/// <summary>
 /// 用户名输入框的焦点失去事件
 /// </summary>
 /// <param name="sender"></param>
 /// <param name="e"></param>
 private void text_manager_username_Leave(object sender, EventArgs e)
 {
     if (text_manager_username.Text != "")
     {
         if (mb.FindUserName(text_manager_username.Text).Count == 0)
         {
             lab_prompt.Text      = "该用户名可以使用";
             lab_prompt.ForeColor = Color.Green;
         }
         else
         {
             lab_prompt.Text      = "该用户名已被使用";
             lab_prompt.ForeColor = Color.Red;
         }
     }
 }