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  • What goes into main function?

    - by Woltan
    I am looking for a best practice tip of what goes into the main function of a program using c++. Currently I think two approaches are possible. (Although the "margins" of those approaches can be arbitrarily close to each other) 1: Write a "Master"-class that receives the parameters passed to the main function and handle the complete program in that "Master"-class (Of course you also make use of other classes). Therefore the main function would be reduced to a minimum of lines. #include "MasterClass.h" int main(int args, char* argv[]) { MasterClass MC(args, argv); } 2: Write the "complete" program in the main function making use of user defined objects of course! However there are also global functions involved and the main function can get somewhat large. I am looking for some general guidelines of how to write the main function of a program in c++. I came across this issue by trying to write some unit test for the first approach, which is a little difficult since most of the methods are private. Thx in advance for any help, suggestion, link, ...

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  • What to call factory-like (java) methods used with immutable objects

    - by StaxMan
    When creating classes for "immutable objects" immutable meaning that state of instances can not be changed; all fields assigned in constructor) in Java (and similar languages), it is sometimes useful to still allow creation of modified instances. That is, using an instance as base, and creating a new instance that differs by just one property value; other values coming from the base instance. To give a simple example, one could have class like: public class Circle { final double x, y; // location final double radius; public Circle(double x, double y, double r) { this.x = x; this.y = y; this.r = r; } // method for creating a new instance, moved in x-axis by specified amount public Circle withOffset(double deltaX) { return new Circle(x+deltaX, y, radius); } } So: what should method "withOffset" be called? (note: NOT what its name ought to be -- but what is this class of methods called). Technically it is kind of a factory method, but somehow that does not seem quite right to me, since often factories are just given basic properties (and are either static methods, or are not members of the result type but factory type). So I am guessing there should be a better term for such methods. Since these methods can be used to implement "fluent interface", maybe they could be "fluent factory methods"? Better suggestions? EDIT: as suggested by one of answers, java.math.BigDecimal is a good example with its 'add', 'subtract' (etc) methods. Also: I noticed that there's this question (by Jon Skeet no less) that is sort of related (although it asks about specific name for method)

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  • ReflectionTypeLoadException when I try to run Enable-Migrations with Entity Framework 5.0

    - by Eric Anastas
    I'm trying to use Entity Framework for the first time on one of my projects. I'm using the code first workflow to automatically create my database. Intitaly setting up the database worked fine. Now I'm trying to migrate changes in my classes into the database. The tutorial I'm reading says I need to run "Enable-Migrations" in the package manager console. Yet when I do this I get the following error PM> Enable-Migrations System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information. at System.Reflection.RuntimeModule.GetTypes(RuntimeModule module) at System.Reflection.RuntimeModule.GetTypes() at System.Reflection.Assembly.GetTypes() at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.FindType[TBase](String typeName, Func`2 filter, Func`2 noType, Func`3 multipleTypes, Func`3 noTypeWithName, Func`3 multipleTypesWithName) at System.Data.Entity.Migrations.Design.ToolingFacade.GetContextTypeRunner.RunCore() at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run() Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information. What am I doing wrong? How do I retrieve the loader exceptions property? Also NuGet says I have EF 5.0, but Version property of the EntityFramework item in my project references says 4.4.0.0. I'm not sure if this is related.

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  • Forget late static binding, I need late static __FILE__ ...

    - by bobthecow
    I'm looking for the get_called_class() equivalent for __FILE__ ... Maybe something like get_included_file()? I have a set of classes which would like to know what directory they exist in. Something like this: <?php class A { protected $baseDir; public function __construct() { $this->baseDir = dirname(__FILE__); } public function getBaseDir() { return $this->baseDir; } } ?> And in some other file, in some other folder... <?php class B extends A { // ... } class C extends B { // ... } $a = new A; echo $a->getBaseDir(); $b = new B; echo $b->getBaseDir(); $c = new C; echo $c->getBaseDir(); // Annnd... all three return the same base directory. ?> Now, I could do something ghetto, like adding $this->baseDir = dirname(__FILE__) to each and every extending class, but that seems a bit... ghetto. After all, we're talking about PHP 5.3, right? Isn't this supposed to be the future? Is there another way to get the path to the file where a class was declared?

