Question

<script type="text/javascript">
    function getLocation() {
        if (navigator.geolocation) {
            navigator.geolocation.getCurrentPosition(getPostion);
        }
    }

    function getPostion(position) {
        var currentLat = position.coords.latitude;
        var currentLon = position.coords.longitude;
        alert(currentLat);
        document.forms[0].lat.value = "123";
        alert(document.forms[0].lat.value);
        document.forms[1].lon.value = currentLon;
        alert(document.forms[1].lon.value);
    }
</script>
<input type="hidden" name="lat">
<input type="hidden" name="lon">

<asp:TextBox ID="status" runat="server" CssClass="text" MaxLength="100" Columns="40" TextMode="MultiLine"></asp:TextBox>
<asp:Button ID="textSubmit" runat="server" CssClass="textSubmit" Text="submit" OnClientClick="getLocation()" OnClick="Post" />

protected void Post(object sender, EventArgs e)
    {
        string latitude = Request.Form["lat"].ToString();
        string longitude = Request.Form["lon"].ToString();

        string text = status.Text.Trim().ToString();//breakpoint here
        string connectionString = WebConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
        SqlConnection con = new SqlConnection(connectionString);
        try
        {
            con.Open();
            SqlCommand cmd = new SqlCommand("INSERT INTO [dbo].[Locations] VALUES('jshmqjw'," + Convert.ToDouble(latitude) + ", " + Convert.ToDouble(longitude) + ",CONVERT(varchar(100), GETDATE(), 20), 'text' )", con);
            cmd.ExecuteNonQuery();
        }
        catch (Exception err)
        {
            Response.Write("<script>alert('Error reading The database. " + err.Message + "') </script>");
        }
        finally
        {
            con.Close();
        }
    }

i want to send variable from javascript to C#.
i use hidden field to store value first and then in C# use request.form[“name”] to get the value. But after i set a breakpoint after one line, it turns out that the variables are null.
can anyone help!~

Answer 1

This should solve your problem:

Replace your html hidden fields with:

<asp:HiddenField ID="lat" runat="server"/>
<asp:HiddenField ID="lon" runat="server"/>

Then in your getPosition()-

document.getElementById('<%= lat.ClientID %>').value= currentLat ;
document.getElementById('<%= lon.ClientID %>').value= currentLon ;

And in code behind:

string latitude = lat.Value;
string longitude = lon.Value;