Emit介绍

官方msdn地址介绍：

https://docs.microsoft.com/zh-cn/dotnet/api/system.reflection.emit?view=netframework-4.8

https://docs.microsoft.com/zh-cn/dotnet/api/system.reflection.emit.assemblybuilder?view=netframework-4.8

定义

​ 在运行时构建一个程序集，然后创建类型

应用

​ 动态代理

流程

1.用AssemblyBuilder构建程序集

​ 需要先定义 assetblyName

//创建程序集名
AssemblyName aName = new AssemblyName("DynamicAssemblyExample");
//实例化AssemblyBuilder对象
AssemblyBuilder ab = 
AppDomain.CurrentDomain.DefineDynamicAssembly(
aName, 
AssemblyBuilderAccess.RunAndSave);

2.定义模块DefineDynamicModule创建ModuleBuilder

ModuleBuilder mb = 
            ab.DefineDynamicModule(aName.Name, aName.Name + ".dll");
 

3.创建动态类型TypeBuilder

TypeBuilder tb = mb.DefineType(
            "MyDynamicType", 
             TypeAttributes.Public);

4.定义方法MethodBuilder

MethodAttributes getSetAttr = MethodAttributes.Public | 
            MethodAttributes.SpecialName | MethodAttributes.HideBySig;

MethodBuilder mbNumberGetAccessor = tb.DefineMethod(
            "get_Number", // 方法名
            getSetAttr, //方法修饰符
            typeof(int), //返回值类型
            Type.EmptyTypes);//传入类型的数组

5实现方法

 ILGenerator numberSetIL = mbNumberSetAccessor.GetILGenerator();
        // Load the instance and then the numeric argument, then store the
        // argument in the field.
        numberSetIL.Emit(OpCodes.Ldarg_0);
        numberSetIL.Emit(OpCodes.Ldarg_1);
        numberSetIL.Emit(OpCodes.Stfld, fbNumber);
        numberSetIL.Emit(OpCodes.Ret);
      

6.创建类型并持久化到硬盘

根据自己的代码，改方法名和参数

Type type = typeBuilder.CreateType();
 
assemblyBuilder.Save(asmFileName);
 
object ob = Activator.CreateInstance(type);
 
for (int i = 1; i < 10; i++)
{
    Console.WriteLine(type.GetMethod("MyMethod").Invoke(ob, new object[] { i }));
}

示例类

public class MyDynamicType
{
    private int m_number;

    public MyDynamicType() : this(42) {}
    public MyDynamicType(int initNumber)
    {
        m_number = initNumber;
    }

    public int Number
    {
        get { return m_number; }
        set { m_number = value; }
    }

    public int MyMethod(int multiplier)
    {
        return m_number * multiplier;
    }
}