委托-利用GetInvocationList处理链式委托

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：

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。

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~~~