头一次手写这么长的代码，真累：

public delegate void DataInputEventHandler(object sender,EventArgs e);//如果你不重载EventArgs，此处不必做委托，用Event就可以了。
public class EventSource()
{
    public event DataInputEventHandler DataInputEvent;
    private void OnDataInputEvent(EventArgs e)
    {
          if(this.DataInputEvent!=null)//必须判断是否为null，否则如果事件监视方不监视此事件，则程序会出错
           {
                  this.DataInputEvent(this,e);
           }
    }
    public void AMethod()
   {
         //do something!
          ...
         this.OnDataInputEvent(new EventArgs());//激活事件;
         
   }
}
public class EventTarget()
{
      private EventSource source;
      public EventTarget()
     {
           this.source=new EventSource();
           source.DataInputEvent+=new DataInputEventHandler(this.DoThing);
     }
     protected void DoThing(object sender,EventArgs)
     {
           MessageBox.Show("开心警告：有数据录入了！");
      }

}
}
就这么简单