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• Is it possible to restrict instantiation of an object to only one other (parent) object in VB.NET?

  - by Casey

  VB 2008 .NET 3.5 Suppose we have two classes, Order and OrderItem, that represent some type of online ordering system. OrderItem represents a single line item in an Order. One Order can contain multiple OrderItems, in the form of a List(of OrderItem). Public Class Order Public Property MyOrderItems() as List(of OrderItem) End Property End Class It makes sense that an OrderItem should not exist without an Order. In other words, an OrderItem class should not be able to be instantiated on its own, it should be dependent on an Order class to contain it and instantiate it. However, the OrderItem should be public in scope so that it's properties are accessible to other objects. So, the requirements for OrderItem are: Can not be instantiated as a stand alone object; requires Order to exist. Must be public so that any other object can access it's properties/methods through the Order object. e.g. Order.OrderItem(0).ProductID. OrderItem should be able to be passed to other subs/functions that will operate on it. How can I achieve these goals? Is there a better approach?

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• garbage collector Issue

  - by Eslam

  this question is like my previous one Given: 3. interface Animal { void makeNoise(); } 4. class Horse implements Animal { 5. Long weight = 1200L; 6. public void makeNoise() { System.out.println("whinny"); } 7. } 8. public class Icelandic extends Horse { 9. public void makeNoise() { System.out.println("vinny"); } 10. public static void main(String[] args) { 11. Icelandic i1 = new Icelandic(); 12. Icelandic i2 = new Icelandic(); 13. Icelandic i3 = new Icelandic(); 14. i3 = i1; i1 = i2; i2 = null; i3 = i1; 15. } 16. } When line 14 is reached, how many objects are eligible for the garbage collector? A. 0 B. 1 C. 2 D. 3 E. 4 F. 6 i choosed A but the right answer is E, but i don't know Why?

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• Put together tiles in android sdk and use as background

  - by Jon

  In a feeble attempt to learn some Android development am I stuck at graphics. My aim here is pretty simple: Take n small images and build a random image, larger than the screen with possibility to scroll around. Have an animated object move around on it I have looked at the SDK examples, Lunar Lander especially but there are a few things I utterly fail to wrap my head around. I've got a birds view plan (which in my head seems reasonably sane): How do I merge the tiles into one large image? The background is static so I figure I should do like this: Make a 2d array with refs to the tiles Make a large Drawable and draw the tiles on it At init draw this big image as the background At each onDraw redraw the background of the previous spot of the moving object, and the moving object at its new location The problem is the hands on things. I load the small images with "Bitmap img1 = BitmapFactory.decodeResource (res, R.drawable.img1)", but then what? Should I make a canvas and draw the images on it with "canvas.drawBitmap (img1, x, y, null);"? If so how to get a Drawable/Bitmap from that? I'm totally lost here, and would really appreciate some hands on help (I would of course be grateful for general hints as well, but I'm primarily trying to understand the Graphics objects). To make you, dear reader, see my level of confusion will I add my last desperate try: Drawable drawable; Canvas canvas = new Canvas (); Bitmap img1 = BitmapFactory.decodeResource (res, R.drawable.img1); // 50 x 100 px image Bitmap img2 = BitmapFactory.decodeResource (res, R.drawable.img2); // 50 x 100 px image canvas.drawBitmap (img1, 0, 0, null); canvas.drawBitmap (img2, 50, 0, null); drawable.draw (canvas); // obviously wrong as draw == null this.setBackground (drawable); Thanks in advance

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• grabbing layer contents in a class

