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• How to implement Excel Solver functionality in C#?

  - by Vic

  Hi, I have an application in C#, I need to do some optimization calculations, like Excel Solver Add-in does, one option is certainly to write my own solver implementation, but I'm kind of short of time, so I'm looking into libraries that already exist that can help me with this. I've been trying the Microsoft Solver Foundation, which seems pretty neat and cool, the problem is that it doesn't seem to work with the kind of calculations that I need to do. At the end of this question I'm adding the information about the calculations I need to perform and optimize. So basically my question is if any of you know of any other library that I can use for this purpose, or any tutorial that can help to do my own solver, or any idea that gives me a lead to solve this issue. Thanks. Additional Info: This is the data I need to calculate: I have 7 variables, lets call them var1, var2,...,var7 The constraints for these variables are: All of them need to be 0 <= varn <= 0.5 (where n is the number of the variable) The sum of all the variables should be equal to 1 The objective is to maximize the target formula, which in Excel looks like this: (MMULT(TRANSPOSE(L26:L32),M14:M20)) / (SQRT(MMULT(MMULT(TRANSPOSE(L26:L32),M4:S10),L26:L32))) The range that you see in this formula, L26:L32, is actually the range with the variables from above, var1, var2,..., varn. M14:M20 and M4:S10 are ranges with data that I get from different sources, there are more likely decimal values. As I said before, I was using Microsoft Solver Foundation, I modeled pretty much everything with it, I created functions that handle the operations of the target formula, but when I tried to solve the model it always fail, I think it is because of the complexity of the operations. In any case, I just wanted to show these data so you can have an idea about the kind of calculations that I need to implement.

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• How best to use XPath with very large XML files in .NET?

  - by glenatron

  I need to do some processing on fairly large XML files ( large here being potentially upwards of a gigabyte ) in C# including performing some complex xpath queries. The problem I have is that the standard way I would normally do this through the System.XML libraries likes to load the whole file into memory before it does anything with it, which can cause memory problems with files of this size. I don't need to be updating the files at all just reading them and querying the data contained in them. Some of the XPath queries are quite involved and go across several levels of parent-child type relationship - I'm not sure whether this will affect the ability to use a stream reader rather than loading the data into memory as a block. One way I can see of making it work is to perform the simple analysis using a stream-based approach and perhaps wrapping the XPath statements into XSLT transformations that I could run across the files afterward, although it seems a little convoluted. Alternately I know that there are some elements that the XPath queries will not run across, so I guess I could break the document up into a series of smaller fragments based on it's original tree structure, which could perhaps be small enough to process in memory without causing too much havoc. I've tried to explain my objective here so if I'm barking up totally the wrong tree in terms of general approach I'm sure you folks can set me right...

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• DRY Authenticated Tasks in Cocoa (with distributed objects)

  - by arbales

  I'm kind of surprise/infuriated that the only way for me to run an authenticated task, like perhaps sudo gem install shi*t, is to make a tool with pre-written code. I'm writing a MacRuby application, which doesn't seem to expose the KAuthorization* constants/methods. So.. I learned Cocoa and Objective-C. My application creates a object, serves it and calls the a tool that elevates itself and then performs a selector on a distributed object (in the tool's thread). I hoped that the distributed object's methods would evaluated inside the tool, so I could use delegation to create "privileged" tasks. If this won't work, don't try to save it, I just want a DRY/cocoa solution. AuthHelper.m //AuthorizationExecuteWithPrivileges of this. AuthResponder* my_responder = [AuthResponder sharedResponder]; // Gets the proxy object (and it's delegate) NSString *selector = [NSString stringWithUTF8String:argv[3]]; NSLog(@"Performing selector: %@", selector); setuid(0); if ([[my_responder delegate] respondsToSelector:NSSelectorFromString(selector)]){ [[my_responder delegate] performSelectorOnMainThread:NSSelectorFromString(selector) withObject:nil waitUntilDone:YES]; } RandomController.m - (void)awakeFromNib { helperToolPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingString:@"/AuthHelper"]; delegatePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingString:@"/ABExtensions.rb"]; AuthResponder* my_responder = [AuthResponder initAsService]; [my_responder setDelegate:self]; } -(oneway void)install_gems{ NSArray *args = [NSArray arrayWithObjects: @"gem", @"install", @"sinatra", nil]; [NSTask launchedTaskWithLaunchPath:@"/usr/bin/sudo" arguments:args]; NSLog(@"Ran AuthResponder.delegate.install_gems"); // This prints. } ... other privileges tasks. "sudo gem update --system" for one. I'm guessing the proxy object is performing the selector in it's own thread, but I want the current (privileged thread) to do it so I can use sudo. Can I force the distributed object to evaluate the selector on the tool's thread? How else can I accomplish this dryly/cocoaly?

