Emit with a human face-优快云博客

本文详细介绍了System.Reflection.Emit命名空间在.NET框架中的动态编程使用方法，通过示例展示了如何创建动态类型、方法和MSIL代码，以及如何将其编译并保存到磁盘。

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Introduction

The System.Reflection.Emit namespace provides classes to create dynamic assemblies at runtime. It allows compilers and tools to emit MSIL, execute it and store it to a disk. Although Emit is a powerful tool, it is also extremely hard to use.

Let us take a look at the following example, which demonstrates the "normal" way of Emit programming:

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Threading;

namespace EmitDemo
{
    public interface IHello
    {
        void SayHello(string toWhom);
    }

    class Program
    {
        static void Main(string[] args)
        {
            AssemblyName asmName = new AssemblyName();

            asmName.Name = "HelloWorld";

            AssemblyBuilder asmBuilder =
                Thread.GetDomain().DefineDynamicAssembly
            (asmName, AssemblyBuilderAccess.RunAndSave);

            ModuleBuilder modBuilder  = asmBuilder.DefineDynamicModule
                            ("HelloWorld");

            TypeBuilder   typeBuilder = modBuilder.DefineType(
                                    "Hello",
                                    TypeAttributes.Public,
                                    typeof(object),
                                    new Type[] { typeof(IHello) });

            MethodBuilder methodBuilder = typeBuilder.DefineMethod("SayHello",
                         MethodAttributes.Private | MethodAttributes.Virtual,
                         typeof(void),
                         new Type[] { typeof(string) });

            typeBuilder.DefineMethodOverride(methodBuilder, 
                    typeof(IHello).GetMethod("SayHello"));

            ILGenerator il = methodBuilder.GetILGenerator();

            // string.Format("Hello, {0} World!", toWhom)
            //
            il.Emit(OpCodes.Ldstr, "Hello, {0} World!");
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Call, typeof(string).GetMethod
        ("Format", new Type[] { typeof(string), typeof(object) }));

            // Console.WriteLine("Hello, World!");
            //
            il.Emit(OpCodes.Call, typeof(Console).GetMethod
            ("WriteLine", new Type[] { typeof(string) }));
            il.Emit(OpCodes.Ret);

            Type   type  = typeBuilder.CreateType();

            IHello hello = (IHello)Activator.CreateInstance(type);

            hello.SayHello("Emit");
        }
    }
}

using System;

using BLToolkit.Reflection;
using BLToolkit.Reflection.Emit;

namespace EmitHelperDemo
{
    public interface IHello
    {
        void SayHello(string toWhom);
    }

    class Program
    {
        static void Main(string[] args)
        {
            EmitHelper emit = new AssemblyBuilderHelper("HelloWorld.dll")
                .DefineType  ("Hello", typeof(object), typeof(IHello))
                .DefineMethod(typeof(IHello).GetMethod("SayHello"))
                .Emitter;

            emit
                // string.Format("Hello, {0} World!", toWhom)
                //
                .ldstr   ("Hello, {0} World!")
                .ldarg_1
                .call    (typeof(string), "Format", typeof(string), 
                                            typeof(object))

                // Console.WriteLine("Hello, World!");
                //
                .call    (typeof(Console), "WriteLine", typeof(string))
                .ret()
                ;

            Type   type  = emit.Method.Type.Create();

            IHello hello = (IHello)TypeAccessor.CreateInstance(type);

            hello.SayHello("C#");
        }
    }
}