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  • How to embed revision information using mercurial and maven (and svn)

    - by Zwei Steinen
    Our project had a nice hack (although I'm guessing there are better ways to do it) to embed revision information into the artifacts (jar etc.) when we used svn. Now we have migrated to mercurial, and we want to have a similar thing, but before I start working on a similar hack with mercurial, I wanted to know if there are better ways to do this. Thanks for your answers! <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <executions> <execution> <phase>process-classes</phase> <id>svninfo</id> <goals> <goal>exec</goal> </goals> <configuration> <executable>svn</executable> <arguments> <argument>info</argument> <argument>../</argument> <argument>></argument> <argument>target/some-project/META-INF/svninfo.txt</argument> </arguments> </configuration> </execution> </executions> </plugin>

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  • best web database solution for scala for a high traffic site?

    - by egervari
    I am in charge of a rebuilding a website that gets about 250,000 visitors a day. We'd like to use Scala, but it does not work very well with Spring (in some minor cases) and Hibernate (there is a major and very annoying mismatch here if you want to use scala collections, which we do). The application itself is going to have about 40-50 tables. Other than Hibernate, is there an ORM that works awesome with Scala and is as performant and reliable as Hibernate? Does it also have the same capabilities, or are we going to run into leaky-abstractions if we don't use Hibernate? It would be a big risk for us to go with a framework that is newer and doesn't seem to have a lot of industry backing... and at the same time, Hibernate is a real pain to program against when using Scala. 1) The Java Collection <- Scala Collection is absolutely painful. There is a lot more boilerplate and crap to write. 2) The IDE doesn't import JavaConversions and java interfaces automatically... so we this needs to be done manually. Optimizing Imports in IDEA is going to destroy all the manual work. 3) There is also a performance cost to converting back and forth all the time in your domain objects and your dao classes. 4) Not to mention there needs to be a lot of casting, which produces code ugly as sin. I actually would love to write my own orm that is 100% tailored to scala, but obviously this is really outside of the scope of our project for now. So what is the best approach?

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  • what is the best practice approach for n-tier application development with entity framework?

    - by samsur
    I am building an application using entity framework. I am using the T4 template to generate self tracking entities. Currently, I am thinking of creating the entity framework code in a separate project. In this same project, I would have partial classes with additional methods for the entities. I am thinking of creating a separate project for a service layer (WCF) with methods for the upper/presentation tier. The WCF layer will reference the entity framework project. The methods in the WCF layer will return the entities or accept the entities as the parameters. I am thinkg of creating a third project for the presentation layer (ASP.net), this will make calls to the WCF service but will also need to reference the entities as the WCF methods take these types as the parameters/return types. In short, i want to use the STE entities generated by the T4 template as a DTO to be used in all layers. I was originally thinking of creating a business logic layer that maps to each entities. Example: If i have a customer class, the Business Layer would have a CustomerBLL class and then methods in the customerBLL will be used by the service layer. I was also trying to create a DTO in this business layer. I however found that this approach is very time consuming and i do not see a major benefit as it would create more maintenance work. What is the best practice for n-tier application development using entity framework 4?

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  • Can I write a .NETCF Partial Class to extend System.Windows.Forms.UserControl?

    - by eidylon
    Okay... I'm writing a .NET CF (VBNET 2008 3.5 SP1) application, which has one master form, and it dynamically loads specific UserControls based on menu click, in a sort of framework idea. There are certain methods and properties these controls all need to work within the app. Right now I am doing this as an Interface, but this is aggravating as all get up, because some of the methods are optional, and yet I MUST implement them by the nature of interfaces. I would prefer to use inheritance, so that I can have certain code be inherited with overridability, but if I write a class which inherits System.Windows.Forms.UserControl and then inherit my control from that, it squiggles, and tells me that UserControls MUST inherit directly from System.Windows.Forms.UserControl. (Talk about a design flaw!) So next I thought, well, let me use a partial class to extend System.Windows.Forms.UserControl, but when I do that, even though it all seems to compile fine, none of my new properties/methods show up on my controls. Is there any way I can use partial classes to 'extend' System.Windows.Forms.UserControl? For example, can anyone give me a code sample of a partial class which simply adds a MyCount As Integer readonly property to the System.Windows.Forms.UserControl class? If I can just see how to get this going, I can take it from there and add the rest of my functionality. Thanks in advance! I've been searching google, but can't find anything that seems to work for UserControl extension on .NET CF. And the Interface method is driving me crazy as even a small change means updating ALL the controls whether they need to 'override' the method or not.

