Question

I have a class called EventConsumer which defines an event EventConsumed and a method OnEventConsumed as follows:

public event EventHandler EventConsumed;  public virtual void OnEventConsumed(object sender, EventArgs e) {     if (EventConsumed != null)         EventConsumed(this, e); } 

I need to add attributes to the at OnEventConsumed runtime, so I’m generating a subclass using System.Reflection.Emit. What I want is the MSIL equivalent of this:

public override void OnEventConsumed(object sender, EventArgs e) {     base.OnEventConsumed(sender, e); } 

What I have so far is this:

...  MethodInfo baseMethod = typeof(EventConsumer).GetMethod('OnEventConsumed'); MethodBuilder methodBuilder = typeBuilder.DefineMethod('OnEventConsumed',                                                        baseMethod.Attributes,                                                        baseMethod.CallingConvention,                                                        typeof(void),                                                        new Type[] {typeof(object),                                                                    typeof(EventArgs)});  ILGenerator ilGenerator = methodBuilder.GetILGenerator();  // load the first two args onto the stack ilGenerator.Emit(OpCodes.Ldarg_1); ilGenerator.Emit(OpCodes.Ldarg_2);  // call the base method ilGenerator.EmitCall(OpCodes.Callvirt, baseMethod, new Type[0] );  // return ilGenerator.Emit(OpCodes.Ret);  ... 

I create the type, create an instance of the type, and call its OnEventConsumed function, and I get:

Common Language Runtime detected an invalid program. 

…which is not exactly helpful. What am I doing wrong? What’s the correct MSIL to call the base class’s event handler?

Answer 1

Here’s the IL from a sample app:

 .method public hidebysig virtual instance void OnEventConsumed(object sender, class [mscorlib]System.EventArgs e) cil managed     {         .maxstack 8         L_0000: nop          L_0001: ldarg.0          L_0002: ldarg.1          L_0003: ldarg.2          L_0004: call instance void SubclassSpike.BaseClass::OnEventConsumed(object, class [mscorlib]System.EventArgs)         L_0009: nop          L_000a: ret      } 

So I think you aren’t loading the instance because you aren’t doing a ldarg.0