尝试使用从Javascript到C＃的隐藏字段发送值

Question

I have a C#, ASP.NET Website, i have a JavaScript script inside it and i wish to send a var from inside of it to my code behind function, i tried to use a hidden field to do it, here's how it looks:

<asp:HiddenField ID="chatMessage" runat="server" />
<!--Script references. -->
<!--Reference the jQuery library. -->
<script src="Scripts/jquery-1.6.4.min.js" "></script>
<!--Reference the SignalR library. -->
<script src="/Scripts/jquery.signalR-2.0.0.js"></script>
<!--Reference the autogenerated SignalR hub script. -->
<script src="/signalr/hubs"></script>
<!--Add script to update the page and send messages.-->
<script type="text/javascript">
    $(function () {
        // Declare a proxy to reference the hub.
        var chat = $.connection.chatHub;
        // Create a function that the hub can call to broadcast messages.
        chat.client.broadcastMessage = function (name, message) {
            // Html encode display name and message.
            var encodedName = $('<div />').text(name).html();
            var encodedMsg = $('<div /> ').text(message).html();
            var tremp_id = $('<div /> ').text("<%=Request.QueryString["trempid"]%>").html();

            var chatMessage = document.getElementById('chatMessage');
            chatMessage.value = 'value from javascript';

            // Add the message to the page.
            $('#discussion').append('<li class="<%=returnLiClass(chatMessage.Value)%><strong>' + encodedName
                + '</strong>:&nbsp;&nbsp;' + encodedMsg + "Tremp:" + tremp_id + '</li>');
        };
        // Get the user name and store it to prepend to messages.
        $('#displayname').val('<%=returnName()%>');
        // Set initial focus to message input box.
        $('#message').focus();
        // Start the connection.
        $.connection.hub.start().done(function () {
            $('#sendmessage').click(function () {
                // Call the Send method on the hub.
                chat.server.send($('#displayname').val(), $('#message').val());
                // Clear text box and reset focus for next comment.
                $('#message').val('').focus();
            });
        });
    });
</script>

As you can see i send chatMessage.Value to my returnLiClass() function. When i debug i see it gets an empty string ("").

What am i doing wrong? Thank you!

Answer 1

When working with any server controls if you wish to reference them in javascript you have to use the ClientID.

It should look like the following:

var chatMessage = document.getElementById('<%= chatMessage.ClientID %>');

Answer 2

试试jquery

$('#chatMessage').val(chatMessage.value)