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  • How to run a long task in backgroung in iOS applications?

    - by John Canady
    I am developing an application which requires running a task in background. I am trying this by calling a method which will retrieve(download) data from web server through web services. this method will call some more methods which are in different view controller classes. Here when I tap on home button of device, the method is calling but no further execution of the remaining code. This is the code I have written in (void)applicationDidEnterBackground:(UIApplication )application { UIApplication app = [UIApplication sharedApplication]; UIBackgroundTaskIdentifier bgTask = 0; bgTask = [app beginBackgroundTaskWithExpirationHandler:^{ [app endBackgroundTask:bgTask]; bgTask = UIBackgroundTaskInvalid; }]; // Start the long-running task and return immediately. dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ // Do the work associated with the task. NSString *updatekey = [[NSUserDefaults standardUserDefaults] objectForKey:@"updatesetting"]; if([updatekey isEqualToString:@"enabled"]) { DataSettingsView *periodicUpdate = [[DataSettingsView alloc] init]; [periodicUpdate updateDataPeriodically]; //[periodicUpdate viewDidLoad]; //[periodicUpdate release]; } [app endBackgroundTask:bgTask]; bgTask = UIBackgroundTaskInvalid; }); } some one please help me in this background execution of long tasks with some example of code. Some help will appreciated and helpful to me.

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  • overloading "<<" with a struct (no class) cout style

    - by monkeyking
    I have a struct that I'd like to output using either 'std::cout' or some other output stream. Is this possible without using classes? Thanks #include <iostream> #include <fstream> template <typename T> struct point{ T x; T y; }; template <typename T> std::ostream& dump(std::ostream &o,point<T> p) const{ o<<"x: " << p.x <<"\ty: " << p.y <<std::endl; } template<typename T> std::ostream& operator << (std::ostream &o,const point<T> &a){ return dump(o,a); } int main(){ point<double> p; p.x=0.1; p.y=0.3; dump(std::cout,p); std::cout << p ;//how? return 0; } I tried different syntax' but I cant seem to make it work.

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  • What's the correct way to pass parameters from VBScript to COM interface implemented in C#?

    - by nopopem
    I'm trying to expose a fairly simple C# class to COM which should be usable from VBScript (among others). Some objects need to be created via COM calls and will be used in furter calls later on. The definition of the exposed classes and interfaces looks like this: namespace Test { [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)] public interface IComInterface { IFoo CreateFoo(); void UseFoo(int x, IFoo f); } [ClassInterface(ClassInterfaceType.None)] public sealed class CComInterface : IComInterface { public CComInterface() {} public IFoo CreateFoo() { return new Foo(); } public void UseFoo(int x, IFoo f) { f.Bar(); } } [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)] public interface IFoo { void Bar(); } [ClassInterface(ClassInterfaceType.None)] public class Foo : IFoo { internal Foo() {} public void Bar() {} } } The simplest thinkable COM client in VBScript does this: Dim ci Set ci = WScript.CreateObject("Test.CComInterface") Dim foo Set foo = ci.CreateFoo foo.Bar ci.UseFoo 0, foo While the call to Bar succeeds, calling UseFoo fails with "Error 5: invalid procedure call or invalid argument" The generated IDL seems ok to me: dispinterface IComInterface { properties: methods: [id(0x60020003)] IFoo* CreateFoo(); [id(0x60020004)] void UseFoo( [in] long x, [in] IFoo* f); }; The vbs call succeeds when I wrap the second parameter in parentheses like this: ci.UseFoo 0, (foo) As far as I understand (I'm no VBScript expert however) this forces the reference to foo to be passed by value, i.e. a copy of the reference is being made. How can I change the interface so that it can be called with the foo reference directly? Since this will be a public interface used by customers I don't like the idea of having to explain why all the objects created need to be passed back in an extra pair of parentheses...

