如何保持我的Login.aspx页面的ReturnUrl参数覆盖我的ASP.NET登录控件的DestinationPageUrl属性？

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);

    if (!IsPostBack)
    {
        string returnUrl = Request.QueryString["ReturnUrl"];
        if (!string.IsNullOrEmpty(returnUrl))
        {
            Login1.DestinationPageUrl = returnUrl;
        }
    }
}

<asp:Login ID="Login1" runat="server" DestinationPageUrl="">

protected void Login1_LoggedIn(object sender, EventArgs e)
{
    string returnUrl = Request.QueryString["ReturnUrl"];
    if (!string.IsNullOrEmpty(returnUrl))
    {
        Response.Redirect(returnUrl);
    }
    else
    {
        Response.Redirect(FormsAuthentication.GetRedirectUrl(Login1.UserName, Login1.RememberMeSet));
    }
}