Question

I’ve created a new tabpage and also added a richtextbox to it:

Private Sub AddTab(ByVal ctrl As TabControl, _
                              ByVal text As String)
    If Me.InvokeRequired Then
        Me.Invoke(New AddTabDelegate(AddressOf AddTab), _
                  New Object() {ctrl, text})
        Return
    End If

    Dim NewTab As New TabPage
    NewTab.Name = "OutputTab" & outputs.Item(outputs.Count - 1)
    NewTab.Text = "Domain"
    Dim NewTextbox As New RichTextBox
    NewTextbox.Name = "OutputTextbox" & outputs.Item(outputs.Count - 1)

    ctrl.Controls.Add(NewTab)
    NewTab.Controls.Add(NewTextbox)
End Sub

Now I try to access the richtextbox somewhere else in the code:

Dim NewTextbox As RichTextBox
NewTextbox = Me.Controls.Item("OutputTextbox" & current_output)
debug.print(NewTextbox.name)

I get the following error:

A first chance exception of type 'System.NullReferenceException' occurred in program.exe

I know the name is rigth cause I have printed the name in the create method and I have printed the name string in the code where I try to access it.

So by the looks of it it seems .Item() is not the right way to access the control.

So how to access to dynamically created control?

Answer 1

You are adding the dynamic control to a container by name ctrl and later looking for it in the form container. You can search recursively using Me.FindControl() but in your case, since you know the container that has the RichTextBox, it would be more efficient to do something as shown below.

Try

Dim NewTextbox As RichTextBox
Dim NewTab as TabPage
NewTab = ctrl.Controls.Item("OutputTab" & current_output)
NewTextbox = newTab.Controls.Item("OutputTextbox" & current_output)

debug.print(NewTextbox.name)