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  • Hibernate NamingStrategy implementation that maintains state between calls

    - by Robert Petermeier
    Hi, I'm working on a project where we use Hibernate and JBoss 5.1. We need our entity classes to be mapped to Oracle tables that follow a certain naming convention. I'd like to avoid having to specify each table and column name in annotations. Therefore, I'm currently considering implementing a custom implementation of org.hibernate.cfg.NamingStrategy. The SQL naming conventions require the name of columns to have a suffix that is equivalent to a prefix of the table name. If there is a table "T100_RESOURCE", the ID column would have to be named "RES_ID_T100". In order to implement this in a NamingStrategy, the implementation would have to maintain state, i.e. the current class name it is creating the mappings for. It would rely on Hibernate to always call classToTableName() before propertyToColumnName() and to determine all column names by calling propertyToColumnName() before the next call to classToTableName() Is it safe to do that or are there situations where Hibernate will mix things up? I am not thinking of problems through multiple threads here (which can be solved by keeping the last class name in a ThreadLocal) but also of Hibernate deliberately calling this out of order in certain circumstances. For example Hibernate asking for mappings of three properties of class A, then one of class B, then again more attributes of class A.

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  • "Detecting" and loading of "plugins" in GAE

    - by Patrick Cornelissen
    Hi! I have a "plugin like" architecture and I want to create one instance of each class that implements a dedicated interface and put these in a cache. (To have a singleton-ish effect). The plugins will be provided as jars and put into the app engine war file before the app is uploaded. I have tried to use the ClassPathScanningCandidateComponentProvider as I'm using spring anyway, but this didn't work. The provider complained that it was not able to find the HttpServletResponse class file while scanning the classpath. I can't get around this, when I add the servlet jar, then I'll get of course problems, because the same jar is also provided by the GAE. If I don't, I'm getting the error above... So I tried to add a static initialization code, but of course this doesn't work, because the class is initialized when it's instantiated for the first time. (Well I knew that but it was worth a try) The last chance I currently see is that I create a properties file with all plugin classes when the package is created, but this requires writing of a maven plugin etc. and I'd like to avoid that. Is there something that I am missing?

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  • Which is the best license for my Open Source project?

    - by coderex
    I am a web developer, and I don't have enough knowledge about software licenses. I wish to publish some of my works, and I need to select licenses for them. My software product is free of cost. But I have some restrictions on the distribution/modification of the code. It's free of cost (but donations are acceptable ;-)). The source code is freely available. You can use, customize or edit/remove code (as long as the basic nature of the software is not changed). You don't have any permission to change the product name. There are some libraries and classes which are in a folder caller "myname". You don't have the permission to rename "myname". You can contribute any additions or modifications to my project, to the original source repository (the contributors name/email/site link will be listed on the credit file). You can't remove the original author's name from the license. You can put the license file or license code anywhere in the project file or folder. You can redistribute this code as free or commercial software. :) Do you think all these restrictions are valid? Given these restrictions, which license should I use? Edit 1:- My main intention is to make the product more popular with free source code while ensuring the original author is not ignored. The product is open. Edit 2:- Thank you all, the above points are because of my lack of knowledge of license terms. You can help me to correct or remove some of the above points. What I'm basically looking for is in my Edit 1.

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  • .NET binary serialization conditionally without ISerializable

    - by SillyWhy
    I got 2 classes, for example: public class A { private B b; ... } public class B { ... } I need to serialize an object A using BinaryFormatter. When remoting it shall include the field b, but not when serialize to file. Here is what I added: [Serializable] public class A : MarshalByRefObject { private B b; [OnSerializing] private void OnSerializing(StreamingContext context) { if (context.State == StreamingContextStates.File) { this.b = null; } } ... } [Serializable] public class B : MarshalByRefObject { ... } I think this is a bad design because if another class C also contains B, in class C we must add the duplicate OnSerializing() logic as in A. Class B should decide what to do, not class A or C. I don't want to use ISerializable interface because there are too many variables in class B have to be added to SerializationInfo. I can create a SerializationSurrogate for class B, which perform nothing in GetObjectData() & SetObjectData(), then use it when serializing to file. However the same maintenance issue because whoever modify class B can't notice what going to happen during serialization & the existence of SerializationSurrogate. Is there a better alternative?

