mardi 26 mai 2020

C# - Reflection.Emit : Return result of called method

In a DynamicMethod I try to call a method that wants an array of objects to return the length of the given array. Currently, my method which should be called from the DynamicMethod looks like the following:

public static int Test(Object[] args)
{
    Console.WriteLine(args.Length);
    return args.Length;
}

The creation process of the DynamicMethod looks like the following:

(The creation of the Object array is adopted from the following SO answer)

public static DynamicMethod GetDM()
{ 
    var returnType = typeof(int);
    var paramTypes = new Type[]{typeof(string), typeof(bool)};

    var method = new DynamicMethod(
        "",
        returnType,
        paramTypes,
        false
    );
    var il = method.GetILGenerator();

    // Save parameters in an object array
    il.Emit(OpCodes.Ldc_I4_S, paramTypes.Length);
    il.Emit(OpCodes.Newarr, typeof(Object));
    il.Emit(OpCodes.Dup);

    for (int i = 0; i < paramTypes.Length; i++)
    {
        Type type = paramTypes[i];

        il.Emit(OpCodes.Ldc_I4, i);
        il.Emit(OpCodes.Ldarg, i);
        if (type.IsValueType) { il.Emit(OpCodes.Box, type); }
        il.Emit(OpCodes.Stelem_Ref);
        il.Emit(OpCodes.Dup);
    }

    // Call method and get the length of the array
    // How do I return the result of the called method?
    var callMethod = typeof(Program).GetMethod("Test", (BindingFlags)(-1));
    il.Emit(OpCodes.Call, callMethod);

    il.Emit(OpCodes.Ret);

    return method;
}

With the following method I check the functionality:

public static void Main(string[] args)
{
    var method = GetDM();
    var result = method.Invoke(null, new Object[]{"Test 1234", true});
    Console.WriteLine(result); // Should be 2
}

When I run the main method I get the System.Reflection.TargetInvocationException. Can someone help me out how to return the value which was returned by the called method? Here is a link to a dotnetfiddle to see my problem in action.





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