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Running Javascript after control's selected value has been set

Answer 1

+1 A:

If the second dropdown is initially enabled through javascript (I'm assuming this is during a javascript onchange, since you didn't specify), then clicking the back button to reload the previous postback will never enable it.

Mixing ASP.NET with classic javascript can be hairy. You might want to have a look at ASP.NET's Ajax implementation (or the third-party AjaxPanel control if you're forced to use an older ASP.NET version). Those will give you the behaviour that you want through pure C#, without forcing you to resort to javascript hackery-pokery.

DannySmurf 2008-08-13 00:16:51

Answer 2

+1 A:

<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;

<script runat="server">
    protected void indexChanged(object sender, EventArgs e)
    {
        Label1.Text = " I did something! ";
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml"&gt;
<head runat="server">
    <title>Test Page</title>
</head>
<body>
    <script type="text/javascript">
        function firstChanged() {
            if(document.getElementById("firstSelect").selectedIndex != 0)
                document.getElementById("secondSelect").disabled = false;
            else
                document.getElementById("secondSelect").disabled = true;
        }
    </script>
    <form id="form1" runat="server">
    <div>
        <select id="firstSelect" onchange="firstChanged()">
            <option value="0"></option>
            <option value="1">One</option>
            <option value="2">Two</option>
            <option value="3">Three</option>
        </select>
        <select id="secondSelect" disabled="disabled">
            <option value="1">One</option>
            <option value="2">Two</option>
            <option value="3">Three</option>
        </select>
        <asp:DropDownList ID="DropDownList1" AutoPostBack="true" OnSelectedIndexChanged="indexChanged" runat="server">
            <asp:ListItem Text="One" Value="1"></asp:ListItem>
            <asp:ListItem Text="Two" Value="2"></asp:ListItem>    
        </asp:DropDownList>
        <asp:Label ID="Label1" runat="server"></asp:Label>
    </div>
    </form>
    <script type="text/javascript">
        window.onload = function() {firstChanged();}
    </script>
</body>
</html>

Edit: Replaced the whole code. This should work even in your user control. I believe that Register.ClientScriptBlock is not working because the code you write in that block is executed before window.onload is called. And, I assume (I am not sure of this point) that the DOM objects do not have their values set at that time. And, this is why you are getting selectedIndex as always 0.

Adhip Gupta 2008-08-13 00:53:34

Answer 3

A:

@DannySmurf: Yeah it's during the onChange event. Using Ajax is my fallback option, since everything else is working without it at the moment.

@Adhip: Thanks Adhip. That worked a treat. I'm still using RegisterStartupScript because of the way my control is structured, but it now adds a function to onload rather then executing straight away.

i.e.

Page.ClientScript.RegisterStartupScript(this.GetType(), "resetDropDowns", "window.onload=function(){ firstChanged();}", true);

Ray 2008-08-13 01:01:49

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Running Javascript after control's selected value has been set

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