如何使用反射在 C# 中发出和调用事件？

Question

我正在尝试在运行时使用反射创建一个事件并尝试在操作之前调用它。类似 INotifyPropertyChanged 的东西。但我不能调用我的事件。我希望它调用订阅方法，在本例中为 Boss1.HeardIt() 并将 "I Heard you buddy" 打印到屏幕。我做错了什么，我该怎么做？

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using System.Text;
using System.Threading.Tasks;

namespace WhosebugSoru
{
    public delegate void SomeththingHappenedEventHandler();
    public interface Iperson
    {

        void Work(string message);

        event SomeththingHappenedEventHandler SomeththingHappened;
    }
    public class person : Iperson
    {
        public event SomeththingHappenedEventHandler SomeththingHappened;

        public void Work(string thework)
        {
            Console.WriteLine("Working on: {0}", thework);
        }
    }

    class Boss
    {
        public void HeardIt()
        {
            Console.WriteLine("I Heard you buddy");
        }
    }
    class Program
    {
        static Type CreateDynamicProxyType()
        {
            var assemblyName = new AssemblyName("MyProxies");
            var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(
                   assemblyName,
                   AssemblyBuilderAccess.Run);
            var modBuilder = assemblyBuilder.DefineDynamicModule("MyProxies");

            // public class person
            // {
            var typeBuilder = modBuilder.DefineType(
                "mypersonproxy",
                TypeAttributes.Public | TypeAttributes.Class,
                typeof(object),
                new[] { typeof(Iperson) });

            //      private person _realObject;
            var fieldBuilder = typeBuilder.DefineField(
                "_realObject",
                typeof(person),
                FieldAttributes.Private);
            //event
            var field = typeBuilder.DefineField("SomeththingHappened", typeof(SomeththingHappenedEventHandler), FieldAttributes.Private);
            var eventInfo = typeBuilder.DefineEvent("SomeththingHappened", EventAttributes.None, typeof(SomeththingHappenedEventHandler));

            //add
            var addMethod = typeBuilder.DefineMethod("add_SomeththingHappened",
        MethodAttributes.Public | MethodAttributes.Virtual | MethodAttributes.SpecialName | MethodAttributes.Final | MethodAttributes.HideBySig | MethodAttributes.NewSlot,
        CallingConventions.Standard | CallingConventions.HasThis,
        typeof(void),
        new[] { typeof(SomeththingHappenedEventHandler)});
            var generator = addMethod.GetILGenerator();
            var combine = typeof(Delegate).GetMethod("Combine", new[] { typeof(Delegate), typeof(Delegate) });
            generator.Emit(OpCodes.Ldarg_0);
            generator.Emit(OpCodes.Ldarg_0);
            generator.Emit(OpCodes.Ldfld, field);
            generator.Emit(OpCodes.Ldarg_1);
            generator.Emit(OpCodes.Call, combine);
            generator.Emit(OpCodes.Castclass, typeof(SomeththingHappenedEventHandler));
            generator.Emit(OpCodes.Stfld, field);
            generator.Emit(OpCodes.Ret);
            eventInfo.SetAddOnMethod(addMethod);

            //remove
            var removeMethod = typeBuilder.DefineMethod("remove_SomeththingHappened",
        MethodAttributes.Public | MethodAttributes.Virtual | MethodAttributes.SpecialName | MethodAttributes.Final | MethodAttributes.HideBySig | MethodAttributes.NewSlot,
        CallingConventions.Standard | CallingConventions.HasThis,
        typeof(void),
        new[] { typeof(SomeththingHappenedEventHandler) });
        var remove = typeof(Delegate).GetMethod("Remove", new[] { typeof(Delegate), typeof(Delegate) });
            var removator = removeMethod.GetILGenerator();
            removator.Emit(OpCodes.Ldarg_0);
            removator.Emit(OpCodes.Ldarg_0);
            removator.Emit(OpCodes.Ldfld, field);
            removator.Emit(OpCodes.Ldarg_1);
            removator.Emit(OpCodes.Call, remove);
            removator.Emit(OpCodes.Castclass, typeof(SomeththingHappenedEventHandler));
            removator.Emit(OpCodes.Stfld, field);
            removator.Emit(OpCodes.Ret);
            eventInfo.SetRemoveOnMethod(removeMethod);

            //      public mypersonproxy(person arg1)
            //      {
            var constructorBuilder = typeBuilder.DefineConstructor(
                MethodAttributes.Public,
                CallingConventions.HasThis,
                new[] { typeof(person) });
            var contructorIl = constructorBuilder.GetILGenerator();
            contructorIl.Emit(OpCodes.Ldarg_0);
            contructorIl.Emit(OpCodes.Ldarg_1);
            contructorIl.Emit(OpCodes.Stfld, fieldBuilder);
            contructorIl.Emit(OpCodes.Ret);
            //      }

