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Editorial Team
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Asked: 2026-05-27T07:21:08+00:00

I was trying this from some time, but I am not able to get

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I was trying this from some time, but I am not able to get around it. Following is the code of the aspx page display:

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

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    Test<br />
    <asp:DropDownList ID="DropDownList1" runat="server">
        <asp:ListItem>1</asp:ListItem>
        <asp:ListItem>2</asp:ListItem>
    </asp:DropDownList>
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
        <ContentTemplate>
            <br />
            <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
    </ContentTemplate>
    </asp:UpdatePanel>
    </form>
</body>
</html>

Following is the code for the button1 click event:

Public Class WebForm1
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub

    Protected Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs) Handles DropDownList1.SelectedIndexChanged
        Label1.Text = DropDownList1.SelectedIndex

        UpdatePanel1.Update()

    End Sub
End Class

Could you please tell me what I missed out.

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1 Answer

  1. Editorial Team

    Set the autopostback to true in the drop down.

    The true means: everytime the value in the drop down changes, a postback to the server will occur.

    But listen to Tim Schmelter answer. If the drop down will not change, it’s a good idea to put it outside the update panel and the update panel must be triggered asynchronous by the drop down (if you don’t set a trigger to the update panel, every postback will update your updatepanel). If the content of the dropdown changes, put it inside the updatepanel.

    But like I said, I’m not using that for a long time, its a good idea to double check everything I say about the subject. =p

    PS: Microsoft Update Panels are easy to develop but make your site very slow. Try to learn about aspnet webservices and jQuery.

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