// 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);
}
}
}
