Geo位置的Javascript警报消息

Question

我正在尝试发出警告消息，如果用户没有共享其位置，则不应将纬度和经度空值插入数据库表。

JavaScript代码：

  <script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script>
<script type="text/javascript">
    if (navigator.geolocation) {
        navigator.geolocation.getCurrentPosition(success);
    } else {
        alert("Geo Location is not supported on your current browser!");
    }
    function success(position) {
        var lat = position.coords.latitude;
        var long = position.coords.longitude;
        var city = position.coords.locality;
        var myLatlng = new google.maps.LatLng(lat, long);
        var myOptions = {
            center: myLatlng,
            zoom: 12,
            mapTypeId: google.maps.MapTypeId.ROADMAP
        };
        var map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
        var marker = new google.maps.Marker({
            position: myLatlng,
            title: "lat: " + lat + " long: " + long
        });

        marker.setMap(map);
        var infowindow = new google.maps.InfoWindow({ content: "<b>User Address</b><br/> Latitude:" + lat + "<br /> Longitude:" + long + "" });

        document.getElementById("<%= latt.ClientID %>").value = position.coords.latitude;
        document.getElementById("<%= lng.ClientID %>").value = position.coords.longitude;

        var div = document.getElementById('map_canvas');
        div.style.visibility = 'hidden';

        infowindow.open(map, marker);
    }
</script>

我的ASP.NET页面加载方法：

protected void Page_Load(object sender, EventArgs e)
{
    var latt = this.latt.Value;
    var lng = this.lng.Value;

    ViewState["latt"] = latt.ToString();
    ViewState["lng"] = lng.ToString();
 }

ASP.NET HTML代码：

     <asp:HiddenField ID="latt" runat="server" />
      <asp:HiddenField ID="lng" runat="server" />


 <asp:ImageButton ID="ImageButton_Attendance_login" runat="server" Visible="false" 
   ImageUrl="~/images/Attendance_login.png" 
onclick="ImageButton_Attendance_login_Click"/>

我的按钮单击事件代码：

   protected void ImageButton_Attendance_login_Click(object sender, ImageClickEventArgs e)
{

    string Status = string.Empty;
    bo.Para1 = Session["Userid"].ToString();//UserId
    bo.Para2 = Session["Name"].ToString();//UserName
    bo.Para3 = this.Page.Request.ServerVariables["REMOTE_ADDR"];//IPAddress
    bo.Para4 = "";//City
    bo.Para5 = ViewState["latt"].ToString();//Latitude
    bo.Para6 = ViewState["lng"].ToString();//Longitude
    bo.Para7 = attendancetype;//SessionType
    bl.Insert_Branches_AttendanceInfo(bo, out Status);
    if (Status == "Success")
    {
     //   Response.Redirect("mypage.aspx");
     //   EmployeeAttendance(attendancetype);
      //  Response.Write("<script>alert('Thank You');</script>");
    }
    else
    if (Status == "NotShareLocation")
    {
        Response.Write("<script>alert('Please Share Your Location');</script>");


    }

  }