委托、事件--事件介绍篇

一、简单的事件介绍

      下面将直接在windows应用程序的一个窗体中说明事件的基本规则

1. using System;
2. using System.Windows.Forms;
3.  
4. namespace Forms
5. {
6.     public partial class Event : Form
7.     {
8.         /// <summary>
9.         /// 窗体构造器
10.         /// </summary>
11.         public Event()
12.         {
13.             InitializeComponent();
14.             // 使用+=即是把新方法添加到委托列表中--多播委托
15.             btnOne.Click += new EventHandler(btn_Click);
16.             btnTwo.Click += new EventHandler(btn_Click);
17.             btnTwo.Click += new EventHandler(btnTwo_Click);
18.             // 匿名委托
19.             btnOne.Click += delegate(object sender, EventArgs e) { labText.Text += "Button one was pressed"; };
20.         }
21.  
22.         /// <summary>
23.         /// 事件处理函数【没有返回值，命名规则为引发事件对象_事件名】
24.         /// </summary>
25.         /// <param name="sender"> 引发事件对象 </param>
26.         /// <param name="e"> 包含事件数据的对象 </param>
27.         private void btnTwo_Click(object sender, EventArgs e)
28.         {
29.             MessageBox.Show("This only happens in Button 2 click event");
30.         }
31.  
32.         /// <summary>
33.         /// 事件处理函数【没有返回值】
34.         /// </summary>
35.         /// <param name="sender"> 引发事件对象 </param>
36.         /// <param name="e"> 包含事件数据的对象 </param>
37.         private void btn_Click(object sender,EventArgs e)
38.         {
39.             labText.Text = ((Button)sender).Text + " was pressed";
40.         }
41.     }
42. }

二、生成事件

1. using System;
2. using System.Windows.Forms;
3.  
4. namespace Forms
5. {
6.     // 通过Button的Click事件激活自定义的事件
7.     public partial class CreateEvent : Form
8.     {
9.         BusEntity _busEntity = new BusEntity();
10.  
11.         // 定义委托--使用自定义的包含事件数据的对象
12.         public delegate void ActionEventHandler(object sender, ActionCancelEventArgs ev);
13.         // 定义事件
14.         public static event ActionEventHandler Action;
15.  
16.         public CreateEvent()
17.         {
18.             InitializeComponent();
19.             btnRaise.Click += new EventHandler(btnRaise_Click);
20.         }
21.  
22.         private void btnRaise_Click(object sender, EventArgs e)
23.         {
24.             ActionCancelEventArgs cancelEvent = new ActionCancelEventArgs();
25.             OnAction(this, cancelEvent);
26.             if (cancelEvent.Cancel)
27.                 labTest.Text = cancelEvent.Message + "--i = " + _busEntity.I;
28.             else
29.                 labTest.Text = _busEntity.TimeString + "--i = " + _busEntity.I;
30.         }
31.        
32.         protected void OnAction(object sender, ActionCancelEventArgs ev)
33.         {
34.             // 添加判断是否为空事件或事件未绑定处理函数
35.             if (Action != null)
36.                 // 触发事件
37.                 Action(sender, ev);
38.         }
39.     }
40.  
41.     #region 创建包含事件数据的对象
42.     /// <summary>
43.     /// 创建包含事件数据的对象
44.     /// </summary>
45.     public class ActionCancelEventArgs : System.ComponentModel.CancelEventArgs
46.     {
47.         string _msg = "";
48.  
49.         public ActionCancelEventArgs() : base() { }
50.  
51.         public ActionCancelEventArgs(bool cancel) : base(cancel) { }
52.  
53.         public ActionCancelEventArgs(bool cancel, string message)
54.             : base(cancel)
55.         {
56.             _msg = message;
57.         }
58.  
59.         public string Message
60.         {
61.             get { return _msg; }
62.             set { _msg = value; }
63.         }
64.     }
65.     #endregion
66.  
67.     public class BusEntity
68.     {
69.         public BusEntity()
70.         {
71.             CreateEvent.Action += new CreateEvent.ActionEventHandler(EventManager_Action);
72.         }
73.  
74.         // 委托调用的方法
75.         private void EventManager_Action(object sender, ActionCancelEventArgs ev)
76.         {
77.             ev.Cancel = !DoActions();
78.             if (ev.Cancel)
79.                 ev.Message = "Wasn't the right time.";
80.  
81.             i++;
82.         }
83.  
84.         private bool DoActions()
85.         {
86.             bool retVal = false;
87.             DateTime tm = DateTime.Now;
88.  
89.             if (tm.Second < 30)
90.             {
91.                 _time = "The time is " + DateTime.Now.ToLongTimeString();
92.                 retVal = true;
93.             }
94.             else
95.                 _time = "";
96.  
97.             return retVal;
98.         }
99.  
100.         #region 属性
101.         int i = 0;
102.         public int I
103.         {
104.             get { return i; }
105.             set { i = value; }
106.         }
107.         string _time = "";
108.         public string TimeString
109.         {
110.             get { return _time; }
111.         }
112.         #endregion
113.     }
114. }