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  • importing symbols from python package into caller's namespace

    - by Paul C
    I have a little internal DSL written in a single Python file that has grown to a point where I would like to split the contents across a number of different directories + files. The new directory structure currently looks like this: dsl/ __init__.py types/ __init__.py type1.py type2.py and each type file contains a class (e.g. Type1). My problem is that I would like to keep the implementation of code that uses this DSL as simple as possible, something like: import dsl x = Type1() ... This means that all of the important symbols should be available directly in the user's namespace. I have tried updating the top-level __init__.py file to import the relevant symbols: from types.type1 import Type1 from types.type2 import Type2 ... print globals() the output shows that the symbols are imported correctly, but they still aren't present in the caller's code (the code that's doing the import dsl). I think that the problem is that the symbols are actually being imported to the 'dsl' namespace. How can I change this so that the classes are also directly available in the caller's namespace?

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  • Installing Plugins from Cloud p2 repository in Eclipse IDE

    - by user1495036
    I have been recently reading a lot about p2 for a requirement of mine. Most of the p2 documentation online points to p2 for RCP. My requirement is for a plugin repo. I have a plugin that is used within Eclipse IDE. I dnt want to change the repo location but based on the Eclipse Version, if the user looks for Install New Software or Check for Updates it needs to download the respective plugins. My repo currently contains all the plugins for all the versions. but i need to everytime give a different URL to my user based on the Version. For e.g i am using Eclipse 3.7(Indigo). I install the plugin thru Install New Software by adding the p2 Repo URL. Now the user decides to for some requirement move to Eclipse 3.6, I want him to connect to the same p2 Repo URL and download the plugins created for Eclipse 3.6. This is definitely possible using p2 Discovery, or i could categorize the downloads using composite repository but i dnt want to do any of these. Just want to kno is there any API that i can hold on to, so that before processing the URL and finding the updates, i can check the version of Eclipse and redirect it based on the version to an internal URL. This is possible in RCP, want to kno if i can do it in Eclipse p2 UI. All the p2 UI looks to be internal classes. Any directives would be appreciated. Malai

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  • Convert SVG to PDF

    - by Adrian Smith
    How would one go about converting a SVG file to a PDF programatically? (I need to alter the SVG in certain respects before generating the PDF so simply pre-converting it using a tool won't be sufficient.) Ideally using Java but Perl or PHP would be fine too. Obviously I am basically considering Apache FOP and Batik with Java. However no matter how long I search I cannot find a simple introduction on how to do it. Things like SVGConverter have descriptions like "Defines the interface for classes that are able to convert part or all of a GraphicContext", but I don't really know what that means. I have this feeling there must be an API to do this quite simply, provided by FOP or Batik, but I'm just not able to find it at the moment (or perhaps it really doesn't exist.) In terms of the supported SVG features I need, the file has some paths which are filled with some linear gradients. Ideally if I could pass the SVG in as a DOM Document that would be ideal; then I would load my template SVG file, change it as specified by the user, and then generate the PDF.

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  • How to test a C++ library usability in configure.in?

