How to retrieve a JavaScript variable within the codebehind of an ASP.NET application

Storing geolocation (lat,long) to a database table on page load is needed.

Here is the script used for this purpose:

<body onload="getLocation()">

    <p>Click the button to get your coordinates.</p>

            <%--<button onclick="getLocation()">Try It</button>--%>

            <p id="demo"></p>


    <form id="form1" runat="server">
        <div>

            <p>
                <asp:HiddenField ID="hdnLocation" ClientIDMode="Static" runat="server" />
 <asp:Label ID="lblloc" runat="server"></asp:Label>
                <asp:TextBox ID="txtloc" runat="server"></asp:TextBox>
                <asp:Button ID="btnLoc" text="submit" runat="server" OnClick="btnLoc_Click" />

            </p>
        </div>
    </form>

        <script>
            var x = document.getElementById("demo");

            function getLocation() {
                if (navigator.geolocation) {
                    navigator.geolocation.getCurrentPosition(showPosition);
                } else {
                    x.innerHTML = "Geolocation is not supported by this browser.";
                }
            }

            function showPosition(position) {
                x.innerHTML = "Latitude: " + position.coords.latitude +
                "<br>Longitude: " + position.coords.longitude;
                $("[id*=hdnLocation]").val(position.coords.latitude + ' ' + position.coords.longitude);
            //    $("[id*=btnLoc]").trigger("click");
            }
            </script>

</body>
</html>

The code behind includes:

public partial class getLocation : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) {

    lblloc.Visible = true;

    lblloc.Text = hdnLocation.Value;
    txtloc.Text = hdnLocation.Value;

}

When running the page, the hidden field values are visible in the browser inspection but cannot be accessed in the code behind. Response.Write returns blank and lblloc.text shows null. What could be causing this issue?

Answer №1

If you want your jQuery selector to function properly, it is crucial that the ClientIDMode property of your HTML element is set to "Static".

When dealing with server elements in .NET, it's important to understand that the server id and client id are distinct entities. Setting the ClientIDMode to "Static" will synchronize them for this specific element.

<asp:HiddenField ID="hdnLocation" runat="server" ClientIDMode="Static" />

Answer №2

Here's a solution that should do the job:

Creating an HTML form with script

<script type="text/javascript">
function setValue()
{
  var str = "value";
  document.getElementById("Hidden1").value = str;
}


</script>
<body>
    <form id="form1" runat="server">
    <div>
        <input id="Hidden1" type="hidden" runat="server" />
        <asp:Button ID="Button1" runat="server" OnClientClick="setValue()"  Text="Button"
            onclick="Button1_Click" />
    </div>
    </form>
</body>

Backend code snippet to retrieve the value

Response.Write(Hidden1.Value);

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