There is no state between page requests - every page gets recreated from scratch again. Your code that creates the controls should be created in
Page_Load. It might be easier for you to create the controls you need at design time, and set their Visible property to False if you don't need them.
There may be more clever ways to do this - I'd check in the dotnet.framework.aspnet forum or go directly to http://www.*-*-*.com/ .
>Content-Class: urn:content-classes:message
>Subject: Re: Dynamic creation of web controls in VB.NET
>Date: Tue, 20 May 2003 22:21:07 -0700
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>Thanks for your response.
>Actually, I created 2 static web controls (Panel and
>button named Start) in the web form with the code below:
>***** start of code *****
>Public Class WebForm1
> Inherits System.Web.UI.Page
> Protected WithEvents Panel As
>System.Web.UI.WebControls.Panel
> Protected WithEvents ddl1 As New DropDownList()
> Protected WithEvents ddl2 As New DropDownList()
> Protected WithEvents btnStart As
>System.Web.UI.WebControls.Button
> Protected WithEvents txt As New TextBox()
>#Region " Web Form Designer Generated Code "
> 'This call is required by the Web Form Designer.
> <System.Diagnostics.De{*filter*}StepThrough()> Private Sub
>InitializeComponent()
> End Sub
> Private Sub Page_Init(ByVal sender As System.Object,
>ByVal e As System.EventArgs) Handles MyBase.Init
> 'CODEGEN: This method call is required by the Web
>Form Designer
> 'Do not modify it using the code editor.
> InitializeComponent()
> End Sub
>#End Region
> Private Sub Page_Load(ByVal sender As System.Object,
>ByVal e As System.EventArgs) Handles MyBase.Load
> End Sub
> Private Sub Master_SelectedIndexChanged(ByVal sender
>As System.Object, ByVal e As System.EventArgs)
> ddl2.Items.Clear()
> Select Case ddl1.SelectedItem.Value
> Case "A"
> ddl2.Items.Add("A1")
> ddl2.Items.Add("A2")
> Case "B"
> ddl2.Items.Add("B1")
> ddl2.Items.Add("B2")
> Case "C"
> ddl2.Items.Add("C1")
> ddl2.Items.Add("C2")
> End Select
> End Sub
> Private Sub Slave_SelectedIndexChanged(ByVal sender As
>System.Object, ByVal e As System.EventArgs)
> txt.Text = ddl2.SelectedItem.Value
> End Sub
> Private Sub btnStart_Click(ByVal sender As
>System.Object, ByVal e As System.EventArgs) Handles
>btnStart.Click
> ddl1.ID = "Master"
> ddl1.AutoPostBack = True
> ddl1.Items.Add("A")
> ddl1.Items.Add("B")
> ddl1.Items.Add("C")
> AddHandler ddl1.SelectedIndexChanged, AddressOf
>Me.Master_SelectedIndexChanged
> Panel.Controls.Add(ddl1)
> ddl2.ID = "Slave"
> ddl2.AutoPostBack = True
> AddHandler ddl2.SelectedIndexChanged, AddressOf
>Me.Slave_SelectedIndexChanged
> Panel.Controls.Add(ddl2)
> Panel.Controls.Add(txt)
> End Sub
>End Class
>***** end of code *****
>After pressing the "Start" button, 2 dropdownlist and 1
>textbox controls are created dynamically. However, after
>change the content of the dropdownlist control, all
>dynamic controls disappear. Could you please tell me why?
>Thanks.
>>-----Original Message-----
>>How are you creating the dropdownlist? Dynamically in
>code? If so, is the
>>object's scope broad enough (i.e. it should be declared
>on the class level
>>as Protected ddlWhatever as DropDownList, not on the
>procedure level)?
>>Have you actually instantiated the dropdownlist (using
>New)?
>>Sorry, I'm not sure if you have checked these things,
>maybe post some code
>>and it will be clearer what is going wrong.
>>> I have created a "dropdownlist" server control in a web
>>> application and want to add codes to it after making
>>> changes on its content. I find that I can't do that as
>the
>>> control ID cannot be recognized. Could you give me some
>>> hints? Thanks.
>>.
Dynamic creation of web controls in VB.NET