委托-利用GetInvocationList处理链式委托-白红宇的个人博客

发布日期：2021-05-14 04:38:02 浏览次数：9 分类：博客文章

本文共 3952 字，大约阅读时间需要 13 分钟。

在利用委托进行函数代理的时候，我们习惯于用+=来把一个符合条件的委托加入委托链之中，如果加入了多个这样的函数，怎么一一对这些函数取返回值呢？请看下面的一个实例：

View Code

using System;namespace GetInvocationListDaemonCAPP{    public delegate string TestDelegate();    public class Program    {        static void Main(string[] args)        {            DelegateClass delegateClass = new DelegateClass();            TestMethodOne one = new TestMethodOne();            TestMethodTwo two = new TestMethodTwo();            TestMethodThree three = new TestMethodThree();            TestMethodFour four = new TestMethodFour();            delegateClass.testDelegate += one.Say;            delegateClass.testDelegate += two.Say;            delegateClass.testDelegate += three.Say;            delegateClass.testDelegate += four.Say;            delegateClass.InvokeDelegate();            Console.ReadKey();        }    }    public class DelegateClass    {        public TestDelegate testDelegate;        public void InvokeDelegate()        {            if (null != testDelegate)            {                string resultStr = testDelegate();                Console.WriteLine(resultStr);            }        }    }    public class TestMethodOne    {        public string Say()        {            return "You called me from TestMethodOne~~~";        }    }    public class TestMethodTwo    {        public string Say()        {            return "You called me from TestMethodTwo~~~";        }    }    public class TestMethodThree    {        public string Say()        {            return "You called me from TestMethodThree~~~";        }    }    public class TestMethodFour    {        public string Say()        {            return "You called me from TestMethodFour~~~";        }    }}

在这个示例中，我用了一个委托代理了四个类型相同，返回值相同的函数，那么当我要获取这些函数的返回值的时候，会得到什么样的结果呢？

You called me from TestMethodFour~~~

结果就是上面的输出，原来，像这种方式的委托操作，会保留最后一个输出，前面几个都被OverWrite掉了。

为了解决这个问题，GetInvocationList方法出现了。

View Code

using System;namespace GetInvocationListDaemonCAPP{    public delegate string TestDelegate();    public class Program    {        static void Main(string[] args)        {            DelegateClass delegateClass = new DelegateClass();            TestMethodOne one = new TestMethodOne();            TestMethodTwo two = new TestMethodTwo();            TestMethodThree three = new TestMethodThree();            TestMethodFour four = new TestMethodFour();            delegateClass.testDelegate += one.Say;            delegateClass.testDelegate += two.Say;            delegateClass.testDelegate += three.Say;            delegateClass.testDelegate += four.Say;            delegateClass.InvokeDelegate();            Console.ReadKey();        }    }    public class DelegateClass    {        public TestDelegate testDelegate;        public void InvokeDelegate()        {            if (null != testDelegate)            {                //遍历委托链表                foreach (Delegate dele in testDelegate.GetInvocationList())                {                    //类型转换                    TestDelegate delegateClass = (TestDelegate)dele;                                        //调用并 得到返回结果                    string resultStr = delegateClass();                    Console.WriteLine(resultStr);                }            }        }    }    public class TestMethodOne    {        public string Say()        {            return "You called me from TestMethodOne~~~";        }    }    public class TestMethodTwo    {        public string Say()        {            return "You called me from TestMethodTwo~~~";        }    }    public class TestMethodThree    {        public string Say()        {            return "You called me from TestMethodThree~~~";        }    }    public class TestMethodFour    {        public string Say()        {            return "You called me from TestMethodFour~~~";        }    }}

这样操作后，得到的运行结果如下：

You called me from TestMethodOne~~~You called me from TestMethodTwo~~~You called me from TestMethodThree~~~You called me from TestMethodFour~~~

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