秒懂C#通过Emit动态生成代码

 // specify a new assembly name
var assemblyName = new AssemblyName("Kitty");

 // create assembly builder
 var assemblyBuilder = AppDomain.CurrentDomain
   .DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);

 // create module builder
 var moduleBuilder = assemblyBuilder.DefineDynamicModule("KittyModule", "Kitty.exe");

模块即是代码的集合，一个程序集中可以有多个模块。并且理论上讲，每个模块可以使用不同的编程语言实现，例如C#/VB。
构造一个类型构造器，

 // create type builder for a class
var typeBuilder = moduleBuilder.DefineType("HelloKittyClass", TypeAttributes.Public);

// create method builder
var methodBuilder = typeBuilder.DefineMethod(
  "SayHelloMethod",
  MethodAttributes.Public | MethodAttributes.Static,
  null,
  null);

// then get the method il generator
var il = methodBuilder.GetILGenerator();

// then create the method function
il.Emit(OpCodes.Ldstr, "Hello, Kitty!");
il.Emit(OpCodes.Call,
  typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }));
il.Emit(OpCodes.Call, typeof(Console).GetMethod("ReadLine"));
il.Emit(OpCodes.Pop); // we just read something here, throw it.
il.Emit(OpCodes.Ret);

// then create the whole class type
 var helloKittyClassType = typeBuilder.CreateType();

如果当前程序集是可运行的，则设置一个程序入口，

 // set entry point for this assembly
 assemblyBuilder.SetEntryPoint(helloKittyClassType.GetMethod("SayHelloMethod"));

将动态生成的程序集保存成磁盘文件，

 // save assembly
 assemblyBuilder.Save("Kitty.exe");

此时，通过反编译工具，将Kitty.exe反编译成代码，

using System;

public class HelloKittyClass
{
  public static void SayHelloMethod()
  {
    Console.WriteLine("Hello, Kitty!");
    Console.ReadLine();
  }
}

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

namespace EmitIntroduction
{
  class Program
  {
    static void Main(string[] args)
    {
      // specify a new assembly name
      var assemblyName = new AssemblyName("Kitty");

      // create assembly builder
      var assemblyBuilder = AppDomain.CurrentDomain
        .DefineDynamicAssembly(assemblyName,
          AssemblyBuilderAccess.RunAndSave);

      // create module builder
      var moduleBuilder =
        assemblyBuilder.DefineDynamicModule(
          "KittyModule", "Kitty.exe");

      // create type builder for a class
      var typeBuilder =
        moduleBuilder.DefineType(
          "HelloKittyClass", TypeAttributes.Public);

      // create method builder
      var methodBuilder = typeBuilder.DefineMethod(
        "SayHelloMethod",
        MethodAttributes.Public | MethodAttributes.Static,
        null,
        null);

      // then get the method il generator
      var il = methodBuilder.GetILGenerator();

      // then create the method function
      il.Emit(OpCodes.Ldstr, "Hello, Kitty!");
      il.Emit(OpCodes.Call,
        typeof(Console).GetMethod(
        "WriteLine", new Type[] { typeof(string) }));
      il.Emit(OpCodes.Call,
        typeof(Console).GetMethod("ReadLine"));
      il.Emit(OpCodes.Pop); // we just read something here, throw it.
      il.Emit(OpCodes.Ret);

      // then create the whole class type
      var helloKittyClassType = typeBuilder.CreateType();

      // set entry point for this assembly
      assemblyBuilder.SetEntryPoint(
        helloKittyClassType.GetMethod("SayHelloMethod"));

      // save assembly
      assemblyBuilder.Save("Kitty.exe");

      Console.WriteLine(
        "Hi, Dennis, a Kitty assembly has been generated for you.");
      Console.ReadLine();
    }
  }
}