  - by Mike

  I have a custom UIImageView class that creates thumbnails (UIImageView) and each thumbnail has a label. The label is created by another class. The label class creates a UIImageView and a UITextView on top of it. This is the init object class' init method: - (id)initWithFrame:(CGRect)frame { if ([super initWithFrame:frame] == nil) { return nil; } CGRect myFrame = CGRectMake(0, 0, 100, 100); myLabel = [[myLabelClass alloc] initWithFrame: myFrame]; //myLabelClass is a UIImageView based class [myLabel setCenter:CGPointMake(50, 50)]; [self addSubview: myLabel]; return self; } So, I have this MAIN VIEW CONTROLLER | |___ UIImageView WITH LABEL | |____ label background (UIView) |____ UITEXTVIEW (text) Now I want to write the contents of all these 3 components to a quartz context. I need to write using drawInRect, because I need to write the full object to a precise location. I expected object.layer.contents to be the image equivalent to these 3 "layers" flattened, in other words, the object's image, the label background and the label text, as it would if I created these 3 objects in Photoshop and flatten the composition. I also expect object.myLabel.layer.contents to contains the rendered contents of the UITextView over the label background. The problem is that when I use UIImage *myImage = [UIImage imageWithCGImage:objecto.myLabel.layer.contents]; [myImage drawInRect:CGRectMake(0, 0, 100, 100)]; I get nothing. How can I obtain a "flattened" image resultant to the full object (including its subviews)? thanks

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• NSCollectionView: Can the same object not be in the array more than once or is this a bug?

  - by Sean

  I may be doing this all wrong, but I thought I was on the right track until I hit this little snag. Basically I was putting together a toy using NSCollectionView and trying to understand how to hook that all up using IB. I have a button which will add a couple of strings to the NSArrayController: The first time I press this button, my strings appear in the collection view as expected: The second time I press the button, the views scroll down and room is made - but the items don't appear to get added. I just see blank space: The button is implemented as follows (controller is a pointer to the NSArrayController I added in IB): - (IBAction)addStuff:(id)control { [controller addObjects:[NSArray arrayWithObjects:@"String 1",@"String 2",@"String 3",nil]]; } I'm not sure what I'm doing wrong. Rather than try to explain all the connections/binds/etc, if you need more info, I'd be grateful if you could just take a quick look at the toy project itself. UPDATE: After more experimentation as suggested by James Williams, it seems the problem stems from having multiple objects with the same memory address in the array. This confuses either NSArrayController or NSCollectionView (not sure which). Changing my addStuff: to this resulted in the behavior I originally expected: [controller addObjects:[NSArray arrayWithObjects:[NSMutableString stringWithString:@"String 1"],[NSMutableString stringWithString:@"String 2"],[NSMutableString stringWithString:@"String 3"],nil]]; So the question now, I guess, is if this is a bug I should report to Apple or if this is intended/documented behavior and I just missed it?

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• The perfect web UI framework (with Microsoft stack?) - architecture question?

  - by Igorek

  I'm looking for suggestions for the following issue, and I realize there is really not going to be a perfect answer to my question: I have a UI built in WinForms.NET (v4.0 framework) with WCF back-end and EF4 model objects, that I am looking to port to the web. UI is not huge and is not super complex and is structured well. But it is not a super simple system either. I am looking to pick a technology stack for the web-frontend that will target desktop & partially mobile platforms, provide a good development platform to build on, and facilitate code reuse across UI and back-end tiers... I would rather avoid: custom coding of UI-centric scripts, because they are hard to debug, non-compiled, usually a maintenance nightmare, almost always start to contain business logic, and duplicate some of the logic that back-end tiers have (especially validation) custom-coding for Desktop Web and Mobile Web UI's separately (although I realize that mobile web UI will likely contain fewer of data-entry screens and more reporting screens) non-.NET technology stacks I would love to: target the reporting capabilities of the system toward mobile web browsers not have to write a single line of script (javascript, jquery, etc.) utilize a good collection of controls that produces an elegant UI use .NET for everything The way I see it right now, I need to re-write this app in Silverlight, utilize a 3rd party UI framework like Telerik, and re-do the reports UI again for mobile platforms separately. However, I'm rather concerned about the shelf-life of Silverlight and the needed to deploy a different architecture to deal with mobile platform. Is there an ASP.NET/MVC/Ajax architecture/framework/library that would allow me to get at the power of .NET and without painful (imho) client-side scripting, while providing a decent user experience Thank you

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• Android NDK import-module / code reuse

