Integrating Drag & Drop with Web Forms

Discussion in 'ASP .Net Web Controls' started by Ed Dennison, Nov 26, 2003.

  1. Ed Dennison

    Ed Dennison Guest

    I am trying to create a simple ASP.NET web page that includes a list
    box into which my user can drag and drop URLs. I want the user to be
    able to easily build a list of URLs by dragging and dropping links
    from other pages onto my page (and also dragging the link from IE's
    Address bar).

    This is what my index.aspx file looks like (in HTML view):

    <%@ Page language="c#" Codebehind="index.aspx.cs"
    AutoEventWireup="false" Inherits="rdmgr.WebForm1" %>
    <HTML>
    <HEAD>
    <title>WebForm1</title>
    <SCRIPT language="javascript">
    function SetText()
    {
    window.event.returnValue = false;
    window.event.dataTransfer.dropEffect = "copy";
    var opto = new Option(window.event.dataTransfer.getData("Text"));
    window.document.Form1.Select1.add (opto);
    }
    function OverDrag()
    {
    window.event.returnValue = false;
    }
    </SCRIPT>
    </HEAD>
    <body MS_POSITIONING="GridLayout">
    <form id="Form1" method="post" runat="server">
    <asp:Button id="Button1" style="Z-INDEX: 101; LEFT: 736px;
    POSITION: absolute; TOP: 88px" runat="server"
    Text="Button" Width="74px" Height="32px"></asp:Button>
    <SELECT id="Select1" style="Z-INDEX: 103; LEFT: 160px; WIDTH:
    480px; POSITION: absolute; TOP: 88px; HEIGHT: 280px"
    size="17" name="Select1" runat="server" ondrop="SetText()"
    ondragover="OverDrag()">
    <OPTION></OPTION>
    </SELECT>
    </form>
    </body>
    </HTML>

    The web page behaves exactly as I desire: when I drag links or URLs
    into the list box, the link text is added to the list. Perfect.

    The problem is, that from the point of view of the C# code, nothing is
    inside the listbox. Specifically, when I handle the Click event for my
    button, the Select1 object has no Items. Also, if I refresh the web
    page, the list contents disappear. And finally, the
    Select1_ServerChange event does not fire when I drag items into the
    list.

    I assume that I am missing some critical piece of glue that causes the
    client side activity in the javascript function to get dispatched to
    the server side. Can anyone tell me what I need to do?

    Thank you!

    Ed Dennison
    E-mail: ed at cognex dot com
    Ed Dennison, Nov 26, 2003
    #1
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