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• ActionScript 3.0: placing code on stage/MC timelines a la AS2 instead of in classes

  - by BoltClock

  I'm aware that ActionScript 3.0 is designed from the ground up to be a largely object-oriented language and using it means less or even no timeline code in Flash documents. I'm quite experienced with OOP and am comfortable writing classes. However, since I mostly use Flash for animations, I hardly ever need to write ActionScript code other than for preloaders, subtitles, quality controls, website links and so on. In fact, I still set my Flash movies to use AS2 to this day because I'm used to gotoAndPlay()/gotoAndStop(), AS2 preloaders, subtitles, quality controls and even getURL(). Of course, I really want to move on now that practically everyone's on Flash Player 9 or 10 and now that I've dabbled with other OO languages like Java, C# and Objective-C too. I'm a complete newcomer to AS3 and am not very learned with AS2 either. Considering my current use of ActionScript, are there any cases where it's still OK to use very simple AS3 code in the timeline instead of moving code to a class, especially since moving to a class might mean unnecessarily increasing the number of LOC from 4 to 40? (Heck, is the latter case ('instead of ...') even a valid concern at all?)

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• Number Algorithm

  - by James

  I've been struggling to wrap my head around this for some reason. I have 15 bits that represent a number. The bits must match a pattern. The pattern is defined in the way the bits start out: they are in the most flush-right representation of that pattern. So say the pattern is 1 4 1. The bits will be: 000000010111101 So the general rule is, take each number in the pattern, create that many bits (1, 4 or 1 in this case) and then have at least one space separating them. So if it's 1 2 6 1 (it will be random): 001011011111101 Starting with the flush-right version, I want to generate every single possible number that meets that pattern. The # of bits will be stored in a variable. So for a simple case, assume it's 5 bits and the initial bit pattern is: 00101. I want to generate: 00101 01001 01010 10001 10010 10100 I'm trying to do this in Objective-C, but anything resembling C would be fine. I just can't seem to come up with a good recursive algorithm for this. It makes sense in the above example, but when I start getting into 12431 and having to keep track of everything it breaks down.

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• Data Binding to an object in C#

  - by Allen

  Objective-c/cocoa offers a form of binding where a control's properties (ie text in a textbox) can be bound to the property of an object. I am trying to duplicate this functionality in C# w/ .Net 3.5. I have created the following very simple class in the file MyClass.cs: class MyClass { private string myName; public string MyName { get { return myName; } set { myName = value; } } public MyClass() { myName = "Allen"; } } I also created a simple form with 1 textbox and 1 button. I init'd one instance of Myclass inside the form code and built the project. Using the DataSource Wizard in Vs2008, i selected to create a data source based on object, and selected the MyClass assembly. This created a datasource entity. I changed the databinding of the textbox to this datasource; however, the expected result (that the textbox's contents would be "allen") was not achieved. Further, putting text into the textbox is not updating the name property of the object. I know i'm missing something fundamental here. At some point i should have to tie my instance of the MyClass class that i initialized inside the form code to the textbox, but that hasn't occurred. Everything i've looked at online seems to gloss over using DataBinding with an object (or i'm missing the mark entirely), so any help is great appreciated. ----Edit--- Utilizing what i learned by the answers, i looked at the code generated by Visual Studio, it had the following: this.myClassBindingSource.DataSource = typeof(BindingTest.MyClass); if i comment that out and substitute : this.myClassBindingSource.DataSource = new MyClass(); i get the expected behavior. Why is the default code generated by VS like it is? Assuming this is more correct than the method that works, how should i modify my code to work within the bounds of what VS generated?