            //      public void Work(string arg1)
            //      {
            var methodBuilder = typeBuilder.DefineMethod("Work",
                MethodAttributes.Public | MethodAttributes.Virtual,
                typeof(void),
                new[] { typeof(string) });
            typeBuilder.DefineMethodOverride(methodBuilder,
                typeof(Iperson).GetMethod("Work"));
            var tweetIl = methodBuilder.GetILGenerator();

            //          Console.WriteLine("Hello before!");
            tweetIl.Emit(OpCodes.Ldstr, "Hello before!");
            tweetIl.Emit(OpCodes.Call, typeof(Console)
                .GetMethod("WriteLine", new[] { typeof(string) }));

            //raise probably something wrong here
            var eventmethodBuilder = typeBuilder.DefineMethod("OnSomeththingHappened",
        MethodAttributes.Family | MethodAttributes.Virtual | MethodAttributes.HideBySig | MethodAttributes.NewSlot,
        typeof(void),
        new[] { typeof(string) });
            var methodgenerator = eventmethodBuilder.GetILGenerator();

            var returnLabel = methodgenerator.DefineLabel();

            var eventArgsCtor = typeof(PropertyChangedEventArgs).GetConstructor(new[] { typeof(string) });

            methodgenerator.DeclareLocal(typeof(PropertyChangedEventHandler));

            methodgenerator.Emit(OpCodes.Ldarg_0);
            methodgenerator.Emit(OpCodes.Ldfld, field); 
            methodgenerator.Emit(OpCodes.Stloc_0);
            methodgenerator.Emit(OpCodes.Ldloc_0);
            methodgenerator.Emit(OpCodes.Brfalse, returnLabel);
            methodgenerator.Emit(OpCodes.Ldloc_0);
            methodgenerator.Emit(OpCodes.Ldarg_0);
            methodgenerator.Emit(OpCodes.Ldarg_1);

            methodgenerator.Emit(OpCodes.Newobj, eventArgsCtor);
            methodgenerator.Emit(OpCodes.Callvirt, typeof(PropertyChangedEventHandler).GetMethod("Invoke"));
            methodgenerator.MarkLabel(returnLabel);
            methodgenerator.Emit(OpCodes.Ret);

            eventInfo.SetRaiseMethod(eventmethodBuilder);


            //          _realObject.Work(arg1);
            tweetIl.Emit(OpCodes.Ldarg_0);
            tweetIl.Emit(OpCodes.Ldfld, fieldBuilder);
            tweetIl.Emit(OpCodes.Ldarg_1);
            tweetIl.Emit(OpCodes.Call,
                fieldBuilder.FieldType.GetMethod("Work"));

            //          Console.WriteLine("Hello after!");
            tweetIl.Emit(OpCodes.Ldstr, "Hello after!");
            tweetIl.Emit(OpCodes.Call, typeof(Console)
                .GetMethod("WriteLine", new[] { typeof(string) }));
            tweetIl.Emit(OpCodes.Ret);
            //      }
            // }


            return typeBuilder.CreateType();
        }

        static void Main(string[] args)
        {
            Boss boss1 = new Boss();

            var type = CreateDynamicProxyType();

            var dynamicProxy = (Iperson)Activator.CreateInstance(
                type, new object[] { new person() });

            dynamicProxy.SomeththingHappened += boss1.HeardIt;

            dynamicProxy.Work("fill the excel documents");
        }
    }
}

Answer 1

在代理上生成 Work 方法时，您似乎忘记为调用 SomeththingHappened.Invoke() 发出 IL，您必须添加

tweetIl.Emit(OpCodes.Ldarg_0);
tweetIl.Emit(OpCodes.Ldfld, field);
tweetIl.Emit(OpCodes.Callvirt, typeof(SomeththingHappenedEventHandler).GetMethod("Invoke"));

after tweetIl.Emit(OpCodes.Call, fieldBuilder.FieldType.GetMethod("Work"));（假设您希望在调用 _realObject.Work(...) 之后引发事件）。

如果您想添加空检查以确保 SomeththingHappened 不是 null，您可以改用此版本

Label retLabel = tweetIl.DefineLabel();
tweetIl.Emit(OpCodes.Ldarg_0);
tweetIl.Emit(OpCodes.Ldfld, field);
tweetIl.Emit(OpCodes.Brfalse_S, retLabel);
tweetIl.Emit(OpCodes.Ldarg_0);
tweetIl.Emit(OpCodes.Ldfld, field);
tweetIl.Emit(OpCodes.Callvirt, typeof(SomeththingHappenedEventHandler).GetMethod("Invoke"));

// some other code if you want

tweetIl.MarkLabel(retLabel); //if not null ends here
tweetIl.Emit(OpCodes.Ret);

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