如何實作Window Form上的自定義事件

 　　Window Form類有很多的屬性/方法和事件,其中事件屬于一種釋出訂閱模式 。訂閱釋出模式定義了一種一對多的依賴關系，讓多個訂閱者對象同時監聽某一個主體對象。這個主體對象在自身狀态變化時，會通知所有訂閱者對象，使它們能夠自動更新自己的狀态。 當一個對象的改變需要同時改變其他對象，而且無需關心具體有多少對象需要改變時，就特别适合用此種模式。本文将示範如何在窗體上自定義一個事件(custom event) : 

1 自定義CustomEventArgs類

一般自定義的事件都有一個參數,繼承自EventArgs.此處我們自定一個CustomEventArgs,類中通過自定義字段來存儲參數的值，示例代碼如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace CustomEventsDemo
{
    public class CustomEventArgs:EventArgs
    {
        //自定義字段用于存儲值
        public object Tag;
        public string Message;
        public CustomEventArgs()
        {

        }
        public CustomEventArgs(string message, object tag)
        {
            Message = message;
            Tag = tag;
        }
    }
}      

 2 自定義事件

 接下來我們建立一個FormPublisher窗體,然後用 event EventHandler<CustomEventArgs> customEvent;event EventHandler<CustomEventArgs> customSecondEvent和來自定義兩個custom Event事件,它們的事件參數為CustomEventArgs.在窗體加載事件中我們觸發兩個事件(這個順序會影響在窗體加載時訂閱者的事件響應順序.如果我們建立一個窗體繼承此FormPublisher的話,我們會在此窗體的事件面闆中看到下圖:

而窗體代碼如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CustomEventsDemo
{
    public partial class FormPublisher : Form
    {
        //定義兩個事件
        public event EventHandler<CustomEventArgs> customEvent;
        public event EventHandler<CustomEventArgs> customSecondEvent;
        public FormPublisher()
        {
            InitializeComponent();
        }

        private void FormWithCutomEvent_Load(object sender, EventArgs e)
        {
            //确定自定義事件的執行順序,繼承此窗體的子類窗體加載時的預設順序
            if (customEvent != null)
            {
                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
                customEvent(this, customEventArgs);
            }
            if (customSecondEvent != null)
            {

                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");
                customSecondEvent(this, customEventArgs);
            }

        }

        private void button1_Click(object sender, EventArgs e)
        {

            this.textBox2.AppendText(this.textBox1.Text + "\r\n");
            //this.textBox1.Text = "";
            if (customSecondEvent != null)
            {
                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");
                //觸發事件
                customSecondEvent(this, customEventArgs);
            }
            if (customEvent != null)
            {
                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
                //觸發事件
                customEvent(this, customEventArgs);
            }
        }
    }
}      

3 訂閱事件

下面定義一個FormSubscriber窗體來訂閱自定義事件,我們要定義另一個窗體的事件,必須要先執行個體化那個窗體,否則會調用失敗。示例代碼如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CustomEventsDemo
{
    public partial class FormSubscriber : Form
    {
        FormPublisher form = null;
       public FormSubscriber()
        {
            InitializeComponent();
            //啟動2個窗體
            form = new FormPublisher();
            form.Visible = true;
           //訂閱事件
            form.customSecondEvent += form_customSecondEvent;
           //訂閱事件
            form.customEvent += form_customEvent;
           //把釋出窗體執行個體化後傳入第二個訂閱窗體中,否則不能訂閱
            FormSubScriber2 from2 = new FormSubScriber2(form);
            from2.Visible = true;
        }

       void form_customSecondEvent(object sender, CustomEventArgs e)
       {
           this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "\r\n");
       }

       void form_customEvent(object sender, CustomEventArgs e)
       {
           this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "\r\n");
       }

        private void FormSubscriber_Load(object sender, EventArgs e)
        {

        }
    }
}      

執行示例代碼，窗體自定義事件訂閱效果如下：