  - by Graeme

  Morning! I've created a small NDK project which allows dynamic serialisation of objects between Java and C++ through JNI. The logic works like this: Bean - JavaCInterface.Java - JavaCInterface.cpp - JavaCInterface.java - Bean The problem is I want to use this functionality in other projects. I separated out the test code from the project and created a "Tester" project. The tester project sends a Java object through to C++ which then echo's it back to the Java layer. I thought linking would be pretty simple - ("Simple" in terms of NDK/JNI is usually a day of frustration) I added the JNIBridge project as a source project and including the following lines to Android.mk: NDK_MODULE_PATH=.../JNIBridge/jni/" JNIBridge/jni/JavaCInterface/Android.mk: ... include $(BUILD_STATIC_LIBRARY) JNITester/jni/Android.mk: ... include $(BUILD_SHARED_LIBRARY) $(call import-module, JavaCInterface) This all works fine. The C++ files which rely on headers from JavaCInterface module work fine. Also the Java classes can happily use interfaces from JNIBridge project. All the linking is happy. Unfortunately JavaCInterface.java which contains the native method calls cannot see the JNI method located in the static library. (Logically they are in the same project but both are imported into the project where you wish to use them through the above mechanism). My current solutions are are follows. I'm hoping someone can suggest something that will preserve the modular nature of what I'm trying to achieve: My current solution would be to include the JavaCInterface cpp files in the calling project like so: LOCAL_SRC_FILES := FunctionTable.cpp $(PATH_TO_SHARED_PROJECT)/JavaCInterface.cpp But I'd rather not do this as it would lead to me needing to update each depending project if I changed the JavaCInterface architecture. I could create a new set of JNI method signatures in each local project which then link to the imported modules. Again, this binds the implementations too tightly.

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• Overriding content_type for Rails Paperclip plugin

  - by Fotios

  I think I have a bit of a chicken and egg problem. I would like to set the content_type of a file uploaded via Paperclip. The problem is that the default content_type is only based on extension, but I'd like to base it on another module. I seem to be able to set the content_type with the before_post_process class Upload < ActiveRecord::Base has_attached_file :upload before_post_process :foo def foo logger.debug "Changing content_type" #This works self.upload.instance_write(:content_type,"foobar") # This fails because the file does not actually exist yet self.upload.instance_write(:content_type,file_type(self.upload.path) end # Returns the filetype based on file command (assume it works) def file_type(path) return `file -ib '#{path}'`.split(/;/)[0] end end But...I cannot base the content type on the file because Paperclip doesn't write the file until after_create. And I cannot seem to set the content_type after it has been saved or with the after_create callback (even back in the controller) So I would like to know if I can somehow get access to the actual file object (assume there are no processors doing anything to the original file) before it is saved, so that I can run the file_type command on that. Or is there a way to modify the content_type after the objects have been created.

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• ListBox selector odd behavior when there are dupes

  - by byte1918

  I'm working on a bigger project atm, but I made this simple example to show you what happens.. using System.Collections.Generic; using System.Windows; namespace txt { public partial class MainWindow { public MainWindow() { InitializeComponent(); } private void Window_Loaded(object sender, RoutedEventArgs e) { var obsLst = new List<Info> { new Info { name = "asd" }, new Info { name = "asd" }, new Info { name = "asd" }, new Info { name = "asd" } }; var temp = new List<Info>(); for (var i = 1; i <= 3; i++) { temp.Add(obsLst[0]); //I add 3 of the same item from obsLst to temp } lst.DataContext = temp; //lst = ListBox } } public class Info { public string name { get; set; } } } The ListBox ItemsSource is set to {Binding}.. When I start the application I get 3 txt.Info objects displayed and if I click any of them, 2 or even all of them get selected aswell. From my understanding the problem relies in the fact that the listbox selector cannot differentiate between the items and therefor doesn't know which one I selected. Here's a picture of what it looks like.. I only clicked on the second txt.Info item. I found a solution where someone said that I have to specify the DisplayMemberPath, but I can't really do that in the other project because I have a datatemplate for the object. Any ideas on how I could fix this would be great.. Thx in advance.

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• How do I declare "Member Fields" in Java?

