// Addes a new method to the class that can unsubscribe a weak event handler from the event delegate // E.g. #pragma warning disable S125 // Sections of code should not be "commented out" // [CompilerGenerated] // private void <event name>_Weak_Unsubscribe(EventHandler< eventargsType > weh) // { // this.EventDelegate = (<event type>) Delegate.Remove(this.EventDelegate, (<event type>)weh); // } #pragma warning restore S125 // Sections of code should not be "commented out" // This is used as a call back by the weak event handler to clean up when the target is garbage collected. public MethodDefinition AddUnsubscribeMethod() { // private void <event name>_Weak_Unsubscribe(EventHandler< eventargsType > weh) string unsubscribeMethodName = string.Format(CultureInfo.InvariantCulture, "<{0}>_Weak_Unsubscribe", _eventDelegate.Name); MethodDefinition unsubscribe = new MethodDefinition(unsubscribeMethodName, GetUnsubscribeMethodAttributes(), _eventDelegate.Module.TypeSystem.Void); unsubscribe.Parameters.Add(new ParameterDefinition(_closedGenericEventHandler)); // [CompilerGenerated] unsubscribe.CustomAttributes.Add(_moduleimporter.CompilerGeneratedAttribute); _eventDelegate.DeclaringType.Methods.Add(unsubscribe); var rootEmitter = new EmptyEmitter(unsubscribe, _moduleimporter); var weakHandler = rootEmitter.LoadMethodFirstArg(); if (!_isGenericHandler) { weakHandler = rootEmitter.DelegateConvert(weakHandler, _eventDelegate.FieldType); } var removeFromFieldDelegate = rootEmitter.CallDelegateRemove(rootEmitter.LoadField(_eventDelegate), weakHandler); var compatibleHandler = removeFromFieldDelegate; if (!_isGenericHandler) { compatibleHandler = rootEmitter.DelegateConvert(removeFromFieldDelegate, _eventDelegate.FieldType); } var instructions = rootEmitter.StoreField(compatibleHandler, _eventDelegate).Return(); unsubscribe.InsertInstructions(instructions, 0); return unsubscribe; }
private static void ProcessAddMethod(MethodDefinition addMethod, WeakEventWeaver weakEventWeaver) { var weakEventHandler = weakEventWeaver.CreateEventHandlerVariable(addMethod); var makeWeak = weakEventWeaver.GenerateMakeWeakIl(addMethod, weakEventWeaver.AddUnsubscribeMethod(), weakEventHandler); int oldCodeIndex = addMethod.InsertInstructions(makeWeak, 0); // Now replace any further use of the method parameter (Ldarg_1, or Ldarg_0 if static) with the weak event handler var instructionToReplace = GetMethodLoadFirstArgumentCode(addMethod); var instructions = addMethod.Body.Instructions; for (int i = oldCodeIndex; i < instructions.Count; i++) { if (instructions[i].OpCode.Code.Equals(instructionToReplace)) { instructions[i] = Instruction.Create(OpCodes.Ldloc, weakEventHandler); } } }