Question

I’m trying to update certain controls according to a selection in a dropdown list.

For example, in the “selectedIndexChanged” event of a dropDownList, if a user selects the value “sport-car” the text box “payload” is disabled and the textbox “max speed” is enabled.

    private sub dropDownList1_SelectedIndexChanged(byval sender as object, byval e as eventargs) handles dropDownList1.SelectedIndexChanged

    If dropDownList1.selectedValue = "sport-car" then

     textBox_payLoad.enabled = false
     textBox_maxSpeed.enabled = true

    end if

end sub

When I’m doing something like this, the controls aren’t enabled/disabled, even the event (wich I’ve added a breakpoint) seems not to be raised (sometimes several time after it is raised). Also, when the instructions in the condition is executed, nothing changes.

What am I doing wrong? Maybe this is a very easy issue, but I’m a begginer in MS Visual Web Developer.

Tags:

<%@ Page Title="" Language="vb" AutoEventWireup="false" MasterPageFile="~/Site.Master" CodeBehind="combo_atualizacao.aspx.vb" Inherits="taxasN4Web_v01.combo_atualizacao" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <asp:ScriptManagerProxy ID="ScriptManagerProxy1" runat="server">
    </asp:ScriptManagerProxy>
    <asp:UpdatePanel ID="UpdatePanel2" runat="server">
        <ContentTemplate>
            <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True">
                <asp:ListItem>sport-car</asp:ListItem>
                <asp:ListItem>pickup</asp:ListItem>
                <asp:ListItem>van</asp:ListItem>
                <asp:ListItem>bus</asp:ListItem>
                <asp:ListItem>motorcycle</asp:ListItem>
                <asp:ListItem></asp:ListItem>
            </asp:DropDownList>
            Payload
            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            &nbsp;Max Speed<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
        </ContentTemplate>
    </asp:UpdatePanel>
    <p>
    Payload 
    </p>
    <p>
    Max speed 
    </p>

</asp:Content>

Code-Behind (VB):

Public Class combo_atualizacao
    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
        If DropDownList1.SelectedValue = "sport-car" Then
            TextBox1.Enabled = False
            TextBox1.Enabled = True
        End If
    End Sub
End Class

Answer 1

Can you try adding the following to your update panel:

<asp:updatepanel>
<contenttemplate>
 ...
</contenttemplate>
<Triggers>
 <asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="SelectedIndexChanged" />
</Triggers>
</updatepanel>