. Possibly that's not such an issue on Linux, where the user is likely to be a little more tech-savvy, but on Windows I'd like to have a regular .exe for him/her to run. Has anyone had any experience with any of the .exe generation tools for Java that are out there? I've tried JSmooth but had various issues with it. Is there a better solution before I crack out Visual Studio and roll my own? Edit: I should perhaps mention that I am unable to spend a lot of money on a commercial solution.

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  • Same Origin issue with web service call

    - by Wjdavis5
    My web server runs at http://mypc.com:80 ` Given the following snip: $(window).load(function () { var myURL = "http://mypc.com:8000/PSOCharts/service/HighChart_ColumnChart/i"; $.getJSON(myURL) .done(function(data) {alert(data);}); }); I am running to this error: XMLHttpRequest cannot load http://mypc.com:8000/PSOCharts/service/HighChart_ColumnChart/i. Origin http://mypc.com is not allowed by Access-Control-Allow-Origin. I understand why (I think) b/c my webservice runs at port 8000 which is different from what IIS is running on (port 80). I thought I could get around by using jsonp (according to the jQuery documentation here So I copied the example of making a call to the flickr api, but it isnt working. Any thoughts/sugggestions? UPDATE Ok so my request is being made now: var myURL = "http://192.168.1.104:8000/PSOCharts/service/HighChart_ColumnChart/i?jsoncallback=?"; $.ajax({ url :myURL, dataType: "jsonp", success: function(data) {a(data)} , error: function(){alert("err");}, }); But I am continually hitting the error function, here is what's being returned: [1.4,54.43,49.39,93.23] Now I'm assuming this is b/c the response text doesnt contain any type of callback here is the part of the interface I'm calling: [WebInvoke(Method = "GET", RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, UriTemplate = "HighChart_ColumnChart/{id}?callback={cb}")] List<double> HighChart_ColumnChart(string id,string cb); Here is the actual function being called: public List<double> HighChart_ColumnChart(string id,string cb) { var z = new List<double>(); z.Add(1.4); z.Add(54.43); z.Add(49.39); z.Add(93.23); return z; } when I debug, the CB param is something like : "jQuery19108121746340766549_1372630643878". How do I modify the code to wrap it correctly? Thanks for the help thus far!

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  • How to implement iterator as an attribute of a class in Java

    - by de3
    Hi, let's say I have this simple MyArray class, with two simple methods: add, delete and an iterator. In the main method we can see how it is supposed to be used: public class MyArray { int start; int end; int[] arr; myIterator it; public MyArray(){ this.start=0; this.end=0; this.arr=new int[500]; it=new myIterator(); } public void add(int el){ this.arr[this.end]=el; this.end++; } public void delete(){ this.arr[this.start]=0; this.start++; } public static void main(String[] args){ MyArray m=new MyArray(); m.add(3); m.add(299); m.add(19); m.add(27); while(m.it.hasNext()){ System.out.println(m.it.next()); } } And then MyIterator should be implemented somehow: import java.util.Iterator; public class myIterator implements Iterator{ @Override public boolean hasNext() { // TODO Auto-generated method stub return false; } @Override public Object next() { // TODO Auto-generated method stub return null; } @Override public void remove() { // TODO Auto-generated method stub } } MyIterator should iterate arr from MyArray class, from start to end values; both are also attributes of MyArray. So, as MyIterator should use MyArray attributes, how should MyIterator be implemented? Perhaps I can send the current object in the initialization: it=new myIterator(this); But I guess it's not the best soultion. Or maybe MyArray itself should implement Iterator interface? How is this solved?

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  • C# generics with MVVM, pulling the T out of <T>

    - by bufferz
    My Model is a generic class that contains a (for example) Value property which can be int, float, string, bool, etc. So naturally this class is represented something like Model<T>. For the sake of collections Model<T> implements the interface IModel, although IModel is itself empty of any content. My ViewModel contains and instance of Model<T> and it is passed in through ViewModel's constructor. I still want to know what T is in ViewModel, so when I expose Model to the View I know the datatype of Model's buried Value property. The class for ViewModel ends up looking like the following: class ViewModel<T> { private Model<T> _model; public ViewModel(Model<T> model) { ....blah.... } public T ModelsValue {get; set; } } This works fine, but is limited. So now I need to expose a collection of IModels with varying Ts to my View, so I'm trying to set up an ObservableCollection of new ViewModel<T>s to a changing list of IModels. The problem is, I can't figure out how to get T from Model<T> from IModel to construct ViewModel<T>(Model<T>) at runtime. In the VS2010 debugger I can mouseover any IModel object and see its full Model<int> for example at runtime so I know the data is in there. Any ideas?