  - by Bub

  This question probably reveals my total lack of knowledge in Java. But let me first show you what I thought was the correct way to declare a "member field": public class NoteEdit extends Activity { private Object mTitleText; private Object mBodyText; I'm following a google's notepad tutorial for android (here) and they simply said: "Note that mTitleText and mBodyText are member fields (you need to declare them at the top of the class definition)." I thought I got it and then realized that this little snippet of code wasn't working. if (title != null) { mTitleText.setText(title); } if (body != null) { mBodyText.setText(body); } So either I didn't set the "member fields" correctly which I thought all that was needed was to declare them private Objects at the top of the NoteEdit class or I'm missing something else. Thanks in advance for any help.UPDATE I was asked to show where these fields were being intialized here is another code snippet hope that it's helpful... @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.note_edit); Long mRowId; mTitleText = (EditText) findViewById(R.id.title); mBodyText = (EditText) findViewById(R.id.body);

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• Return type from DAL class (Sql ce, Linq to Sql)

  - by bretddog

  Hi, Using VS2008 and Sql CE 3.5, and preferably Linq to Sql. I'm learning database, and unsure about DAL methods return types and how/where to map the data over to my business objects: I don't want direct UI binding. A business object class UserData, and a class UserDataList (Inherits List(Of UserData)), is represented in the database by the table "Users". I use SQL Compact and run SqlMetal which creates dbml/designer.vb file. This gives me a class with a TableAttribute: <Table()> _ Partial Public Class Users I'm unsure how to use this class. Should my business object know about this class, such that the DAL can return the type Users, or List(Of Users) ? So for example the "UserDataService Class" is a part of the DAL, and would have for example the functions GetAll and GetById. Will this be correct : ? Public Class UserDataService Public Function GetAll() As List(Of Users) Dim ctx As New MyDB(connection) Dim q As List(Of Users) = From n In ctx.Users Select n Return q End Function Public Function GetById(ByVal id As Integer) As Users Dim ctx As New MyDB(connection) Dim q As Users = (From n In ctx.Users Where n.UserID = id Select n).Single Return q End Function And then, would I perhaps have a method, say in the UserDataList class, like: Public Class UserDataList Inherits List(Of UserData) Public Sub LoadFromDatabase() Me.clear() Dim database as New UserDataService dim users as List(Of Users) users = database.GetAll() For each u in users dim newUser as new UserData newUser.Id = u.Id newUser.Name = u.Name Me.Add(newUser) Next End Sub End Class Is this a sensible approach? Would appreciate any suggestions/alternatives, as this is my first attempt on a database DAL. cheers!

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• How to write Java-like enums in C++ ?

  - by Rahul G

  Coming from Java background, I find C++'s enums very lame. I wanted to know how to write Java-like enums (the ones in which the enum values are objects, and can have attributes and methods) in C++. As an example, translate the following Java code (a part of it, sufficient to demonstrate the technique) to C++ : public enum Planet { MERCURY (3.303e+23, 2.4397e6), VENUS (4.869e+24, 6.0518e6), EARTH (5.976e+24, 6.37814e6), MARS (6.421e+23, 3.3972e6), JUPITER (1.9e+27, 7.1492e7), SATURN (5.688e+26, 6.0268e7), URANUS (8.686e+25, 2.5559e7), NEPTUNE (1.024e+26, 2.4746e7); private final double mass; // in kilograms private final double radius; // in meters Planet(double mass, double radius) { this.mass = mass; this.radius = radius; } private double mass() { return mass; } private double radius() { return radius; } // universal gravitational constant (m3 kg-1 s-2) public static final double G = 6.67300E-11; double surfaceGravity() { return G * mass / (radius * radius); } double surfaceWeight(double otherMass) { return otherMass * surfaceGravity(); } public static void main(String[] args) { if (args.length != 1) { System.err.println("Usage: java Planet <earth_weight>"); System.exit(-1); } double earthWeight = Double.parseDouble(args[0]); double mass = earthWeight/EARTH.surfaceGravity(); for (Planet p : Planet.values()) System.out.printf("Your weight on %s is %f%n", p, p.surfaceWeight(mass)); } } Any hep would be greatly appreciated! Thanks!