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• What should every developer know about databases?

  - by Aaronaught

  Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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• How to create Dictionary object in AppDelegate to access objectkey in another ViewController

  - by TechFusion

  Hello, I have created Window Based application and tab bar controller as root controller. My objective is to store Text Field data values in one tab bar VC and will be accessible and editable by other VC and also retrievable when application start. I am looking to use NSDictionary class in AppDelegate so that I can access stroed Data Values with keys. //TestAppDelegate.h @interface { ..... .... NSDictionary *Data; } @property (nonatomic, retain) NSDictionary *Data; //TestAppDelegate.m #import "TestAppDelegate.h" NSString *kNamekey =@"Namekey"; NSString *kUserIDkey =@"UserIDkey"; NSString *kPasswordkey =@"Passwordkey"; @implemetation TestAppDelegate @synthesize Data; -(void)applicationDidFinishLaunching:(UIApplication)application { NSString *NameDefault; NSString *UserIDdefault; NSString *Passworddefault; NSString *testvalue = [[NSUserDefaults standardUserDefaults] stringForKey: kNamekey]; if(testvalue == nil) { NSDictionary *appDefaults = [NSDictionary dictionaryWithObjectsAndKeys: NameDefault, kNamekey, UserIdefault kUserIDkey, Passwordefault kPasswordkey, nil]; self.Data = appDefaults; [[NSUserDefaults standardUserDefaults] registerDefaults:appDefaults]; [[NSUserDefaults standardUserDefaults] synchronize]; } else { } } Here ViewController is ViewController of Navigation Controller which is attached with one tab bar.. I have attached xib file with ViewController //ViewController.h @interface IBOutlet UITextField *Name; IBOutlet UITextField *UserId; IBOutlet UITextField *Password; } @property(retain,nonatomic) IBOutlet UITextField *Name @property(retain,nonatomic) IBOutlet UITextField *UserId; @property(retain,nonatomic) IBOutlet UITextField *Password; -(IBAction)Save:(id)sender; @end Here in ViewController.m I want to store Text Field input data with key which are defined in AppDelegate. I have linked Save Barbutton with action. Here I am not getting how to access NSDictionary class with object and keys in ViewController. //ViewController.m -(IBAction)Save:(id)sender{ TestAppDelegate *appDelegate = (TestAppDelegate*)[[UIApplication sharedApplication] delegate]; //Here how to access knamekey here to set object(Name.test) value with key } Please guide me about this. Thanks,

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• Advantages/disadvantages of Python and Ruby

  - by Seburdis

  I know this is going to seem a little like all the other python vs ruby question out there, but I'm not looking specifically to pick one over the other all the time. My question is, essentially, why would you use one language over the other when you are starting a new project? What features does ruby have that python doesn't that would make you decide on it for a given project? What about python over ruby? I was just recently thinking about the differentiation between the two languages because of Jamis Buck's "There is no magic, only awesome" series of articles (4 parts, available here) when I realized I really don't know enough about the two languages to know when to choose one over the other. I'm hoping to get objective answers from people who have experience with both languages, rather than just "python is better, ruby sucks" kind of responses. If you know of a feature in one language that doesn't exist in the other and is great in a certain situation, feel free to chime in and say why you think it's awesome. If you have another language comparable to these that you'd like to suggest pros/cons for, like groovy for example, that would be appreciated too. Some thing I know each language has going for it: Ruby: Awesome metaprogramming Great community Wide selection of Gems Rails Great code readability, usually MacRuby is great for native development on Mac without objc Amazing testing tools (cucumber, rspec, shoulda, autotest, etc.) Python: Whitespace indentation List comprehensions Better functional programming support? Lots of support on linux Easy_install isn't far from gems Great variety of libraries available

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• Using GDataXMLDocument in iPad app