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  • What do you call a generalized (non-GUI-related) "Model-View-Controller" architecture?

    - by dcuccia
    I am currently refactoring code that coordinates multiple hardware components for data acquisition, and feeling a bit like I'm recreating the wheel. In particular, an MVC-like pattern seems to be emerging. Except, this has nothing to do with a GUI and I'm worried that I'm forcing this particular pattern where another might be more appropriate. Here's my scenario: Individual hardware "component" classes obey interface contracts for each hardware type. Previously, component instances were orchestrated by a single monolithic InstrumentController class, which relied heavily on configuration + branching logic for executing a specific acquisition sequence. After an iteration, I have a separate controller for each component, with these controllers all managed by a small InstrumentControllerBase (or its derivatives). The composite system will receive "input" either programmatically or via inter-hardware component triggering - in either case these interactions are routed to, and handled by, the appropriate controller. So, I have something that feels MVC-esque, but I don't know if that's because I'm forcing the point. With little direct MVC experience in application development, it's hard to know if I'm just trying to make my scenario fit MVC, where another pattern might be a good alternative or complimentary. My problem is, search results and wiki documentation of these family of patterns seems to immediately drop me into GUI-specific discussions. I understand "M means Model data and the V means View" - but do you call the superset pattern? Component-Commander-Controller? Whence can I exhume examples exemplary?

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  • MEF: Satisfy part on an Export using and Export from the composed part.

    - by Pop Catalin
    Hi, I have the following scenario in Silverlight 4: I have a notifications service Snippet [InheritedExport] public interface INotificationsService : IObservable<ReceivedNotification> { void IssueNotifications(IEnumerable<ClientIssuedNotification> notifications); } and and implementation of this service Snippet [PartCreationPolicy(CreationPolicy.NonShared)] public class ClientNotificationService : INotificationsService { [Import] IPlugin Plugin { get; set; } ... } How can I say to MEF that the Plugin property of the ClientNotificationService must be provided by the importing class that imports the INotificationsService. For example: Snippet public class Client { [Export] IPlugin Current { get; set; } [Import] INotificationService NotificationService; } How can I say that I want MEF to satisfy the ClientNotificationService.Plugin part with the exported IPlugin by the Client class. Basically I want the NotificationService, to receive a Unique ID provided by the importing class, whenever it is created and composed to a new class, or if there's and alternative method, like using meta data to do this I'd appreciate any insights. I've been struggling with this for a while. Thanks

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  • How can I split abstract testcases in JUnit?

    - by Willi Schönborn
    I have an abstract testcase "AbstractATest" for an interface "A". It has several test methods (@Test) and one abstract method: protected abstract A unit(); which provides the unit under testing. No i have multiple implementations of "A", e.g. "DefaultA", "ConcurrentA", etc. My problem: The testcase is huge (~1500 loc) and it's growing. So i wanted to split it into multiple testcases. How can organize/structure this in Junit 4 without the need to have a concrete testcase for every implementation and abstract testcase. I want e.g. "AInitializeTest", "AExectueTest" and "AStopTest". Each being abstract and containing multiple tests. But for my concrete "ConcurrentA", i only want to have one concrete testcase "ConcurrentATest". I hope my "problem" is clear. EDIT Looks like my description was not that clear. Is it possible to pass a reference to a test? I know parameterized tests, but these require static methods, which is not applicable to my setup. Subclasses of an abstract testcase decide about the parameter.

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  • Undeclared - 'first use in function'

    - by Ragunath Jawahar
    I'm new to Objective-C, though I have a very good hand in Android. I'm trying to make a call to a method but it gives me 'first use in function'. I know I'm making a silly mistake but experts could figure it out easily. RootViewController.h #import <UIKit/UIKit.h> #import "ContentViewController.h" @interface RootViewController : UITableViewController { ContentViewController *contentViewController; } @property (nonatomic, retain) ContentViewController *contentViewController; - (NSString*)getContentFileName:(NSString*)title; //<--- This function declartion @end RootViewController.m #import "RootViewController.h" #import "HAWATAppDelegate.h" #import "ContentViewController.h" @implementation RootViewController @synthesize contentViewController; ... more methods ... #pragma mark - #pragma mark Table view delegate - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { HAWATAppDelegate *appDelegate = (HAWATAppDelegate *)[[UIApplication sharedApplication] delegate]; NSString *title = (NSString *) [appDelegate.titles objectAtIndex:indexPath.row]; NSString *fileName = getContentFileName:title; //<--- Here is the error ... } - (NSString*) getContentFileName:(NSString*)title { return [title lowercaseString]; } @end There must be a simple thing I'm missing. Please let me know. Thanks in advance.