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• Loading an XML configuration file BEFORE the flex application loads

  - by Shahar

  Hi, We are using an XML file as an external configuration file for several parameters in our application (including default values for UI components and properties values of some service layer objects). The idea is to be able to load the XML configuration file before the flex application initializes any of its components. This is crucial because XML loading is processed a-synchronously in flex, which can potentially cause race-conditions in the application. For example: the configuration file holds the endpoint URL of a web service used to obtain data from the server. The URL resides in the XML because we want to allow our users to alter the endpoint URL according to their environment. Now because the endpoint URL is retrieved only after the XML has been completely loaded, some of the application's components might be invoking operations on this web service before it is initialized with the correct endpoint. The trivial solution would have been to suspend the initialization of the application until the complete event is dispatched by the loader. But it appears that this solution is far from being trivial. I haven't found a single solution that allows me to load the XML before any other object in the application. Can anyone advice or comment on this matter? Regards, Shahar

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• Upgraded to Xcode 4 -- Endless stream of duplicate symbol errors causing build errors

  - by D-Nice

  Everything was working perfectly fine in Xcode 3 yesterday before I upgraded. So I completed the upgrade, restarted my computer, and opened my old project. I had to reconfigure a few settings like the header paths so that I could begin to compile. I'm using AdWhirl for ad mediation, and at this point my errors begin to read something like duplicate symbol _OBJC_METACLASS_$_SBJSON in /Users/Admin/Desktop/TMapLiteAdwhirl/AdWhirl/MMSDK/libMMSDK.a(SBJSON.o) and /Users/Admin/Library/Developer/Xcode/DerivedData/TruxMapLite-bgpylibztethnlhkfkdumpvrjvgy/Build/Intermediates/TruxMapLite.build/Debug-iphoneos/TruxMapLite.build/Objects-normal/armv6/SBJSON.o for architecture armv6 The library it's referring to is the SDK for one of the ad networks I'm including in AdWhirl. Both of the 'duplicate symbols' refer to the SAME FILE, but they use different paths. If I had still had XCode 3, I would simply try excluding these libraries from the build path, but I have no idea how that can be done in Xcode 4. I've tried everything all the way down to deleting the library and all associated files from my project, but when I do this, i will simply get the same type of error for a different library in the AdWhirl directory. This is incredibly frustrating because before my upgrade everything was working smoothly and I was prepared to submit my binary. If anyone has any advice, id be more than happy to give it a try. Thanks!

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• datareader.close is called in if - else branching. How to validate datareader is actually closed usi

  - by tanmay

  Hi, I have written couple of custom rules in for fxcop 1.36. I have written a code to find weather opened datareader is closed or not. But it does not check which datareader object is calling the close() method so I can't be sure if all opened datareader objs are closed!! 2nd: if I am using data reader in IF else like if 1=2 dr = cmd.executeReader(); else dr = cmd2.execureReader(); end if in this case it will search for 2 datareader objects to be closed.. I am putting my code for more clarity. public override ProblemCollection Check(Member member) { Method method = member as Method; int countCatch =0; int countErrLog = 0; Instruction objInstr = null; if (method != null) { for (int i = 0; i < method.Instructions.Count; i++) { objInstr = method.Instructions[i]; if (objInstr.Value != null) { if (objInstr.Value.ToString().Contains("System.Data.SqlClient.SqlDataReader")) { countCatch += 1; } if (countCatch>0) { if (objInstr.Value.ToString().Contains("System.Data.SqlClient.SqlDataReader.Close")) { countErrLog += 1; } } } } } if (countErrLog!=countCatch) { Resolution resolu = GetResolution(new string[] { method.ToString() }); Problems.Add(new Problem(resolu)); } return Problems; Thanks and regards, Tanmay.