  - by INs

  I'm trying to use GDataXML library in my ipad application. I followed by instructions: Download the gdata-objective-c client library. Unzip the file, navigate to Source\XMLSupport, and drag the two files GDataXMLNode.h and GDataXMLNode.m into your project In XCode, click Project\Edit Project Settings and make sure “All Configurations” are checked. Find the Search Paths\Header Search Paths setting and add /usr/include/libxml2 to the list. Finally, find the Linking\Other Linker Flags section and add -lxml2 to the list. If in code i add #import "GDataXMLNode.h", all is fine. But when i try to use GDataXMLDocument class in my app GDataXMLDocument *doc = [[GDataXMLDocument alloc] initWithData:xmlData options:0 error:nil]; I received the following message: Ld build/Debug-iphonesimulator/DemoApp.app/DemoApp normal i386 cd /Users/svp/Projects/DemoApp setenv MACOSX_DEPLOYMENT_TARGET 10.6 setenv PATH "/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin" /Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/gcc-4.2 -arch i386 -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator4.2.sdk -L/Users/svp/Projects/DemoApp/build/Debug-iphonesimulator -F/Users/svp/Projects/DemoApp/build/Debug-iphonesimulator -filelist /Users/svp/Projects/DemoApp/build/DemoApp.build/Debug-iphonesimulator/DemoApp.build/Objects-normal/i386/DemoApp.LinkFileList -mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -framework Foundation -framework UIKit -framework CoreGraphics -framework MapKit -framework QuartzCore -lxml2.2 -o /Users/svp/Projects/DemoApp/build/Debug-iphonesimulator/DemoApp.app/DemoApp Undefined symbols: "_OBJC_CLASS_$_GDataXMLDocument", referenced from: objc-class-ref-to-GDataXMLDocument in TwitterService.o ld: symbol(s) not found collect2: ld returned 1 exit status Any thoughts?

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• Android : SQL Lite insertion or create table issue

  - by Ram

  Team, can anyone please help me to understand what could be the problem in the below snippet of code? It fails after insertion 2 and insertion 3 debug statements I have the contentValues in the Array list, I am iterating the arraylist and inserting the content values in to the database. Log.d("database","before insertion 1 "); liteDatabase = this.openOrCreateDatabase("Sales", MODE_PRIVATE, null); Log.d("database","before insertion 2 "); liteDatabase .execSQL("Create table activity ( ActivityId VARCHAR,Created VARCHAR,AMTaps_X VARCHAR,AMTemperature_X VARCHAR,AccountId VARCHAR,AccountLocation VARCHAR,AccountName VARCHAR,Classification VARCHAR,ActivityType VARCHAR,COTaps_X VARCHAR,COTemperature_X VARCHAR,Comment VARCHAR,ContactWorkPhone VARCHAR,CreatedByName VARCHAR,DSCycleNo_X VARCHAR,DSRouteNo_X VARCHAR,DSSequenceNo_X VARCHAR,Description VARCHAR,HETaps_X VARCHAR,HETemperature_X VARCHAR,Pro_Setup VARCHAR,LastUpdated VARCHAR,LastUpdatedBy VARCHAR,Licensee VARCHAR,MUTaps_X VARCHAR,MUTemperature_X VARCHAR,Objective VARCHAR,OwnerFirstName VARCHAR,OwnerLastName VARCHAR,PhoneNumber VARCHAR,Planned VARCHAR,PlannedCleanActualDt_X VARCHAR,PlannedCleanReason_X VARCHAR,PrimaryOwnedBy VARCHAR,Pro_Name VARCHAR,ServiceRepTerritory_X VARCHAR,ServiceRep_X VARCHAR,Status VARCHAR,Type VARCHAR,HEINDSTapAuditDate VARCHAR,HEINEmployeeType VARCHAR)"); Log.d("database","before insertion 3 "); int counter = 0; int size = arrayList.size(); for (counter = 0; counter < size; counter++) { ContentValues contentValues = (ContentValues) arrayList .get(counter); liteDatabase.insert("activity", "activityInfo", contentValues); Log.d("database", "Database insertion is done"); } }

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• Getting a variable into another class through properties or button tags with Iphone SDK?