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  • How to Sort a TreeList in Sitecore 6 in the Source

    - by Scott
    My team uses Sitecore 6 as content management system and then .Net to interface with Sitecore API. In many of our templates we make use of a Treelist. When adding a new item to the selected items Treelist it automatically puts the item at the bottom of the list. In some lists they get very large. In most cases end users would like to see these lists sorted descending by a Date field that is part of the templates that can be added as selected to the Treelist. Programmatically on the .Net side its very easy to handle this using Linq OrderByDescending and all displays great in the site to visitors. What I am trying to figure out is how to get it to display the same in Sitecore Content Editor. I've not found anything from Google search other than there seems to be a SortBy you can specify in the source but I tried this and can't get it to have any effect. Has anyone dealt with this before? Again, main goal is to sort items in a Treelist in the Sitecore Content Editor itself. Thanks for any input anyone has.

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  • How to create a separate thread to do some operation periodically and update UI in WPF?I'm stack

    - by black sensei
    Hello Experts! I'm trying to do a periodic separated thread operation let's say check for internet connection or check for user's info via web service and update the user interface. i've tried with quartz.net to implement that.So i created an inner class for the window i need to update.That inner class does what is meant for but the problem is that i don't know how to access parent's(window class) members form the child(inner class). for example public partial class Window2 : Window { private int i; public Window2() { InitializeComponent(); } public string doMyOperation() { //code here return result; } public class Myclass :IJob { public void Execute(JobExecutionContext context) { string result = doMyOperation(); //Now here i could be able to call a label of name lblNotif //lblNotif.Content = result; } } } Well the whole idea works but i'm stacked at here i need to access a controls of Window2 Since i'm stacked i tried Spring.Net way of implementing Quartz hoping that i could use MethodInvokingJobDetailFactoryObject and rather have the Operation done on Window2 itself.But for some reason i'm having an exception Cannot resolve type [System.Windows.Window2,System.Windows];, could not load type from string value System.Windows.Window2,System.Windows and the wiring is done so <object name="UpdateLabelJob" type="System.Windows.Window2,System.Windows"/> What i'm i doing wrong here?Is that a way round? thanks for reading and for helping out

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  • How do I pull `static final` constants from a Java class into a Clojure namespace?

    - by Joe Holloway
    I am trying to wrap a Java library with a Clojure binding. One particular class in the Java library defines a bunch of static final constants, for example: class Foo { public static final int BAR = 0; public static final int SOME_CONSTANT = 1; ... } I had a thought that I might be able to inspect the class and pull these constants into my Clojure namespace without explicitly def-ing each one. For example, instead of explicitly wiring it up like this: (def *foo-bar* Foo/BAR) (def *foo-some-constant* Foo/SOME_CONSTANT) I'd be able to inspect the Foo class and dynamically wire up *foo-bar* and *foo-some-constant* in my Clojure namespace when the module is loaded. I see two reasons for doing this: A) Automatically pull in new constants as they are added to the Foo class. In other words, I wouldn't have to modify my Clojure wrapper in the case that the Java interface added a new constant. B) I can guarantee the constants follow a more Clojure-esque naming convention I'm not really sold on doing this, but it seems like a good question to ask to expand my knowledge of Clojure/Java interop. Thanks

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  • memory leak when removing objects in NSMutableArray

    - by user262325
    Hello everyone I hope to store MYFileObj to NSMutableArray (fileArray) and display data on an UITavleView(tableview). //----------------------------------MYFileObj #import <UIKit/UIKit.h> @interface MYFileObj : NSObject { NSString *fileName; } -(void) setFileName:(NSString *)s ; -(NSString *) fileName ; @end the array I want to store data NSMutableArray *fileArray; I created new object and add to fileArray MYFileObj *newobj=[[MYFileObj alloc] init ]; NSString *ss=[[NSString alloc] initWithFormat:@"%@",path] ; [newobj setFileName:ss]; [ss release]; [fileArray addObject:newobj]; [newobj release]; [atableview reloadData]; After the first time relaodData and do something, I want to reload fileArray and redraw atableview. //code to remove all object in atableview if([fileArray count]>0) { [fileArray removeAllObjects]; [atableview reloadData]; } I notice that there are memory leak. I hope to know the method "removeAllObjects" removes only MYFileObj themselves or also removes MYFileObj's member property "fileName"? Thanks interdev

