C#自定义事件：属性改变引发事件示例

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

namespace ConsoleApplication15
{
    class Program
    {
        static void Main(string[] args)
        {
            Monitor m = new Monitor();
            m.PropertyChanging += new Monitor.EventHandler(m_PropertyChanging);
            m.Year = 2014;
            m.Year = 1890;
            m.Year = 2013;

        }

        static bool First=false;
        static void m_PropertyChanging(object sender, PropertyChangingEventArgs e)
        {
            if (First==false)
            {
                First = true;
            }
            else
            {
                if (e.NewValue < 1900 || e.NewValue > 3000)
                e.Cancel = true;
            }
        }
    }

    //（属性正在改变的时候）事件数据
    class PropertyChangingEventArgs : EventArgs
    {
        //构造函数
        public PropertyChangingEventArgs(string PropertyName, int OldValue, int NewValue)
        {
            _PropertyName = PropertyName;
            _OldValue = OldValue;
            _NewValue = NewValue;
        }

        //存储数据
        private string _PropertyName;
        private int _OldValue;
        private int _NewValue;
        private bool _Cancel;

        //获取或设置属性
        public string PropertyName
        {
            set
            {
                _PropertyName = value;
            }
            get
            {
                return _PropertyName;
            }
        }
        public int OldValue
        {
            set
            {
                _OldValue = value;
            }
            get
            {
                return _OldValue;
            }
        }
        public int NewValue
        {
            set
            {
                _NewValue = value;
            }
            get
            {
                return _NewValue;
            }
        }
        public bool Cancel
        {
            set
            {
                _Cancel = value;
            }
            get
            {
                return _Cancel;
            }
        }
    }

    class Monitor
    {
        //定义委托
        public delegate void EventHandler(object sender, PropertyChangingEventArgs e);
        //定义事件
        public event EventHandler PropertyChanging;
        
        //事件处理（用属性方法）
        int _YearValue;
        public int Year
        {
            get
            {
                return _YearValue;
            }
            set
            {
                if (_YearValue != value)
                {
                    if (PropertyChanging != null)
                    {
                        PropertyChangingEventArgs e = new PropertyChangingEventArgs("Year", _YearValue, value);
                        PropertyChanging(this, e);
                        if (e.Cancel)
                        {
                            return;
                        }
                        else
                        {
                            _YearValue = value;
                        }
                    }
                }
            }
        }
    }

}