如何订阅Form的自定义事件

　　Window Form类有很多的属性/方法和事件,其中事件属于一种发布订阅模式 。订阅发布模式定义了一种一对多的依赖关系，让多个订阅者对象同时监听某一个主体对象。这个主体对象在自身状态变化时，会通知所有订阅者对象，使它们能够自动更新自己的状态。 当一个对象的改变需要同时改变其他对象，而且无需关心具体有多少对象需要改变时，就特别适合用此种模式。本文将演示如何在窗体上自定义一个事件(custom event) :

1 自定义一个CustomEventArgs类

　　一般自定义的事件都有一个参数,继承自EventArgs.此处我们自定一个CustomEventArgs,类中通过自定义字段来存储参数的值:

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

 namespace CustomEventsDemo
 {
     public class CustomEventArgs:EventArgs
     {
         //自定义字段用于存储值
         public object Tag;
         public string Message;
         public CustomEventArgs()
         {

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

2 自定义一个事件

　　接下来我们创建一个FormPublisher窗体,然后用 event EventHandler<CustomEventArgs> customEvent;event EventHandler<CustomEventArgs> customSecondEvent和来自定义两个custom Event事件,它们的事件参数为CustomEventArgs.在窗体加载事件中我们触发两个事件(这个顺序会影响在窗体加载时订阅者的事件响应顺序.如果我们创建一个窗体继承此FormPublisher的话,我们会在此窗体的事件面板中看到下图:

 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
     {
         //定义两个事件
         public event EventHandler<CustomEventArgs> customEvent;
         public event EventHandler<CustomEventArgs> customSecondEvent;
         public FormPublisher()
         {
             InitializeComponent();
         }

         private void FormWithCutomEvent_Load(object sender, EventArgs e)
         {
             //确定自定义事件的执行顺序,继承此窗体的子类窗体加载时的默认顺序
             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");
                 //触发事件
                 customSecondEvent(this, customEventArgs);
             }
             if (customEvent != null)
             {
                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
                 //触发事件
                 customEvent(this, customEventArgs);
             }
         }
     }
 }

3 订阅事件

　　下面定义一个FormSubscriber窗体来订阅自定义事件,我们要定义另一个窗体的事件,必须要先实例化那个窗体,否则会调用失败:

 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();
             //启动2个窗体
             form = new FormPublisher();
             form.Visible = true;
            //订阅事件
             form.customSecondEvent += form_customSecondEvent;
            //订阅事件
             form.customEvent += form_customEvent;
            //把发布窗体实例化后传入第二个订阅窗体中,否则不能订阅
             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)
         {

         }
     }
 }

　　另一个窗体也进行订阅:

 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 FormSubScriber2 : Form
     {

         public FormSubScriber2()
         {
             InitializeComponent();
         }
         public FormSubScriber2(FormPublisher form)
         {
             InitializeComponent();
             //订阅form自定义事件
             form.customEvent += form_customEvent;
         }
         void form_customEvent(object sender, CustomEventArgs e)
         {
             this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "\r\n");
         }

         private void FormSubScriber2_Load(object sender, EventArgs e)
         {

         }
     }
 }