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• Why delegate types are derived from MulticastDelegate class why not it directly derive from Delegate class?

  - by Vijay

  I have a very basic question regarding delegate types. I compared the memebers of Delegate and MulticastDelegate classes in object browser and I couldn't find any new additional member present in MulticastDelegate. I also noticed that the Delegate class has GetInvocationList virtual method. So I assume that the Delegate class should have the capability to hold references to multiple methods. If my assumption is correct I wonder why not custom delegate types directly derive from the Delegate class instead of MulticastDelegate class. Not sure what I am missing here. Please help me understand the difference.

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• Delegates in .NET: how are they constructed ?

  - by Saulius

  While inspecting delegates in C# and .NET in general, I noticed some interesting facts: Creating a delegate in C# creates a class derived from MulticastDelegate with a constructor: .method public hidebysig specialname rtspecialname instance void .ctor(object 'object', native int 'method') runtime managed { } Meaning that it expects the instance and a pointer to the method. Yet the syntax of constructing a delegate in C# suggests that it has a constructor new MyDelegate(int () target) where I can recognise int () as a function instance (int *target() would be a function pointer in C++). So obviously the C# compiler picks out the correct method from the method group defined by the function name and constructs the delegate. So the first question would be, where does the C# compiler (or Visual Studio, to be precise) pick this constructor signature from ? I did not notice any special attributes or something that would make a distinction. Is this some sort of compiler/visualstudio magic ? If not, is the T (args) target construction valid in C# ? I did not manage to get anything with it to compile, e.g.: int () target = MyMethod; is invalid, so is doing anything with MyMetod, e.g. calling .ToString() on it (well this does make some sense, since that is technically a method group, but I imagine it should be possible to explicitly pick out a method by casting, e.g. (int())MyFunction. So is all of this purely compiler magic ? Looking at the construction through reflector reveals yet another syntax: Func CS$1$0000 = new Func(null, (IntPtr) Foo); This is consistent with the disassembled constructor signature, yet this does not compile! One final interesting note is that the classes Delegate and MulticastDelegate have yet another sets of constructors: .method family hidebysig specialname rtspecialname instance void .ctor(class System.Type target, string 'method') cil managed Where does the transition from an instance and method pointer to a type and a string method name occur ? Can this be explained by the runtime managed keywords in the custom delegate constructor signature, i.e. does the runtime do it's job here ?

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• Banshee crashes consistently - is there a fix?

  - by user36334

  Since updating to ubuntu 11.10 I've had trouble with banshee. In particular when I run it I find that it crashes within an hour without fail. I get the following Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object at Mono.Zeroconf.Providers.AvahiDBus.BrowseService.DisposeResolver () [0x00000] in <filename unknown>:0 at Mono.Zeroconf.Providers.AvahiDBus.BrowseService.Dispose () [0x00000] in <filename unknown>:0 at Mono.Zeroconf.Providers.AvahiDBus.ServiceBrowser.OnItemRemove (Int32 interface, Protocol protocol, System.String name, System.String type, System.String domain, LookupResultFlags flags) [0x00000] in <filename unknown>:0 at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0 --- End of inner exception stack trace --- at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0 at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0 at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x00000] in <filename unknown>:0 at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00000] in <filename unknown>:0 at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] in <filename unknown>:0 at NDesk.DBus.Connection.HandleSignal (NDesk.DBus.Message msg) [0x00000] in <filename unknown>:0 at NDesk.DBus.Connection.DispatchSignals () [0x00000] in <filename unknown>:0 at NDesk.DBus.Connection.Iterate () [0x00000] in <filename unknown>:0 at Mono.Zeroconf.Providers.AvahiDBus.DBusManager.IterateThread (System.Object o) [0x00000] in <filename unknown>:0 Does anyone else also have this problem?