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  • Database (MySQL) structuring: pros and cons of multiple tables

    - by Gideon
    I am collecting data and storing it MySQL, for: 75 variables 55 countries Each year I have, at this stage since I am building this tool created a single table, of variables / countries (storing 1 year worth of data). Next year (and for several years after that) a new set of data will be input for each country. There are therefore 3 variables in controlling data returned to a user reviewing all collected data. The general form of any query would be: Show me these specifics variables, for these specific countries, for these specific years. (Show me average age and weight, for USA and Canada, for 2012 and 2009, for example) My question is, it seems that I have two options for arranging this data: -Multiple tables where I create a table of country / variable for each year data is collected - Single table and simply add a column (field) for the year that data relates to. As far as I can tell I could make these database calls with either sructure, but is one more powerful / efficient / quicker, and why? Thanks for your consideration. It's a PDO / PHP interface if that is relevent.

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  • How is covariance cooler than polymorphism...and not redundant?

    - by P.Brian.Mackey
    .NET 4 introduces covariance. I guess it is useful. After all, MS went through all the trouble of adding it to the C# language. But, why is Covariance more useful than good old polymorphism? I wrote this example to understand why I should implement Covariance, but I still don't get it. Please enlighten me. using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Sample { class Demo { public delegate void ContraAction<in T>(T a); public interface IContainer<out T> { T GetItem(); void Do(ContraAction<T> action); } public class Container<T> : IContainer<T> { private T item; public Container(T item) { this.item = item; } public T GetItem() { return item; } public void Do(ContraAction<T> action) { action(item); } } public class Shape { public void Draw() { Console.WriteLine("Shape Drawn"); } } public class Circle:Shape { public void DrawCircle() { Console.WriteLine("Circle Drawn"); } } public static void Main() { Circle circle = new Circle(); IContainer<Shape> container = new Container<Circle>(circle); container.Do(s => s.Draw());//calls shape //Old school polymorphism...how is this not the same thing? Shape shape = new Circle(); shape.Draw(); } } }

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  • Wouldn't it be nice to have a type variable referring to the class's instance.

    - by user93197
    I often have a pattern like this: class VectorBase<SubClass, Element> where SubClass : VectorBase<SubClass, Element>, new() where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(); result.data = newData; return result; } } class VectorInt : VectorBase<VectorInt, Int32> { } class MyInt : Addable<MyInt> { int data; public MyInt(int data) { this.data = data; } public MyInt add(MyInt t) { return new MyInt(data + t.data); } } interface Addable<T> { T add(T t); } But I would rather just have: class VectorBase2<Element> where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(data); return result; } } class VectorInt2 : VectorBase2<Int32> { } Why not make the subclass type available to all classes? Is this technically impossible?

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  • HTML , Jquery Fisheye menu

    - by Thirumalai
    I have used the fisheye jquery "interface.js" I want to make make 3rd element with id="default" should be show default like mouse over effect , Please help me thaks in advance <div class="dock" id="dock1"> <div class="dock-container2"> <a class="dock-item2" href="#" ><span>E-Mail</span><img src="images/ui/img1.png" alt="home" width="40"/></a> <a class="dock-item2" href="#"><span>Contact</span><img src="images/ui/img2.png" alt="contact" width="50" /></a> <a class="dock-item2" href="#" id="default"><span>Car</span><img src="images/ui/img3.png" alt="portfolio" width="60"/></a> <a class="dock-item2" href="#"><span>Home</span><img src="images/ui/img4.png" alt="music" width="70" /></a> <a class="dock-item2" href="#"><span>Air Line</span><img src="images/ui/img5.png" alt="video" width="80" /></a> <a class="dock-item2" href="#"><span>Train</span><img src="images/ui/img6.png" alt="history" width="70"/></a> <a class="dock-item2" href="#"><span>Hotel</span><img src="images/ui/img7.png" alt="calendar" width="60"/></a> <a class="dock-item2" href="#"><span>Links</span><img src="images/ui/img8.png" alt="links" width="50"/></a> <a class="dock-item2" href="#"><span>Call Us</span><img src="images/ui/img9.png" alt="rss" width="40" /></a> </div> $(document).ready(function () { $('#dock1').Fisheye({ maxWidth: 60, items: 'a', itemsText: 'span', container: '.dock-container2', itemWidth: 40, proximity: 80, alignment: 'left', valign: 'top', halign: 'center' }); $("#pagecontent").slider(); });

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