  - by MarcZero

  Hello. I have been pounding my head against a wall trying to figure out what I think is a simple thing to do, but I have, so far, been unable to figure it out with the iPhone SDK. I have a view with 4 buttons. When I push the buttons, I have another view called and come up to take over the screen. I want to have a simple variable passed from the old view to the new view. The purpose of this is to know what button was pressed out of the four identical ones. (trying to get an int value of 1 through 4) Here is what I have tried so far: I initially tried to call the variable from the class itself. My understanding was that my new view was only sitting on top of the old view, so it should not have been released. I could not get access to the variable as the variable was said to not be declared. I then tried to create a method that would return the int value. Again, the view class was not seen and was being declared as a "first use" of it. I then attempted to follow another similar post on here that suggested to try and send the button tag number to some part of the new view. I attempted to do this by setting the new views button title but I still cannot figure out a way to code it without coming up with errors. I am just looking for what method would be the best for me to pursue. I have no problem going back and reading the books on Objective-C, but I'm just trying to figure out which way I should concentrate on. Thank you for any insight.

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• iPhone OS: Strategies for high density image work

  - by Jasconius

  I have a project that is coming around the bend this summer that is going to involve, potentially, an extremely high volume of image data for display. We are talking hundreds of 640x480-ish images in a given application session (scaled to a smaller resolution when displayed), and handfuls of very large (1280x1024 or higher) images at a time. I've already done some preliminary work and I've found that the typical 640x480ish image is just a shade under 1MB in memory when placed into a UIImageView and displayed... but the very large images can be a whopping 5+ MB's in some cases. This project is actually be targeted at the iPad, which, in my Instruments tests seems to cap out at about 80-100MB's of addressable physical memory. Details aside, I need to start thinking of how to move huge volumes of image data between virtual and physical memory while preserving the fluidity and responsiveness of the application, which will be high visibility. I'm probably on the higher ends of intermediate at Objective-C... so I am looking for some solid articles and advice on the following: 1) Responsible management of UIImage and UIImageView in the name of conserving physical RAM 2) Merits of using CGImage over UIImage, particularly for the huge images, and if there will be any performance gain 3) Anything dealing with memory paging particularly as it pertains to images I will epilogue by saying that the numbers I have above maybe off by about 10 or 15%. Images may or may not end up being bundled into the actual app itself as opposed to being loaded in from an external server.

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• Great examples of self-paced labs and exercises

  - by Mayo

  It is probably a safe bet that many of us are what they call Tactile / Kinesthetic Learners meaning that we learn best when we are physically doing something as opposed to listening to an online tutorial or reading a book. My goal with this question is to derive a list of books or online resources that serve as superb examples of self-paced programming labs and exercises. For example, I was extremely impressed with the SportsStore exercise in Steven Sanderson's Pro ASP.NET MVC Framework. The exercise spanned multiple chapters and gradually introduced new topics. I was also impressed with the materials associated with the Windows Azure Boot Camp. The demos and lab materials, accessible through the website, allow us to practice and reinforce what we can read about in articles and books. Please list any examples you might have, one per submission, below. The question is language/platform agnostic. Suggestions can be generic or specific to a given technology (PHP, SQL Server, Azure, Flash, Objective C, etc.). I only ask that the answers pertain to labs and exercises that relate to programming. My hope is that the best answers will float to the top allowing developers to review the top answers and find another programming topic that can be learned through example.

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• VB.NET vs. C#.NET?

  - by Onion-Knight

  Hello everyone, The company I work for has all of its legacy ("legacy" being used rather liberally in this context) code in VB.NET. They have about 6000+ lines of VB.NET code, so all of the developers are comfortable with it. We have started to develop a new product, and are finding that some modules are easier to complete in C# than in VB.NET, such as Interprocess Communication via WCF. The things our product will eventually need to do are as follows: Communicate via IPC between Windows Services, Silverlight, and WinForms Handle parallization, and all the complexity that comes along with it Windows Service and WinForms development ASP.NET, AJAX, and Silverlight development Database (SQL) access Lots of event handling (Sync and Async events) My question is: Given the type of work we will be doing to complete our product, are there features of one language that will make life easier that the other does not have? And if so, it is worth asking the developers to switch to a language they are less comfortable with? I was hoping to keep this as objective as possible, by listing exactly what type of work we will be doing with the product. Please don't turn this into a VB/C# holy war. Thanks, Onion-Knight

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• How can I use "Dependency Injection" in simple php functions, and should I bother?

