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.NET Combo box - post back on change

Posted on 2011-03-18
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Last Modified: 2012-05-11
Hi I think its pretty straight forward what im trying to do - for a  aspx web page to post back the results of a selected combo box , I can do this with a button on the form but I would like to post back when the user has selected an item in the combo box, Iv seen other solutions that use a javascript on chnange event within the combo box but cant quite see how it works. Any help would be great!  
.net code

 Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Put user code to initialize the page here
        Dim t As Integer
        For t = 1 To 12
            DropDownList1.Items.Add("test " & t)
        Next t
    End Sub
HTML code
<%@ Page Language="vb" AutoEventWireup="false" Codebehind="WebForm1.aspx.vb" Inherits="KormaCom.WebForm1"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
	<HEAD>
		<title>WebForm1</title>
		<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
		<meta content="Visual Basic .NET 7.1" name="CODE_LANGUAGE">
		<meta content="JavaScript" name="vs_defaultClientScript">
		<meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
	</HEAD>
	<body MS_POSITIONING="GridLayout">
		<form id="Form1" method="post" runat="server">
			<asp:dropdownlist id="DropDownList1" style="Z-INDEX: 101; LEFT: 152px; POSITION: absolute; TOP: 72px"
				runat="server" Height="32px" Width="224px"></asp:dropdownlist></form>
	</body>
</HTML>

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Question by:MrDavidThorn
6 Comments
 
LVL 9

Accepted Solution

by:
jkofte earned 2000 total points
ID: 35164262
you should set the autopostback property of combobox to true and in events, create the selected index changed event.
0
 
LVL 10

Expert Comment

by:Asim Nazir
ID: 35164270
Set AutoPostback property of Combobox to true.
0
 
LVL 39

Expert Comment

by:Pratima Pharande
ID: 35164278
You want to post the seleted drop down value to next page or on same page button click ?

first of all you need to add postback condition in page_load
    Dim t As Integer
        If Page.IsPostBack = False Then
            For t = 1 To 12
                DropDownList1.Items.Add("test " & t)
            Next t
        End If

On same page on button click
  Response.Write(DropDownList1.SelectedItem.Value)
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LVL 10

Expert Comment

by:Asim Nazir
ID: 35164279
Do add If(!Ispostback) condition to your page load, so that combobox is loaded each time page postbacks.
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LVL 10

Expert Comment

by:Asim Nazir
ID: 35164280
Do add If(!Ispostback) condition to your page load, so that combobox is not loaded each time page postbacks.
0
 
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Expert Comment

by:John Claes
ID: 35164342
to ensure that a dropdown selection Change triggers a postBack you should add the AutoPostback to true.

This ensures that every change will do a PostBack.

But knowing the standard use of page_Load you're filling there the dropdown.
So you should indeed use the ( Page.IsPostBack) property to check.
if this is false this is the initial call for the page and the controls must be initialised.

I hope this was clear and understandable ;-)

regards
poor beggar
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