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• Reduce function calls

  - by Curious2learn

  Hello, I profiled my python program and found that the following function was taking too long to run. Perhaps, I can use a different algorithm and make it run faster. However, I have read that I can also possibly increase the speed by reducing function calls, especially when it gets called repeatedly within a loop. I am a python newbie and would like to learn how to do this and see how much faster it can get. Currently, the function is: def potentialActualBuyers(setOfPeople,theCar,price): count=0 for person in setOfPeople: if person.getUtility(theCar) >= price and person.periodCarPurchased==None: count += 1 return count where setOfPeople is a list of person objects. I tried the following: def potentialActualBuyers(setOfPeople,theCar,price): count=0 Utility=person.getUtility for person in setOfPeople: if Utility(theCar) >= price and person.periodCarPurchased==None: count += 1 return count This, however, gives me an error saying local variable 'person' referenced before assignment Any suggestions, how I can reduce function calls or any other changes that can make the code faster. Again, I am a python newbie and even though I may possibly be able to use a better algorithm, it is still worthwhile learning the answer to the above question. Thanks very much.

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• Comparison operators not supported for type IList when Paging data in Linq to Sql

  - by Dan

  I can understand what the error is saying - it can't compare a list. Not a problem, other than the fact that I don't know how to not have it compare a list when I want to page through a model with a list as a property. My Model: Event : IEvent int Id string Title // Other stuff.. LazyList<EventDate> Dates // The "problem" property Method which pages the data (truncated): public JsonResult JsonEventList(int skip, int take) { var query = _eventService.GetEvents(); // Do some filtering, then page data.. query = query.Skip(skip).Take(take); return Json(query.ToArray()); } As I said, the above is truncated quite a bit, leaving only the main point of the function: filter, page and return JSON'd data. The exception occurs when I enumerate (.ToArray()). The Event object is really only used to list the common objects of all the event types (Meetings, Birthdays, etc - for example). It still implements IEvent like the other types, so I can't just remove the LazyList<EventDate> Dates' property unless I no longer implementIEvent` Anyway, is there a way to avoid this? I don't really want to compare a LazyList when I page, but I do not know how to resolve this issue. Thank you in advance! :)

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• Node & Redis: Crucial Design Issues in Production Mode

  - by Ali

  This question is a hybrid one, being both technical and system design related. I'm developing the backend of an application that will handle approx. 4K request per second. We are using Node.js being super fast and in terms of our database struction we are using MongoDB, with Redis being a layer between Node and MongoDB handling volatile operations. I'm quite stressed because we are expecting concurrent requests that we need to handle carefully and we are quite close to launch. However I do not believe I've applied the correct approach on redis. I have a class Student, and they constantly change stages(such as 'active', 'doing homework','in lesson' etc. Thus I created a Redis DB for each state. (1 for being 'active', 2 for being 'doing homework'). Above I have the structure of the 'active' students table; xa5p - JSON stringified object #1 pQrW - JSON stringified object #2 active_student_table - {{studentId:'xa5p'}, {studentId:'pQrW'}} Since there is no 'select all keys method' in Redis, I've been suggested to use a set such that when I run command 'smembers' I receive the keys and later on do 'get' for each id in order to find a specific user (lets say that age older than 15). I've been also suggested that in fact I used never use keys in production mode. My question is, no matter how 'conceptual' it is, what specific things I should avoid doing in Node & Redis in production stage?. Are they any issues related to my design? Students must be objects and I sure can list them in a list but I haven't done yet. Is it that crucial in production stage?

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• How to test method call order with Moq

  - by Finglas

  At the moment I have: [Test] public void DrawDrawsAllScreensInTheReverseOrderOfTheStack() { // Arrange. var screenMockOne = new Mock<IScreen>(); var screenMockTwo = new Mock<IScreen>(); var screens = new List<IScreen>(); screens.Add(screenMockOne.Object); screens.Add(screenMockTwo.Object); var stackOfScreensMock = new Mock<IScreenStack>(); stackOfScreensMock.Setup(s => s.ToArray()).Returns(screens.ToArray()); var screenManager = new ScreenManager(stackOfScreensMock.Object); // Act. screenManager.Draw(new Mock<GameTime>().Object); // Assert. screenMockOne.Verify(smo => smo.Draw(It.IsAny<GameTime>()), Times.Once(), "Draw was not called on screen mock one"); screenMockTwo.Verify(smo => smo.Draw(It.IsAny<GameTime>()), Times.Once(), "Draw was not called on screen mock two"); } But the order in which I draw my objects in the production code does not matter. I could do one first, or two it doesn't matter. However it should matter as the draw order is important. How do you (using Moq) ensure methods are called in a certain order? Edit I got rid of that test. The draw method has been removed from my unit tests. I'll just have to manually test it works. The reversing of the order though was taken into a seperate test class where it was tested so it's not all bad. Thanks for the link about the feature they are looking into. I sure hope it gets added soon, very handy.

