新增、删除事件

 数字计算时的用法： 

 private void MyButtonClick(object sender, System.EventArgs e)
  {
   try
   {
    lblAns.Text =(float.Parse(txtN1.Text) + float.Parse(txtN2.Text)).ToString();
   }
   catch
   {
   }
  }

  private void Form1_Load(object sender, System.EventArgs e)
  {
   txtN1.TextChanged += new EventHandler(MyButtonClick);
   txtN2.TextChanged += new EventHandler(MyButtonClick);

  }

  private void btnAdd_Click(object sender, System.EventArgs e) //"新增事件";
  {
   txtN1.TextChanged += new EventHandler(MyButtonClick);
   txtN2.TextChanged += new EventHandler(MyButtonClick);

  }

  private void btnDel_Click(object sender, System.EventArgs e) //"删除事件";
  {
   txtN1.TextChanged -= new EventHandler(MyButtonClick);
   txtN2.TextChanged -= new EventHandler(MyButtonClick);

  }