  - by Tchalvak

  I hear people talking about dependency injection and the benefit of it all the time, but I don't really understand it. I'm wondering if it's a solution to the "I pass database connections as arguments all the time" problem. I tried reading wikipedia's entry on it, but the example is written in Java so I don't solidly understand the difference it is trying to make clear. ( http://en.wikipedia.org/wiki/Dependency_injection ). I read this dependency-injection-in-php article ( http://www.potstuck.com/2009/01/08/php-dependency-injection/ ), and it seems like the objective is to not pass dependencies to an object directly, but to cordon off the creation of an object along with the creation of it's dependencies. I'm not sure how to apply that in a using php functions context, though. Additionally, is the following Dependency Injection, and should I bother trying to do dependency injection in a functional context? Version 1: (the kind of code that I create, but don't like, every day) function get_data_from_database($database_connection){ $data = $database_connection->query('blah'); return $data; } Version 2: (don't have to pass a database connection, but perhaps not dependency injection?) function get_database_connection(){ static $db_connection; if($db_connection){ return $db_connection; } else { // create db_connection ... } } function get_data_from_database(){ $conn = get_database_connection(); $data = $conn->query('blah'); return $data; } $data = get_data_from_database(); Version 3: (the creation of the "object"/data is separate, and the database code is still, so perhaps this would count as dependency injection?) function factory_of_data_set(){ static $db_connection; $data_set = null; $db_connection = get_database_connection(); $data_set = $db_connection->query('blah'); return $data_set; } $data = factory_of_data_set(); Anyone have a good resource or just insight that makes the method and benefit -crystal- clear?

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• Detecting a Dispose() from an exception inside using block

  - by Augusto Radtke

  I have the following code in my application: using (var database = new Database()) { var poll = // Some database query code. foreach (Question question in poll.Questions) { foreach (Answer answer in question.Answers) { database.Remove(answer); } // This is a sample line that simulate an error. throw new Exception("deu pau"); database.Remove(question); } database.Remove(poll); } This code triggers the Database class Dispose() method as usual, and this method automatically commits the transaction to the database, but this leaves my database in an inconsistent state as the answers are erased but the question and the poll are not. There is any way that I can detect in the Dispose() method that it being called because of an exception instead of regular end of the closing block, so I can automate the rollback? I don´t want to manually add a try ... catch block, my objective is to use the using block as a logical safe transaction manager, so it commits to the database if the execution was clean or rollbacks if any exception occured. Do you have some thoughts on that?

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• Suggestions for entering mobile development -- pure iPhone SDK, Andorid SDK. Mono Touch or Titanium?

  - by Tom Cabanski

  I am entering mobile development. I have been working primarily in .NET since 1.0 came out in beta. Before that, I was mostly a C++ and Delphi guy and still dabble in C++ from time to time. I do web apps quite a bit so I am reasonably proficient with Javascript, JQuery and CSS. I have also done a few Java applications. I started web programming with CGI and live mostly in the ASP.NET MVC world these days. I am trying to decide on which platform/OS and tool to select. I am concerned with the size of the market available for my applications as well as the marketibility of the skills I will pick up. The apps I have in mind would work on both phones and pads. Some aspects of what I have in mind will play better on the bigger screens that will be available on pads. Here are the options I am considering: Apple iPhone/iPad using pure Apple SDK (Objective-C) Apple iPhone/iPad using Mono Touch (C#) Android using pure Android SDK (Java) Multiple platforms using something like Titanium to generate native apps from web technologies (HTML, CSS and Javascript) Multiple platforms using HTML5 web applications that run in the browser (HTML, CSS and Javascript). Which option would you choose? Do you have a different suggestion? What are the pros and cons?

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• When optimizing database queries, what exactly is the relationship between number of queries and siz

  - by williamjones

  To optimize application speed, everyone always advises to minimize the number of queries an application makes to the database, consolidating them into fewer queries that retrieve more wherever possible. However, this also always comes with the caution that data transferred is still data transferred, and just because you are making fewer queries doesn't make the data transferred free. I'm in a situation where I can over-include on the query in order to cut down the number of queries, and simply remove the unwanted data in the application code. Is there any type of a rule of thumb on how much of a cost there is to each query, to know when to optimize number of queries versus size of queries? I've tried to Google for objective performance analysis data, but surprisingly haven't been able to find anything like that. Clearly this relationship will change for factors such as when the database grows in size, making this somewhat individualized, but surely this is not so individualized that a broad sense of the landscape can't be drawn out? I'm looking for general answers, but for what it's worth, I'm running an application on Heroku.com, which means Ruby on Rails with a Postgres database.