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• Difference in BackgroundWorker thread access in VS2010 / .NET 4.0?

  - by Jonners

  Here's an interesting one - in VS2005 / VS2008 running against .NET 2.0 / .NET 3.0 / .NET 3.5, a BackgroundWorker thread may not directly update controls on a WinForms form that initiated that thread - you'll get a System.InvalidOperationException out of the BackgroundWorker stating "Cross-thread operation not valid: Control 'thecontrol' accessed from a thread other than the thread it was created on". I remember hitting this back in 2004 or so when I first started writing .NET WinForms apps with background threads. There are several ways around the problem - this is not a question asking for that answer. I've been told recently that this kind of operation is now allowed when written in VS2010 / .NET 4.0. This seems unlikely to me, since this kind of object access restriction has always been a fairly fundamental part of thread-safe programming. Allowing a BackgroundWorker thread direct access to objects owned not by itself but by its parent UI form seems contrary to that principle. A trawl through the .NET 4.0 docs hasn't revealed any obvious changes that could account for this behaviour. I don't have VS2010 / .NET 4.0 to test this out - does anyone who has access to that toolset know for sure whether the model has changed to allow that kind of thread interaction? I'd like to either take advantage of it in future, or deploy the cluestick. ;)

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• How is a functional programming-based javascript app laid out?

  - by user321521

  I've been working with node.js for awhile on a chat app (I know, very original, but I figured it'd be a good learning project). Underscore.js provides a lot of functional programming concepts which look interesting, so I'd like to understand how a functional program in javascript would be setup. From my understanding of functional programming (which may be wrong), the whole idea is to avoid side effects, which are basically having a function which updates another variable outside of the function so something like var external; function foo() { external = 'bar'; } foo(); would be creating a side effect, correct? So as a general rule, you want to avoid disturbing variables in the global scope. Ok, so how does that work when you're dealing with objects and what not? For example, a lot of times, I'll have a constructor and an init method that initializes the object, like so: var Foo = function(initVars) { this.init(initVars); } Foo.prototype.init = function(initVars) { this.bar1 = initVars['bar1']; this.bar2 = initVars['bar2']; //.... } var myFoo = new Foo({'bar1': '1', 'bar2': '2'}); So my init method is intentionally causing side effects, but what would be a functional way to handle the same sort of situation? Also, if anyone could point me to either a python or javascript source code of a program that tries to be as functional as possible, that would also be much appreciated. I feel like I'm close to "getting it", but I'm just not quite there. Mainly I'm interested in how functional programming works with traditional OOP classes concept (or does away with it for something different if that's the case).

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• Hibernate: Walk millions of rows and don't leak memory

  - by Autocracy

  The below code functions, but Hibernate never lets go of its grip of any object. Calling session.clear() causes exceptions regarding fetching a joined class, and calling session.evict(currentObject) before retrieving the next object also fails to free the memory. Eventually I exhaust my heap space. Checking my heap dumps, StatefulPersistenceContext is the garbage collector's root for all references pointing to my objects. public class CriteriaReportSource implements JRDataSource { private ScrollableResults sr; private Object currentObject; private Criteria c; private static final int scrollSize = 10; private int offset = 1; public CriteriaReportSource(Criteria c) { this.c = c; advanceScroll(); } private void advanceScroll() { // ((Session) Main.em.getDelegate()).clear(); this.sr = c.setFirstResult(offset) .setMaxResults(scrollSize) .scroll(ScrollMode.FORWARD_ONLY); offset += scrollSize; } public boolean next() { if (sr.next()) { currentObject = sr.get(0); if (sr.isLast()) { advanceScroll(); } return true; } return false; } public Object getFieldValue(JRField jrf) throws JRException { Object retVal = null; if(currentObject == null) { return null; } try { retVal = PropertyUtils.getProperty(currentObject, jrf.getName()); } catch (Exception ex) { Logger.getLogger(CriteriaReportSource.class.getName()).log(Level.SEVERE, null, ex); } return retVal; } }

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• Is it possible to create a python iterator over pre-defined mutable data?

