使用反射发出泛型方法在Invoke处引发异常

Question

我正在尝试这个使用Reflection.Emit创建泛型方法的简单示例，但它在调用Invoke时导致异常，我找不到问题。

public class Program
{
    public static void Main(string[] args)
    {
        AppDomain appDomain = AppDomain.CurrentDomain;
        AssemblyName name = new AssemblyName("MyAssembly") { Version = new Version("1.0.0.0") };
        AssemblyBuilder ab = appDomain.DefineDynamicAssembly(name, AssemblyBuilderAccess.RunAndSave);
        ModuleBuilder mb = ab.DefineDynamicModule("MyModule", "MyAssembly.dll");
        TypeBuilder tb = mb.DefineType("Widget", TypeAttributes.Public);
        // Define a method builder
        MethodBuilder methodBuilder = tb.DefineMethod("MyGenericMethod", MethodAttributes.Public | MethodAttributes.Static);
        // Get generic type parameter builders 
        GenericTypeParameterBuilder[] genericParams =
            methodBuilder.DefineGenericParameters("TKey", "TValue");
        methodBuilder.SetSignature(typeof(int), null, null,
            genericParams,
            null, null);
        methodBuilder.DefineParameter(1, ParameterAttributes.None, "key");
        methodBuilder.DefineParameter(2, ParameterAttributes.None, "val");
        ILGenerator gen = methodBuilder.GetILGenerator();
        MethodInfo writeLineStr = typeof(Console).GetMethod("WriteLine", new[] { typeof(object) });
        gen.Emit(OpCodes.Ldarg_0);
        gen.Emit(OpCodes.Box, genericParams[0]);
        gen.Emit(OpCodes.Call, writeLineStr);
        gen.Emit(OpCodes.Ldarg_1);
        gen.Emit(OpCodes.Box, genericParams[1]);
        gen.Emit(OpCodes.Call, writeLineStr);
        gen.Emit(OpCodes.Ret);
        Type t = tb.CreateType();
        MethodInfo genMeth = t.GetMethod("MyGenericMethod").MakeGenericMethod(typeof(string), typeof(int));
        genMeth.Invoke(null, new object[] { "NumberKey", 100 });
    }
}

调用genMeth.Invoke时，会引发以下异常

Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the t
arget of an invocation. ---> System.InvalidProgramException: Common Language Runtime detected an inv
alid program.
   at Widget.MyGenericMethod[TKey,TValue](TKey key, TValue val)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Bool
ean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Obje
ct[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder,
 Object[] parameters, CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
   at ReflectionEmitDemo14.Program.Main(String[] args) in d:ProjectsReflectionEmitDemoReflectionE
mitDemo14Program.cs:line 50

Answer 1

您的方法是静态的，有两个参数：参数0和参数1。但在生成的IL代码中，您正在访问一个不存在的参数2。

另一个问题是，您试图将Int32值传递给一个需要String引用的方法。框住这两个参数，并将它们传递给接受Object引用的WriteLine重载。

您还声明了返回Int32的方法，但在返回之前没有在堆栈中放入任何内容。

尝试用C#编写方法，然后看看C#编译器发出的IL（例如，使用ILspy）。它应该是这样的：

ldarg.0
box !TKey
call void [mscorlib]System.Console::WriteLine(object)
ldarg.1
box !TValue
call void [mscorlib]System.Console::WriteLine(object)
ldc.i4.s 42
ret