Constructing Objects and Calling Methods Using IL

Question

I wrote following program in order to understand object construction and method call in IL Unfortunately it doesn’t print

How are you doing

on the console.

Do you have any idea?

Output of peverify is also given below.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection.Emit;
using System.Reflection;
using System.IO;

namespace Research
{
    public class Program
    {
        public static void Main(string[] args)
        {
            AssemblyName name = 
                new AssemblyName(Path.GetFileNameWithoutExtension("Hello"));
            AssemblyBuilder asmb = 
                System.AppDomain.CurrentDomain.DefineDynamicAssembly(name, 
                                                    AssemblyBuilderAccess.Save);
            ModuleBuilder modb = asmb.DefineDynamicModule("Hello");
            TypeBuilder typeBuilder = modb.DefineType("Bar");
            MethodBuilder methb = 
                typeBuilder.DefineMethod("Me", MethodAttributes.Static, 
                                            typeof(void), System.Type.EmptyTypes);
            ILGenerator gen = methb.GetILGenerator();

            ConstructorInfo cil = typeof(Research.Dog).GetConstructor(new Type[] { });
            gen.Emit(OpCodes.Newobj, cil);
            gen.Emit(OpCodes.Call, typeof(Research.Dog).GetMethod("Bark"));
            gen.Emit(OpCodes.Ret);
        }
    }
    public class Dog
    {
        public void Bark()
        {
            Console.WriteLine("How are you doing");
        }
    }
}

C:\temp\Research\Research\bin\Release>peverify Research.exe

Microsoft (R) .NET Framework PE Verifier. Version 4.0.30319.1 Copyright (c) Microsoft Corporation. All rights reserved.

All Classes and Methods in Research.exe Verified.

C:\temp\Research\Research\bin\Release>

svick svick · Accepted Answer · 2011-06-05T13:45:25

You create a dynamic assembly and then do nothing with it. Why should that print anything? Also, peverify won't help you in any way here, because you're not verifying the assembly you generated, you're verifying just the assembly that's generating it.

You also don't call typeBuilder.CreateType(), which is necessary and your assembly isn't set to be able to run.

If you use AssemblyBuilderAccess.RunAndSave and add the following code at the end of the method, it will work (at least it works for me):

var barType = typeBuilder.CreateType();
var meMethod = barType.GetMethod("Me", BindingFlags.Static | BindingFlags.NonPublic);
meMethod.Invoke(null, null);

Constructing Objects and Calling Methods Using IL

1 Answers