  - by Wilduck

  I might be doing this wrong, if I am, let me know, but I'm curious if the following is possible: I have a class that holds a number of dictionaries, each of which pairs names to a different set of objects of a given class. For example: items = {"ball" : ItemInstance1, "sword" : ItemInstance2} people = {"Jerry" : PersonInstance1, "Bob" : PersonInstance2, "Jill" : PersonInstance3} My class would then hold the current items and people that are availible, and these would be subject to change as the state changes: Class State: def __init__(self, items, people): self.items = items self.people = people I would like to define a iter() and next() method such that it iterates through all of the values in its attributes. My first question is whether or not this is possible. If it is, will it be able to support a situation as follows: I define items and people as above then: state = State(items, people) for names, thing in state: print name + " is " + thing.color items[cheese] = ItemInstance3 for names, thing in state: print name + " weighs " + thing.weight While I feel like this would be usefull in the code I have, I don't know if it's either possible or the right approach. Everything I've read about user defined iterators has suggested that each instance of them is one use only.

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• Framework or design pattern for mailing all users of a webapp

  - by Todd Owen

  My app takes care of user registration (with the option to receive email announcements), and can easily handle the actual template-based rendering of email for a given user. JavaMail provides the mail transport layer. But how should I design the application layer between the business objects (e.g. User) and the mail transport? The straightforward approach would be a simple, synchronous loop: iterate through the users, queue the emails, and be done with it. "Queue" might mean sending them straight to the MTA (mail server), or to an in-memory queue to be consumed by another thread. However, I also plan to implement features like throttling the rate of emails, processing bounced emails (NDRs), and maintaining status across application restarts. My intuition is that a good design would decouple this from both the business layer and the mail transport layer as much as possible. I wondered if others had solved this problem before, but after much searching I haven't found any Java libraries which seem to fit this problem. Standalone mail apps such as James or list servers are too large in scope; packages like Spring's MailSender or Commons Email are too small in scope (being basically drop-in replacements for JavaMail). For other languages I haven't found anything appropriate either. I'm curious about how other developers have gone about adding bulk mailing to their applications.

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• Sweave can't see a vector if run from a function ?

  - by PaulHurleyuk

  I have a function that sets a vector to a string, copies a Sweave document with a new name and then runs that Sweave. Inside the Sweave document I want to use the vector I set in the function, but it doesn't seem to see it. (Edit: I changed this function to use tempdir(() as suggested by Dirk) I created a sweave file test_sweave.rnw; % \documentclass[a4paper]{article} \usepackage[OT1]{fontenc} \usepackage{Sweave} \begin{document} \title{Test Sweave Document} \author{gb02413} \maketitle <<>>= ls() Sys.time() print(paste("The chosen study was ",chstud,sep="")) @ \end{document} and I have this function; onOK <- function(){ chstud<-"test" message(paste("Chosen Study is ",chstud,sep="")) newfile<-paste(chstud,"_report",sep="") mypath<-paste(tempdir(),"\\",sep="") setwd(mypath) message(paste("Copying test_sweave.Rnw to ",paste(mypath,newfile,".Rnw",sep=""),sep="")) file.copy("c:\\local\\test_sweave.Rnw", paste(mypath,newfile,".Rnw",sep=""), overwrite=TRUE) Sweave(paste(mypath,newfile,".Rnw",sep="")) require(tools) texi2dvi(file = paste(mypath,newfile,".tex",sep=""), pdf = TRUE) } If I run the code from the function directly, the resulting file has this output for ls(); > ls() [1] "chstud" "mypath" "newfile" "onOK" However If I call onOK() I get this output; > ls() [1] "onOK" and the print(...chstud...)) function generates an error. I suspect this is an environment problem, but I assumed because the call to Sweave occurs within the onOK function, it would be in the same enviroment, and would see all the objects created within the function. How can I get the Sweave process to see the chstud vector ? Thanks Paul.

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