asp.net 服务器端控件中 弹出对话框 操作

HTML代码：
<script language="javascript" event="onclick" for="ImageButton1">
 return confirm('确定要保存变更吗？');//返回false时不执行ImageButton1_Click方法，返回ture时执行ImageButton1_Click方法
</script> 
 <asp:ImageButton ID="ImageButton1" runat="server" ImageAlign="AbsMiddle" ImageUrl="images/accept.gif" OnClick="ImageButton1_Click" />
C#代码：
/// <summary>
    /// 保存
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
    {
        
        string i = SaveData();
        if (i == "1")
        {
            this.HidSaveTorF.Value = "1";
        }
        else
        {
            this.HidSaveTorF.Value = "-1";
        }
    }