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• Cast to delegate type fails in JScript.NET

  - by dnewcome

  I am trying to do async IO using BeginRead() in JScript.NET, but I can't get the callback function to work correctly. Here is the code: function readFileAsync() { var fs : FileStream = new FileStream( 'test.txt', FileMode.Open, FileAccess.Read ); var result : IAsyncResult = fs.BeginRead( new byte[8], 0, 8, readFileCallback ), fs ); Thread.Sleep( Timeout.Infinite ); } var readFileCallback = function( result : IAsyncResult ) : void { print( 'ListenerCallback():' ); } The exception is a cast failure: Unhandled Exception: System.InvalidCastException: Unable to cast object of type 'Microsoft.JScript.Closure' to type 'System.AsyncCallback'. at JScript 0.readFileAsync(Object this, VsaEngine vsa Engine) at JScript 0.Global Code() at JScript Main.Main(String[] ) I have tried doing an explicit cast both to AsyncCallback and to the base MulticastDelegate and Delegate types to no avail. Delegates are supposed to be created automatically, obviating the need for creating a new AsyncCallback explicitly, eg: BeginRead( ... new AsyncDelegate( readFileCallback), object ); And in fact if you try to create the delegate explicitly the compiler issues an error. I must be missing something here.

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• Why won't this hit test fire a second time? wpf

  - by csciguy

  All, I have a main window that contains two custom objects (AnimatedCharacter). These objects are nothing but images. These images might contain transparent portions. One of these objects slightly overlaps the other object. There is a listener attached to the main window and is as follows. private void Window_MouseLeftButtonUp_1(object sender, MouseButtonEventArgs e) { Point pt = e.GetPosition((UIElement)sender); //store off the mouse pt hitPointMouse = pt; //clear the result list hitResultsSubList.Clear(); EllipseGeometry m_egHitArea = new EllipseGeometry(pt, 1, 1); VisualTreeHelper.HitTest(sender as Visual, HitTestFilterFuncNew, new HitTestResultCallback(HitTestCallback), new GeometryHitTestParameters(m_egHitArea)); //Check all sub items you have now hit if (hitResultsSubList.Count > 0) { CheckSubHitItems(hitResultsSubList); } } The idea is to filter out only a select group of items (called AnimatedCharacters). The hittest and filters are as follows public HitTestResultBehavior HitTestCallback(HitTestResult htrResult) { IntersectionDetail idDetail = ((GeometryHitTestResult)htrResult).IntersectionDetail; switch (idDetail) { case IntersectionDetail.FullyContains: return HitTestResultBehavior.Continue; case IntersectionDetail.Intersects: return HitTestResultBehavior.Continue; case IntersectionDetail.FullyInside: return HitTestResultBehavior.Continue; default: return HitTestResultBehavior.Stop; } } public HitTestFilterBehavior HitTestFilterFuncNew(DependencyObject potentialHitTestTarget) { if (potentialHitTestTarget.GetType() == typeof(AnimatedCharacter)) { hitResultsSubList.Add(potentialHitTestTarget as AnimatedCharacter); } return HitTestFilterBehavior.Continue; } This returns me back a list (called hitResultsSubList) that I attempt to then process further. I want to take everything in the hitResultsSubList and run a hit test on it again. This time, the hit test will be checking alpha levels on the particular animatedCharacter object. private void CheckSubHitItems(List<DependencyObject> hitResultsSub) { for(int i = 0; i<hitResultsSub.Count; i++) { hitResultsList.Clear(); AnimatedCharacter ac = hitResultsSub[i] as AnimatedCharacter; try { //DEBUGGER SKIPS THIS NEXT LINE EVERY SINGLE TIME. VisualTreeHelper.HitTest(ac, null, new HitTestResultCallback(hitCallBack), new PointHitTestParameters(hitPointMouse)); } catch (Exception e) { System.Diagnostics.Debug.WriteLine(e.StackTrace); } if (hitResultsList.Count > 0) { //do something here } } } Here is my problem now. The hit test in the second function (CheckSubHitItems) never gets called. There are definitely items (DependencyObjects of the type AnimatedCharacter) in the hitResultSub, but no matter what, the second hit test will not fire. I can walk the for loop fine, but when that line is hit, I get the following console statement. Step into: Stepping over non-user code 'System.MulticastDelegate.CtorClosed' No exceptions are thrown. Any help is appreciated.

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