.Net （C#）委託和事件（擷取多個傳回值）

在講如何擷取多個傳回值之前先來看一個小例子：

 

        private void button1_Click(object sender, EventArgs e)
        {
            int Number = 200;         //設定Number的值為 200。
            Publishser pub = new Publishser();     //執行個體化Publishser
            Subscriber1 sub1 = new Subscriber1();     //執行個體化Subscriber1
            Subscriber2 sub2 = new Subscriber2();     //執行個體化Subscriber2
            Subscriber3 sub3=new Subscriber3();       //執行個體化Subscriber3
            pub.NumberChanged += sub1.OnNumberChanged;   //將方法綁定到委託
            pub.NumberChanged += sub2.OnNumberChanged;
            pub.NumberChanged += sub3.OnNumberChanged;
            pub.DoComething(Number);      //調用DoComething
        }

    class Publishser
    {
        public delegate int DemoEventHandler(int num);      //定義委託，可代表的方法類型是整形
        public event DemoEventHandler NumberChanged;  //申明事件
        public void DoComething(int temp)
        {
            if (NumberChanged != null)
            {
                 temp=NumberChanged(temp);
            }
            MessageBox.Show(temp.ToString());
        }
    }

    class Subscriber1
    {
        public int OnNumberChanged(int num)
        {
            MessageBox.Show("調用了Subscriber1類，num值為："+ num);
            return num + 100; ;
        }
    }

    class Subscriber2
    {
        public int OnNumberChanged(int num)
        {
            MessageBox.Show("調用了Subscriber2類 num值為："+num);
            return num+100;
        }
    }

    class Subscriber3
    {
        public int OnNumberChanged(int num)
        {
            MessageBox.Show("調用了Subcriber3類，num值為："+num);
            return num+100;
        }
    }

 

 

 

 我以為得到的結果是：

                              調用了Subscriber1類，num值為：200

                              調用了Subscriber2類，num值為：300

                              調用了Subscriber3類，num值為：400

                              500

但是程式運行完之後結果卻不是我所想的，結果是：

                                                                    調用了Subscriber1類，num值為：200

                                                                    調用了Subscriber2類，num值為：200

                                                                    調用了Subscriber3類，num值為：200

                                                                    300

發現問題之後我用逐語句啟動並執行方式偵錯工具，我發現當NumberChanged != null 第一次調用了Subscriber1之後並沒有返回到Publishser類，也沒有執行Subscriber1的 return，而是直接調用了Subscriber2，temp的值依舊是剛開始的200。執行完之後調用Subscriber3，只有當Subscriber3執行完了之後才返回到Publishser 這個時候temp的值等於300。（現在我也不知道為什麼會這樣，但是我在網上學習了一種可以擷取多個傳回值的方法！）

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擷取多個傳回值：

 

        private void button1_Click(object sender, EventArgs e)
        {
            int Number = 200;
            Publishser pub = new Publishser();
            Subscriber1 sub1 = new Subscriber1();
            Subscriber2 sub2 = new Subscriber2();
            Subscriber3 sub3=new Subscriber3();
            pub.NumberChanged += sub1.OnNumberChanged;
            pub.NumberChanged += sub2.OnNumberChanged;
            pub.NumberChanged += sub3.OnNumberChanged;
            pub.DoComething(Number);
        }

    class Publishser
    {
        public delegate int DemoEventHandler(int num);
        public event DemoEventHandler NumberChanged;
        public void DoComething(int temp)
        {
            if (NumberChanged != null)
            {
                Delegate[] delArray = NumberChanged.GetInvocationList();  
                foreach (Delegate del in delArray)
                {
                    DemoEventHandler method = (DemoEventHandler)del;
                    temp = method(temp);
                }
            }
            MessageBox.Show(temp.ToString());
        }
    }

    class Subscriber1
    {
        public int OnNumberChanged(int num)
        {
            MessageBox.Show("調用了Subscriber1類，num值為："+ num);
            return num + 100; ;
        }
    }

    class Subscriber2
    {
        public int OnNumberChanged(int num)
        {
            MessageBox.Show("調用了Subscriber2類 num值為："+num);
            return num+100;
        }
    }

    class Subscriber3
    {
        public int OnNumberChanged(int num)
        {
            MessageBox.Show("調用了Subcriber3類，num值為："+num);
            return num+100;
        }
    }

運行得到的結果是：

                              調用了Subscriber1類，num值為：200

                              調用了Subscriber2類，num值為：300

                              調用了Subscriber3類，num值為：400

                              500

 

現在就是我想到的結果了，利用Delegate 基類的GetInvocationList()靜態方法，可以得到委託鏈表，隨後遍曆委託鏈表依次執行，就可以得到每個方法的傳回值了。