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:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5
 6 namespace CustomEventsDemo
 7 {
 8     public class CustomEventArgs:EventArgs
 9     {
10         //自定义字段用于存储值
11         public object Tag;
12         public string Message;
13         public CustomEventArgs()
14         {
15
16         }
17         public CustomEventArgs(string message, object tag)
18         {
19             Message = message;
20             Tag = tag;
21         }
22     }
23 }

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:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.ComponentModel;
 4 using System.Data;
 5 using System.Drawing;
 6 using System.Linq;
 7 using System.Text;
 8 using System.Windows.Forms;
 9
10 namespace CustomEventsDemo
11 {
12     public partial class FormPublisher : Form
13     {
14         //定义两个事件
15         public event EventHandler<CustomEventArgs> customEvent;
16         public event EventHandler<CustomEventArgs> customSecondEvent;
17         public FormPublisher()
18         {
19             InitializeComponent();
20         }
21
22         private void FormWithCutomEvent_Load(object sender, EventArgs e)
23         {
24             //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
25             if (customEvent != null)
26             {
27                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
28                 customEvent(this, customEventArgs);
29             }
30             if (customSecondEvent != null)
31             {
32
33                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");
34                 customSecondEvent(this, customEventArgs);
35             }
36
37         }
38
39         private void button1_Click(object sender, EventArgs e)
40         {
41
42             this.textBox2.AppendText(this.textBox1.Text + "\r\n");
43             //this.textBox1.Text = "";
44             if (customSecondEvent != null)
45             {
46                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");
47                 //触发事件
48                 customSecondEvent(this, customEventArgs);
49             }
50             if (customEvent != null)
51             {
52                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
53                 //触发事件
54                 customEvent(this, customEventArgs);
55             }
56         }
57     }
58 }

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:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.ComponentModel;
 4 using System.Data;
 5 using System.Drawing;
 6 using System.Linq;
 7 using System.Text;
 8 using System.Windows.Forms;
 9
10 namespace CustomEventsDemo
11 {
12     public partial class FormSubscriber : Form
13     {
14         FormPublisher form = null;
15        public FormSubscriber()
16         {
17             InitializeComponent();
18             //启动2个窗体
19             form = new FormPublisher();
20             form.Visible = true;
21            //订阅事件
22             form.customSecondEvent += form_customSecondEvent;
23            //订阅事件
24             form.customEvent += form_customEvent;
25            //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
26             FormSubScriber2 from2 = new FormSubScriber2(form);
27             from2.Visible = true;
28         }
29
30        void form_customSecondEvent(object sender, CustomEventArgs e)
31        {
32            this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "\r\n");
33        }
34
35        void form_customEvent(object sender, CustomEventArgs e)
36        {
37            this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "\r\n");
38        }
39
40         private void FormSubscriber_Load(object sender, EventArgs e)
41         {
42
43         }
44     }
45 }

　　另一个窗体也进行订阅:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.ComponentModel;
 4 using System.Data;
 5 using System.Drawing;
 6 using System.Linq;
 7 using System.Text;
 8 using System.Windows.Forms;
 9
10 namespace CustomEventsDemo
11 {
12     public partial class FormSubScriber2 : Form
13     {
14
15         public FormSubScriber2()
16         {
17             InitializeComponent();
18         }
19         public FormSubScriber2(FormPublisher form)
20         {
21             InitializeComponent();
22             //订阅form自定义事件
23             form.customEvent += form_customEvent;
24         }
25         void form_customEvent(object sender, CustomEventArgs e)
26         {
27             this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "\r\n");
28         }
29
30         private void FormSubScriber2_Load(object sender, EventArgs e)
31         {
32
33         }
34     }
35 }