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• Crazy TableView (Or more likely me being just a jerk) ;-)

  - by Miky Mike

  Hi guy, I'm going crazy with all that objective C. I went to bed at 1.30 pm today, spending the night on my app but I love it... Well that's not the point anyway... My question is .... I have a table view which evaluates a statement when it displays its data : it goes like this : - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"CustomCell"; cell = ((MainCell *)[self.tableView dequeueReusableCellWithIdentifier:CellIdentifier]); if (cell == nil) { [[NSBundle mainBundle] loadNibNamed:@"MainCell" owner:self options:nil]; } Entry *entry = [fetchedResultsController objectAtIndexPath:indexPath]; cell.topLabel.text = [@"* " stringByAppendingString: entry.entryname]; cell.bottomLabel.text = entry.textbody; if ([entry.active boolValue] == YES) { cell.cellImageView.image = [UIImage imageNamed:@"check.png"]; } else { cell.cellImageView.image = nil; cell.accessoryType = UITableViewCellAccessoryDetailDisclosureButton; } return cell; } The problem is that the first time it displays the data, the conditions are met when I scroll down the tableview but when I scroll up, sometimes, I get my "check.png" image and the accessory as well, which is not possible normally. Am I going crazy or is it the tableview ? Could you help me with that please, I can't figure out why it doesn't work... :-(( Thanks a lot in advance. Mike

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• should variable be released or not? iphone-sdk

  - by psebos

  Hi, In the following piece of code (from a book) data is an NSDictionary *data; defined in the header (no property). In the viewDidLoad of the controller the following occurs: - (void)viewDidLoad { [super viewDidLoad]; NSArray *keys = [NSArray arrayWithObjects:@"home", @"work", nil]; NSArray *homeDVDs = [NSArray arrayWithObjects:@"Thomas the Builder", nil]; NSArray *workDVDs = [NSArray arrayWithObjects:@"Intro to Blender", nil]; NSArray *values = [NSArray arrayWithObjects:homeDVDs, workDVDs, nil]; data = [[NSDictionary alloc] initWithObjects:values forKeys:keys]; } Since I am really new to objective-c can someone explain to me why I do not have to retain the variables keys,homeDVDs,workDVDs and values prior exiting the function? I would expect prior the data allocation something like: [keys retain]; [homeDVDs retain]; [workDVDs retain]; [values retain]; or not? Does InitWithObjects copies (recursively) all objects into a new table? Assuming we did not have the last line (data allocation) should we release all the NSArrays prior exiting the function (or we could safely assumed that all NSArrays will be autoreleased since there is no alloc for each one?) Thanks!!!!

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• Getting size of a specific byte array from an array of pointers to bytes

  - by Pat James

  In the following example c code, used in an Arduino project, I am looking for the ability to get the size of a specific byte array within an array of pointers to bytes, for example void setup() { Serial.begin(9600); // for debugging byte zero[] = {8, 169, 8, 128, 2,171,145,155,141,177,187,187,2,152,2,8,134,199}; byte one[] = {8, 179, 138, 138, 177 ,2,146, 8, 134, 8, 194,2,1,14,199,7, 145, 8,131, 8,158,8,187,187,191}; byte two[] = {29,7,1,8, 169, 8, 128, 2,171,145,155,141,177,187,187,2,152,2,8,134,199, 2, 2, 8, 179, 138, 138, 177 ,2,146, 8, 134, 8, 194,2,1,14,199,7, 145, 8,131, 8,158,8,187,187,191}; byte* numbers[3] = {zero, one, two }; function(numbers[1], sizeof(numbers[1])/sizeof(byte)); //doesn't work as desired, always passes 2 as the length function(numbers[1], 25); //this works } void loop() { } void function( byte arr[], int len ) { Serial.print("length: "); Serial.println(len); for (int i=0; i<len; i++){ Serial.print("array element "); Serial.print(i); Serial.print(" has value "); Serial.println((int)arr[i]); } } In this code, I understand that sizeof(numbers1)/sizeof(byte)) doesn't work because numbers1 is a pointer and not the byte array value. Is there a way in this example that I can, at runtime, get at the length of a specific (runtime-determined) byte array within an array of pointers to bytes? Understand that I am limited to developing in c (or assembly) for an Arduino environment. Also open to other suggestions rather than the array of pointers to bytes. The overall objective is to organize lists of bytes which can be retrieved, with length, at runtime.

