asp.net get html controls in code behind

Question

If I alter the html on a page using JavaScript, how can I access those changes in my ASP.NET code behind?

I found some dhtml "drag and drop" code online (http://www.dhtmlgoodies.com/scripts/drag-drop-nodes/drag-drop-nodes-demo2.html), but after moving list items from one control to another, I don't know how to "access" each control in the code behind so I can save the list items in each control.

I tried using the HTML Agility pack, but it seems like I'm only able to access the unaltered html - meaning all the controls are empty.

Any help/suggestions are appreciated. Or any suggestions as to a better way of accomplishing this are welcome (jQuery? Ajax Toolkit?).

EDIT: Here's some code. I'm able to populate an ASP Label control (_saveContent), from the JavaScript function saveDragDropNodes, with the "ul" ID and the corresponding "li" controls that I've dragged and dropped. When clicking the save button however, my Label control no longer contains any Text...

function saveDragDropNodes() {
        var saveString = "";
        var uls = dragDropTopContainer.getElementsByTagName('UL');
        for (var no = 1; no < uls.length; no++) {   // LOoping through all <ul>
            var lis = uls[no].getElementsByTagName('LI');
            for (var no2 = 0; no2 < lis.length; no2++) {
                if (saveString.length > 0) saveString = saveString + ";";
                saveString = saveString + uls[no].id + '|' + lis[no2].id;
            }
        }
        document.getElementById("<%=_saveContent.ClientID %>").innerHTML = saveString.replace(/;/g, ';<br>');
    }
  <div id="dhtmlgoodies_dragDropContainer">
    <div id="dhtmlgoodies_listOfItems">
        <div>
            <p>
                Available Items</p>
            <ul id="allItems" runat="server">
            </ul>
        </div>
    </div>
    <div id="dhtmlgoodies_mainContainer">
        <div>
            <p>
                Group 1</p>
            <ul id="_ul1">
            </ul>
        </div>
        <div>
            <p>
                Group 2</p>
            <ul id="_ul2">
            </ul>
        </div>
    </div>
    <asp:Label ID="_lSave" runat="server" ForeColor="Red" EnableViewState="false" />
</div>
<div id="footer">
<span onmouseover="saveDragDropNodes()">
    <asp:Button ID="_btnSave" runat="server" Text="Save Groups" OnClick="_btnSave_OnClick" /></span>
</div>
<ul id="dragContent">
</ul>
<div id="dragDropIndicator"></div>
<asp:Label ID="_saveContent" runat="server" />

Code Behind:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
    If Not Page.IsPostBack Then
        GetItems()
    End If
End Sub
Private Sub GetItems()
    Dim dt As DataTable = DbHelper.GetDataTableForSP("GetListOptions")
    Dim index As Integer = 1
    For Each _row As DataRow In dt.Rows
        Dim _li As New HtmlGenericControl("li")
        _li.ID = _row("ClassId")
        _li.Attributes.Add("runat", "server")
        _li.InnerHtml = String.Format("{0}) {1} {2}", index, _row("ClassId"), _row("ClassDescription1"))
        allItems.Controls.Add(_li)
        index += 1
    Next
End Sub
Private Sub SaveGroups()

    Dim str As String = _saveContent.Text /*No text here */
    _lSave.Text = "Groups Saved!"
    GetItems()
End Sub

Answer 1

The only content posted back to the server are values from form fields. See: Form submission.

You have two options:

1. Make use of ajax to pass the HTML from the client to the server.
2. Use a hidden input field to store the HTML just before the page posts back.

Here is an example of the latter:

Markup

<div id="content"></div>
<asp:HiddenField ID="hiddenContentField" runat="server" />
<asp:Button ID="button1" runat="server" Text="Post back" OnClick="button1_Click" OnClientClick="storeContent();" />

Script

function storeContent() {
    $('#<%= hiddenContentField.ClientID %>').val($('#content').html());
}

Any changes made in the content element will then be stored in the hidden input element and sent up to the server on postback.

Then in the code behind you can access the HTML passed up like so:

protected void button1_Click(object sender, EventArgs e)
{
    string html = hiddenContentField.Value;
}

Hope this helps.