How to get value from dynamically created texboxes? - vb.net

Question

im new here and im having some problem with my vb.net code. I have dynamically created few textboxes on panel, and I want my code after submitting the form to save those values into database. Problem is that I just cannot find the way how to grab values from those texboxes. I tried everything that i found on internet but i still getting the error message "Object reference not set to an instance of an object". Can someone advice me what am i doing wrong.
Here is the code how i created texboxes:
for i As Integer = 0 To cntPos -1
Dim txtJobTo as TextBox = new TextBox()
txtJobTo.ID = "txtJobTo_" & jobID
Dim label as Label = new Label()
label.text = posPanel.Rows(i).Item("Position")
pnlContainer.Controls.Add(label)
pnlContainer.Controls.Add(new LiteralControl("</td><td>"))
pnlContainer.Controls.Add(txtJobTo)
next
This line of code is shows those texboxes on page
<tr bgcolor="#FFCC99"><td colspan="4">
<asp:Panel ID="pnlContainer" runat="server" Visible="true"></asp:Panel></td></tr>
<tr><td colspan='6' align='center'> <asp:Button ID="cmdSave" Text="Save" ToolTip="cmdSave" CommandArgument="cmdSave_Click" runat="server" /></td></tr>
And this is part of the code that should save all data
Sub cmdSave_Click(ByVal sender As System.Object, e As EventArgs) Handles cmdSave.Click
...
for i As Integer = 0 To cntPosIns -1
Dim strTo as TextBox = New TextBox()
posID = posIns.Rows(i).Item("ID_Pos")
strTo.Text =CType(pnlContainer.FindControl("txtJobTo_" & posID.ToString()),TextBox).Text
....
'Insert into database
next
I always get error message on this line strTo.Text =CType(pnlContainer.FindControl("txtJobTo_" & posID.ToString()),TextBox).Text
Can someone please give me some advice on how to fix this? What is the proper way to read value from dynamically created textboxes in this situation?
Thank you

Answer 1

there are two aspects to this I think. Dynamic controls are a bit of a minefield and can take a while to understand.
a) Make sue to create the dynamic controls and add them to the page during OnInit or CreateChildControls. Access the value in the event handler or during OnPreRender...otherwise you will have trouble using the standard TextBox.Text property to get the value. It's tricky using dynamic controls because the values are not present for the whole page lifecycle without inspecting the page.request property.
b) Personally, when I dynamically create input elements, I don't "let go" of them and rely on findControl to get a handle back onto them for me.
When I create controls dynamically, I store them in a look up e.g. a lovely Dictionary(of string, TextBox) which is accessible to the rest of the code, e.g. a property or member variable.
' Lookup declared outside of the consuming methods so it is accessible to both
private dictControlsLookup as new dictionary(of string, textbox)
Sub YourSubName
for i As Integer = 0 To cntPos -1
Dim txtJobTo as TextBox = new TextBox()
txtJobTo.ID = "txtJobTo_" & jobID
Dim label as Label = new Label()
label.text = posPanel.Rows(i).Item("Position")
pnlContainer.Controls.Add(label)
pnlContainer.Controls.Add(new LiteralControl("</td><td>"))
pnlContainer.Controls.Add(txtJobTo)
dictControlsLookup.Add(txtJobTo.ID, textJobTo)
next
End Sub
Sub cmdSave_Click(ByVal sender As System.Object, e As EventArgs) Handles cmdSave.Click
...
for i As Integer = 0 To cntPosIns -1
Dim strTo as TextBox = New TextBox()
posID = posIns.Rows(i).Item("ID_Pos")
dim ctlId as string = "txtJobTo_" & posID.ToString()
If dictControlsLookup.ContainsKey(ctlId) Then
strTo.Text = dictControlsLookup(ctlId).Text
End If
....
'Insert into database
next
End Sub
Alternatively you could just iterate the dictControlsLookup.Values collection in save_click to access all the text boxes :-)