C#自定义事件：属性改变引发事件示例

  1 using System;
  2 using System.Collections.Generic;
  3 using System.Linq;
  4 using System.Text;
  5 
  6 namespace ConsoleApplication15
  7 {
  8     class Program
  9     {
 10         static void Main(string[] args)
 11         {
 12             Monitor m = new Monitor();
 13             m.PropertyChanging += new Monitor.EventHandler(m_PropertyChanging);
 14             m.Year = 2014;
 15             m.Year = 1890;
 16             m.Year = 2013;
 17 
 18         }
 19 
 20         static bool First=false;
 21         static void m_PropertyChanging(object sender, PropertyChangingEventArgs e)
 22         {
 23             if (First==false)
 24             {
 25                 First = true;
 26             }
 27             else
 28             {
 29                 if (e.NewValue < 1900 || e.NewValue > 3000)
 30                 e.Cancel = true;
 31             }
 32         }
 33     }
 34 
 35     //（属性正在改变的时候）事件数据
 36     class PropertyChangingEventArgs : EventArgs
 37     {
 38         //构造函数
 39         public PropertyChangingEventArgs(string PropertyName, int OldValue, int NewValue)
 40         {
 41             _PropertyName = PropertyName;
 42             _OldValue = OldValue;
 43             _NewValue = NewValue;
 44         }
 45 
 46         //存储数据
 47         private string _PropertyName;
 48         private int _OldValue;
 49         private int _NewValue;
 50         private bool _Cancel;
 51 
 52         //获取或设置属性
 53         public string PropertyName
 54         {
 55             set
 56             {
 57                 _PropertyName = value;
 58             }
 59             get
 60             {
 61                 return _PropertyName;
 62             }
 63         }
 64         public int OldValue
 65         {
 66             set
 67             {
 68                 _OldValue = value;
 69             }
 70             get
 71             {
 72                 return _OldValue;
 73             }
 74         }
 75         public int NewValue
 76         {
 77             set
 78             {
 79                 _NewValue = value;
 80             }
 81             get
 82             {
 83                 return _NewValue;
 84             }
 85         }
 86         public bool Cancel
 87         {
 88             set
 89             {
 90                 _Cancel = value;
 91             }
 92             get
 93             {
 94                 return _Cancel;
 95             }
 96         }
 97     }
 98 
 99     class Monitor
100     {
101         //定义委托
102         public delegate void EventHandler(object sender, PropertyChangingEventArgs e);
103         //定义事件
104         public event EventHandler PropertyChanging;
105         
106         //事件处理（用属性方法）
107         int _YearValue;
108         public int Year
109         {
110             get
111             {
112                 return _YearValue;
113             }
114             set
115             {
116                 if (_YearValue != value)
117                 {
118                     if (PropertyChanging != null)
119                     {
120                         PropertyChangingEventArgs e = new PropertyChangingEventArgs("Year", _YearValue, value);
121                         PropertyChanging(this, e);
122                         if (e.Cancel)
123                         {
124                             return;
125                         }
126                         else
127                         {
128                             _YearValue = value;
129                         }
130                     }
131                 }
132             }
133         }
134     }
135 
136 }