在ASP.NET c＃代码隐藏中没有获得HTML输入类型的价值

Question

I got the process of getting the value of input field in c# in here:

Get value from input html in codebehind c#

I have a hidden input field in my aspx page like this:

<input type="hidden" id="lblCountry_val" runat="server" />

Where the value of the hidden field is put through jquery:

<script type="text/javascript">
$(function () {
        BindUserInfo();
    })


function BindUserInfo()
{
 document.getElementById('lblCountry_val').value = window.strcountry;
 }
</script>
<script type="text/javascript" src="http://smart-ip.net/geoip-json?callback=GetUserInfo"></script>

But When I am trying to get the value in Page_Load event in code behind with this: Response.Write(lblCountry_val.Value);

Nothing is being printed. How come?

EDIT I have done this by changing the hidden input field to an invisible textbox and then putting "name" attribute in the tag.

<input type="text" id="lblCountry_val" name="lblCountry_val" runat="server" style="display:none" />

And in the code behind:

var txt=Request.Form["lblCountry_val"];

Though I have not a clear idea how it was done.

Answer 1

You should write

document.getElementById('<%=lblCountry_val.ClientID%>')

This happens because in the most cases the serve side Id of a control is different from its clientId. The way to take it is the above.

Answer 2

First Method - In aspx, When you set a value to html field using Java script, Field's value doesn't appear in code behind file(aspx.cs). So you have to do additional page post back for set a value to hidden field and then you can able to catch the value in code behind file.

Second Method - Using tag, submit hidden field data to relevant aspx page.Then you can catch the value using Request.Form["lblCountry_val"] array.

Answer 3

Try this...

JavaScript

<script>
    $(document).ready(function () {
        var test = "1";
        $("<%=hdn_audio_length.ClientID%>").val(test);
    });
</script>

Html 

<asp:HiddenField runat="server" ID="hdn_audio_length" />
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="button1" runat="server" Text="Click" OnClick="button1_Click" />

C#

protected void button1_Click(object sender, EventArgs e)
{
    TextBox1.Text = hdn_audio_length.Value;
}

Answer 4

Here's an example setting hidden fields on submit click.

`<script>
    $(document).ready(function () {
        $("#submit").click(function () {
            $("#<%= ccnum.ClientID%>").val($("#cc-num").val());
            $("#<%= expdate.ClientID%>").val($("#cc-exp").val());
            $("#<%= cvc.ClientID%>").val($("#cc-cvc").val());
        });
    });
</script>`