int i=0; if (!int.TryParse(this.txtPage.Text, out i)) {    Response.Write("<script>alert('请输入有效数字！')</script>");    this.txtPage.Text = string.Empty;  }//判断是否是数字  

try         {             if (Convert.ToInt32(this.txtPage.Text) > totalPage || Convert.ToInt32(this.txtPage.Text)<1)             {                 ClientScript.RegisterClientScriptBlock(GetType(), "提示", "alert('请输入有效数字！')", true);             }             else             {               ViewState["pageindex"] = this.txtPage.Text;               GetData();             }         }         catch (Exception)         {            ClientScript.RegisterClientScriptBlock(GetType(), "提示", "alert('请输入有效数字！')", true);         }