C#中委托的+=和-=深入研究

2020-01-24 02:12:28

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来源：转载

供稿：网友

写在前面

为什么会突然想说说委托?原因吗，起于一个同事的想法，昨天下班的路上一直在想这个问题，如果给委托注册多个方法，会不会都执行呢？为了一探究性，就弄了个demo研究下。

大家都知道委托都继承自System.MulticastDelegate,而System.MulticastDelegate又继承自System.Delegate，可以通过+=为委托注册多个方法。那么他们是否都执行了呢？执行的结果又是怎样的呢？有返回值和没返回值的是否结果是否一样？那就试着说说+=都干了哪些事？

测试代码

复制代码代码如下:

namespace Wolfy.DelegateDemo
{
    public delegate void ShowMsg(string msg);
    public delegate int MathOperation(int a, int b);
    class Program
    {
        static ShowMsg showMsg;
        static MathOperation mathOperation;
        static void Main(string[] args)
        {
            showMsg += ShowHello;
            showMsg += ShowHello1;
            showMsg("大家新年好啊");
            mathOperation += Add;  
            mathOperation += Multiply;
            int result = mathOperation(1, 2);
            Console.WriteLine(result.ToString());
            Console.Read();
        }
        static void ShowHello(string msg)
        {
            Console.WriteLine("哈喽：" + msg);
        }
        static void ShowHello1(string msg)
        {
            Console.WriteLine("哈喽1：" + msg);
        }
        static int Add(int a, int b)
        {
            return a + b;
        }
        static int Multiply(int a, int b)
        {
            return a * b;
        }
    }
}

你可以猜猜运行结果，如下图：

可以看到没有返回值的都输出了，有返回值的只输出了Mutiply的结果，那么+=内部做了哪些事？可以看一下反编译的代码：

复制代码代码如下:

using System;
namespace Wolfy.DelegateDemo
{
    internal class Program
    {
        private static ShowMsg showMsg;
        private static MathOperation mathOperation;
        private static void Main(string[] args)
        {
            Program.showMsg = (ShowMsg)Delegate.Combine(Program.showMsg, new ShowMsg(Program.ShowHello));
            Program.showMsg = (ShowMsg)Delegate.Combine(Program.showMsg, new ShowMsg(Program.ShowHello1));
            Program.showMsg("大家新年好啊");
            Program.mathOperation = (MathOperation)Delegate.Combine(Program.mathOperation, new MathOperation(Program.Add));
            Program.mathOperation = (MathOperation)Delegate.Combine(Program.mathOperation, new MathOperation(Program.Multiply));
            Console.WriteLine(Program.mathOperation(1, 2).ToString());
            Console.Read();
        }
        private static void ShowHello(string msg)
        {
            Console.WriteLine("哈喽：" + msg);
        }
        private static void ShowHello1(string msg)
        {
            Console.WriteLine("哈喽1：" + msg);
        }
        private static int Add(int a, int b)
        {
            return a + b;
        }
        private static int Multiply(int a, int b)
        {
            return a * b;
        }
    }
}