    - by jbatista
    Hi, I'm working on a C++ project and I'm looking for a way to test the existence and usability of IBM Informix's library with the Autotools - namely, editing a configure.in. I don't have experience with Autotools, so basically I'm picking up from the project's configure.in et al. scripts and copying&changing where I feel needs to be changed. IOW, I've been adapting from the existing text in configure.in. So far I've been using successfully the AC_ CHECK_ LIB in configure.in to test whether a certain library both exists and is usable. But this only seems to work with libraries with functions, not e.g. classes. Namely, this fails when testing Informix's libifc++.so: AC_CHECK_LIB(ifc++, ITString, INFORMIX_LIB="-L$INFORMIX_LIB_LOCATION/c++ -lifc++ -L$INFORMIX_LIB_LOCATION -L$INFORMIX_LIB_LOCATION/dmi -L$INFORMIX_LIB_LOCATION/esql -lifdmi -lifsql -lifasf -lifgen -lifos -lifgls -lifglx $INFORMIX_LIB_LOCATION/esql/checkapi.o -lm -ldl -lcrypt -lnsl", echo "* WARNING: libifc++.so not found!" INFORMIX_INC="" INFORMIX_LIB="" ) I've also tried using other combinations, like ITString::ITString, etc. I haven't found a "pure" function in Informix's API (i.e., one that isn't contexted in a C++ class). So I'm hoping that either there's a way to use AC_CHECK_LIB in this context, or there's another autoconf/configure.in "command" for this specific use. Thanks in advance for your feedback.

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  • Inheritence and usage of dynamic_cast

    - by Mewzer
    Hello, Suppose I have 3 classes as follows (as this is an example, it will not compile!): class Base { public: Base(){} virtual ~Base(){} virtual void DoSomething() = 0; virtual void DoSomethingElse() = 0; }; class Derived1 { public: Derived1(){} virtual ~Derived1(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD1DoSomething{ ... } }; class Derived2 { public: Derived2(){} virtual ~Derived2(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD2DoSomething{ ... } }; I want to create an instance of Derived1 or Derived2 depending on some setting that is not available until run-time. As I cannot determine the derived type until run-time, then do you think the following is bad practice?... class X { public: .... void GetConfigurationValue() { .... // Get configuration setting, I need a "Derived1" b = new Derived1(); // Now I want to call the special DoSomething for Derived1 (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething(); } private: Base* b; }; I have generally read that usage of dynamic_cast is bad, but as I said, I don't know which type to create until run-time. Please help!

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  • NSData in CoreData is not saving properly

    - by abisson
    I am currently trying to store images I download from the web into an NSManagedObject class so that I don't have to redownload it every single time the application is opened. I currently have these two classes. Plant.h @property (nonatomic, retain) NSString * name; @property (nonatomic, retain) PlantPicture *picture; PlantPicture.h @property (nonatomic, retain) NSString * bucketName; @property (nonatomic, retain) NSString * creationDate; @property (nonatomic, retain) NSData * pictureData; @property (nonatomic, retain) NSString * slug; @property (nonatomic, retain) NSString * urlWithBucket; Now I do the following: - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { PlantCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath]; Plant *plant = [self.fetchedResultsController objectAtIndexPath:indexPath]; cell.plantLabel.text = plant.name; if(plant.picture.pictureData == nil) { NSLog(@"Downloading"); NSMutableString *pictureUrl = [[NSMutableString alloc]initWithString:amazonS3BaseURL]; [pictureUrl appendString:plant.picture.urlWithBucket]; NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:pictureUrl]]; AFImageRequestOperation *imageOperation = [AFImageRequestOperation imageRequestOperationWithRequest:request success:^(UIImage *image) { cell.plantImageView.image = image; plant.picture.pictureData = [[NSData alloc]initWithData:UIImageJPEGRepresentation(image, 1.0)]; NSError *error = nil; if (![_managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); } }]; [imageOperation start]; } else { NSLog(@"Already"); cell.plantImageView.image = [UIImage imageWithData:plant.picture.pictureData]; } NSLog(@"%@", plant.name); return cell; } The plant information is present, as well as the picture object. However, the NSData itself is NEVER saved throughout the application opening and closing. I always have to REDOWNLOAD the image! Any ideas!? [Very new to CoreData... sorry if it is easy!] thanks!

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  • c# Why can't open generic types be passed as parameters?

