IL Emit用于调用委托实例？

Question

基本上,我接受一个事件名称作为字符串,以获得EventInfo.然后,我发现使用反射的事件处理程序类型和事件参数类型,创建该类型的新委托(myEventHandler),并将其与事件挂钩.在myEventHandler调用时,我需要向下转换并将参数传递给处理程序.

我的代码如下.myEventHandler当调用'd'时,需要调用'handler' .我需要在那里放一些反射发射代码??? 有什么想法吗？

EventHandler handler = delegate(object sender, EventArgs eventArgs)
{
    //something will happen here                                
};

Type[] typeArgs = { typeof(object), derivedEventArgsType };

DynamicMethod myEventHandler = new DynamicMethod("", typeof(void), typeArgs);
var ilgen = myEventHandler.GetILGenerator();

//What should be the IL code here to 
//cast derviedEventArgs to EventArgs and
//invoke the 'handler' above??????
ilgen.Emit(OpCodes.Pop);
ilgen.Emit(OpCodes.Ret);



Delegate d = dynamic.CreateDelegate(derviedEventHandlerType);

//addMethod is the add MethodInfo for an Event
addMethod.Invoke(target, new object[] { d });

编辑:基于通过Reflector的观察.

反射器为手动编码的场景生成的代码是

.method public hidebysig instance void <Main>b__1(object sender, class ConsoleApplication2.MyEventArgs e) cil managed
{
    .maxstack 8
    L_0000: nop 
    L_0001: ldarg.0 
    L_0002: ldfld class [mscorlib]System.EventHandler ConsoleApplication2.Program/<>c__DisplayClass3::handler
    L_0007: ldarg.1 
    L_0008: ldarg.2 
    L_0009: callvirt instance void [mscorlib]System.EventHandler::Invoke(object, class [mscorlib]System.EventArgs)
    L_000e: nop 
    L_000f: ret 
}

这就是我在此基础上尝试的.

ilgen.Emit(OpCodes.Nop); 
ilgen.Emit(OpCodes.Ldarg_0);
ilgen.Emit(OpCodes.Ldfld,eh.GetType().GetField("handler"));
ilgen.Emit(OpCodes.Ldarg_1);
ilgen.Emit(OpCodes.Ldarg_2);
ilgen.EmitCall(OpCodes.Callvirt,eh.handler.Method,
               new Type[]{ typeof(object), typeof(EventArgs) });
ilgen.Emit(OpCodes.Nop);
ilgen.Emit(OpCodes.Ret);

但这会导致运行时错误:

'召集会议必须是varargs'

可能我错过了一些东西,需要更好地了解IL.

Answer 1

好的 - 这可能会有所帮助; 它生成IL以在委托类型之间切换,只要它们与标准模式匹配即可.它只在必要时添加一个castclass(所以如果你从a MouseEventArgs到a EventArgs它没有必要,但反过来它是).由于你显然正在使用反射,我没有使用泛型(这会使事情变得更难).

厚颜无耻的是,它不是使用捕获类,而是假装该方法属于我将捕获的数据,并将状态用作arg0.我无法判断这是否使它变得邪恶或聪明,所以我会选择"clevil".

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Threading;
using System.Windows.Forms;

class Program {
    static ParameterInfo[] VerifyStandardHandler(Type type) {
        if (type == null) throw new ArgumentNullException("type");
        if (!typeof(Delegate).IsAssignableFrom(type)) throw new InvalidOperationException();
        MethodInfo sig = type.GetMethod("Invoke");
        if (sig.ReturnType != typeof(void)) throw new InvalidOperationException();
        ParameterInfo[] args = sig.GetParameters();
        if (args.Length != 2 || args[0].ParameterType != typeof(object)) throw new InvalidOperationException();
        if (!typeof(EventArgs).IsAssignableFrom(args[1].ParameterType)) throw new InvalidOperationException();
        return args;
    }
    static int methodIndex;
    static Delegate Wrap(Delegate value, Type type) {
        ParameterInfo[] destArgs = VerifyStandardHandler(type);
        if (value == null) return null; // trivial
        if (value.GetType() == type) return value; // already OK
        ParameterInfo[] sourceArgs = VerifyStandardHandler(value.GetType());
        string name = "_wrap" + Interlocked.Increment(ref methodIndex);
        Type[] paramTypes = new Type[destArgs.Length + 1];
        paramTypes[0] = value.GetType();
        for (int i = 0; i < destArgs.Length; i++) {
            paramTypes[i + 1] = destArgs[i].ParameterType;
        }
        DynamicMethod dyn = new DynamicMethod(name, null, paramTypes);
        MethodInfo invoker = paramTypes[0].GetMethod("Invoke");
        ILGenerator il = dyn.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0);
        il.Emit(OpCodes.Ldarg_1);
        il.Emit(OpCodes.Ldarg_2);
        if (!sourceArgs[1].ParameterType.IsAssignableFrom(destArgs[1].ParameterType)) {
            il.Emit(OpCodes.Castclass, sourceArgs[1].ParameterType);
        }
        il.Emit(OpCodes.Call, invoker);
        il.Emit(OpCodes.Ret);
        return dyn.CreateDelegate(type, value);
    }
    static void Main() {
        EventHandler handler = delegate(object sender, EventArgs eventArgs) {
            Console.WriteLine(eventArgs.GetType().Name);
        };
        MouseEventHandler wrapper = (MouseEventHandler)Wrap(handler, typeof(MouseEventHandler));
        MouseEventArgs ma = new MouseEventArgs(MouseButtons.Left, 1, 1, 1, 1);
        wrapper(new object(), ma);

        EventHandler backAgain = (EventHandler)Wrap(wrapper, typeof(EventHandler));
        backAgain(new object(), ma);
    }
}

显然你仍然需要使用常规方法(Delegate.CreateDelegate等)生成事件的委托,但是你可以将它包装成一个EventHandler或相反.

Answer 2

事实证明,我的事情过于复杂!巴里凯利有正确的想法:

static T CastDelegate<T>(Delegate src)
    where T : class
{
    return (T)(object)Delegate.CreateDelegate(
        typeof(T),
        src.Target,
        src.Method,
        true); // throw on fail
}

这适用于我的测试用例.