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• debugging scaffolding contingent upon degbugging boolean (java)

  - by David

  Recently i've found myself writing a lot of methods with what i can only think to call debugging scaffolding. Here's an example: public static void printArray (String[] array, boolean bug) { for (int i = 0; i<array.lenght; i++) { if (bug) System.out.print (i) ; //this line is what i'm calling the debugging scaffolding i guess. System.out.println(array[i]) ; } } in this method if i set bug to true, wherever its being called from maybe by some kind of user imput, then i get the special debugging text to let me know what index the string being printed as at just in case i needed to know for the sake of my debugging (pretend a state of affairs exists where its helpful). All of my questions more or less boil down to the question: is this a good idea? but with a tad bit more objectivity: Is this an effective way to test my methods and debug them? i mean effective in terms of efficiency and not messing up my code. Is it acceptable to leave the if (bug) stuff ; code in place after i've got my method up and working? (if a definition of "acceptability" is needed to make this question objective then use "is not a matter of programing controversy such as ommiting brackets in an if(boolean) with only one line after it, though if you've got something better go ahead and use your definition i won't mind) Is there a more effective way to accomplish the gole of making debugging easier than what i'm doing? Anything you know i mean to ask but that i have forgotten too (as much information as makes sense is appreciated).

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• Scala programming language for beginners, is it a legend?

  - by ali

  Hi every one, I am Ali from Saudi Arabia. undoubtedly, Scala is one of the best programming language for any programmer to learn, but there is "good" problems that is faced especially by beginners, and what seems frustrating that these problems won't solve soon, so as a beginner and on behalf of beginners let me raise these "objective" questions: 1- why scala has no effective and stable development platform, in fact, it suffers many problems with Eclipse, Netbeat, and Intellij. 2- although I have looked for a clear,easy, and understandable explanation of how to get started with Scala, but fortunately, there was no article or guide that deserves to spend the time I have spent to read it. nobody could tell you clear steps that fit you as a beginner who wants to start his"HELLO WORLD" with Scala, while all other languages have its "HELLO WORLD" guides and books. thank you for your time, be sure that you read notes below. 1- I have no experience in programming language before. 2- don't tell me "not to begin with scala", simply, because I will do. 3- OS is windows vista home premium. 4- I hate excuses, such as Scala is new language......etc

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• c++ passing unknown type to a function and any Class type definition

  - by user259789

  I am trying to create a generic class to write and read Objects to/from file. Called it ActiveRecord class only has one method, which saves the class itself: void ActiveRecord::saveRecord(){ string fileName = "data.dat"; ofstream stream(fileName.c_str(), ios::out); if (!stream) { cerr << "Error opening file: " << fileName << endl; exit(1); } stream.write(reinterpret_cast<const char *> (this), sizeof(ActiveRecord)); stream.close(); } now I'm extending this class with User class: class User : public ActiveRecord { public: User(void); ~User(void); string name; string lastName; }; to create and save the user I would like to do something like: User user = User(); user.name = "John"; user.lastName = "Smith" user.save(); how can I get this ActiveRecord::saveRecord() method to take any object, and class definition so it writes whatever i send it: to look like: void ActiveRecord::saveRecord(foo_instance, FooClass){ string fileName = "data.dat"; ofstream stream(fileName.c_str(), ios::out); if (!stream) { cerr << "Error opening file: " << fileName << endl; exit(1); } stream.write(reinterpret_cast<const char *> (foo_instance), sizeof(FooClass)); stream.close(); } and while we're at it, what is the default Object type in c++. eg. in objective-c it's id in java it's Object in AS3 it's Object what is it in C++??

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