有条件地清空TextBox值

        /// <summary>
        /// 清空TextBox事件
        /// </summary>
        /// <param name="sender">事件对象</param>
        /// <param name="e">事件参数</param>
        protected void tb_name_PreRender(object sender, EventArgs e)
        {
            this.tb_name.Attributes.Add("onfocus","return this.value=(this.value=='请录入名称')?'':this.value");
        }