    - by Rich Oliver
    Why can't open generic types be passed as parameters. I frequently have classes like: public class Example<T> where T: BaseClass { public int a {get; set;} public List<T> mylist {get; set;} } Lets say BaseClass is as follows; public BaseClass { public int num; } I then want a method of say: public int MyArbitarySumMethod(Example example)//This won't compile Example not closed { int sum = 0; foreach(BaseClass i in example.myList)//myList being infered as an IEnumerable sum += i.num; sum = sum * example.a; return sum; } I then have to write an interface just to pass this one class as a parameter as follows: public interface IExample { public int a {get; set;} public IEnumerable<BaseClass> myIEnum {get;} } The generic class then has to be modified to: public class Example<T>: IExample where T: BaseClass { public int a {get; set;} public List<T> mylist {get; set;} public IEnumerable<BaseClass> myIEnum {get {return myList;} } } That's a lot of ceremony for what I would have thought the compiler could infer. Even if something can't be changed I find it psychologically very helpful if I know the reasons / justifications for the absence of Syntax short cuts.

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  • C++ iterator and const_iterator problem for own container class

    - by BaCh
    Hi there, I'm writing an own container class and have run into a problem I can't get my head around. Here's the bare-bone sample that shows the problem. It consists of a container class and two test classes: one test class using a std:vector which compiles nicely and the second test class which tries to use my own container class in exact the same way but fails miserably to compile. #include <vector> #include <algorithm> #include <iterator> using namespace std; template <typename T> class MyContainer { public: class iterator { public: typedef iterator self_type; inline iterator() { } }; class const_iterator { public: typedef const_iterator self_type; inline const_iterator() { } }; iterator begin() { return iterator(); } const_iterator begin() const { return const_iterator(); } }; // This one compiles ok, using std::vector class TestClassVector { public: void test() { vector<int>::const_iterator I=myc.begin(); } private: vector<int> myc; }; // this one fails to compile. Why? class TestClassMyContainer { public: void test(){ MyContainer<int>::const_iterator I=myc.begin(); } private: MyContainer<int> myc; }; int main(int argc, char ** argv) { return 0; } gcc tells me: test2.C: In member function ‘void TestClassMyContainer::test()’: test2.C:51: error: conversion from ‘MyContainer::iterator’ to non-scalar type ‘MyContainer::const_iterator’ requested I'm not sure where and why the compiler wants to convert an iterator to a const_iterator for my own class but not for the STL vector class. What am I doing wrong?

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  • MEF instance management

    - by Lawrence A. Contreras
    I am working on application that has multiple modules and sub modules. Here's what I need to do: ModuleA has a sub module SubModuleA, SubModuleB, SubModuleC. I want to export ModuleA, SubModuleA, SubModuleB, SubModuleC. ModuleA can have multiple instances. Whenever I import ModuleA inside the sub modules, I want to get the correct instance and also when I import SubModuleA,SubModuleB and SubModuleC inside other classes. How can I manage that scenario using MEF? Do I really need to use MEF. Updated: Here's a quick example: public class School { List<Classroom> classRooms { get; set; } } [Export] public class Classroom { List<Teacher> teachers { get; set; } } public class Teacher { List<Student> students { get; set; } } public class Student { [Import] Classroom classroom { get; set; } } As you can see, I want to export the classroom class because I need to import it in the Student class, let's just say that I really need the classroom class inside the student class. I want to skip the part where we pass the classroom to the teacher and from the teacher we'll pass it to the student. But when I import classroom, I want to have the correct instance where that class room contains the teacher of the student.

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  • Constructor and Destructors in C++ work?

    - by Jack
    I am using gcc. Please tell me if I am wrong - Lets say I have two classes A & B class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; 1) The first line in B's constructor should be a call to A's constructor ( I assume compiler automatically inserts it). Also the last line in B's destructor will be a call to A's destructor (compiler does it again). Why was it built this way? 2) When I say A * a = new B(); compiler creates a new B object and checks to see if A is a base class of B and if it is it allows 'a' to point to the newly created object. I guess that is why we don't need any virtual constructors. ( with help from @Tyler McHenry , @Konrad Rudolph) 3) When I write delete a compiler sees that a is an object of type A so it calls A's destructor leading to a problem which is solved by making A's destructor virtual. As user - Little Bobby Tables pointed out to me all destructors have the same name destroy() in memory so we can implement virtual destructors and now the call is made to B's destructor and all is well in C++ land. Please comment.

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