Question

I have a custom text box control which validates input (striped out unwanted chars). This works fine apart from when I also want to do further processing on an implementation of the control.

Example I have 3 “specialTextbox”s on a form. sText1, sText2 and sText3. sText1 & sText2 work as as intended. However, I need to make changes on the forum when the value of sText3 is changed, so I have a handler in the form to handle the ctext changed event:

Private Sub sText3(sender As Object, e As EventArgs) Handles sText3.TextChanged
  'do some stuff here
End Sub

However this routine appears to override the OnTextChanged method of the custom text box. I have tried includeing a call to MyBase.OnTextChanged, but this still doesn’t cascade up and no matter what I do I can’t seem to get the text box to do its validation duties.

Must be something really simple, but I’m stumped!

Here is a class which overrides textbox

Public Class restrictedTextBox
  Inherits Windows.Forms.TextBox

  Protected validChars As List(Of Char)

  Public Sub New(ByVal _validChars As List(Of Char))
    MyBase.New()

    validChars = _validChars
  End Sub

  Public Sub setValidChars(ByVal chrz As List(Of Char))
    validChars = chrz
  End Sub

  Protected Overrides Sub OnTextChanged(e As System.EventArgs)
    MyBase.OnTextChanged(e)

    Dim newValue As String = ""
    For Each c As Char In Me.Text.ToCharArray
      Dim valid As Boolean = False
      For Each c2 As Char In validChars
        If c = c2 Then valid = True
      Next

      If valid Then newValue &= c.ToString
    Next

    Me.Text = newValue
  End Sub
End Class

Here is a form which has a a custom textbox

Public Class frmNewForm
  Private Sub btnOK_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnOK.Click
      MessageBox.Show("the text from the restricted text is: " & txtRestricted.Text)
  End Sub
End Class

Here is a form with a custom text box, which implements the TextChanged event

Public Class frmNewForm2
  Private Sub btnOK_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnOK.Click
    MessageBox.Show("the text from the restricted text is: " & txtRestricted.Text)
  End If

 Private Sub txtRestricted_TextChanged(sender As Object, e As EventArgs) Handles txtRestricted.TextChanged
    'now that I have implemented this method, the restrictedTextBox.OnTextChanged() doesn't fire - even if I call MyBase.OnTextChanged(e)

    'just to be completely clear. the line of code below DOES get executed. But the code in restrictedTextBox.vb does NOT 
    lblAwesomeLabel.Text=txtRestricted.Text
  End Sub
End Class

Answer 1

It fires, but probably not the way you are implementing it.

Your sample code does not have an empty constructor for the textbox, which means you are most likely not using the designer when you are adding the textbox to the form.

But your form shows it was created by the designer:

Private Sub txtRestricted_TextChanged(sender As Object, e As EventArgs) _
  Handles txtRestricted.TextChanged
End Sub

That’s not possible with your posted code. If you are creating “new” controls programmatically, then you need to wire up the events programmatically, too.

Drop the handler and just leave the stub:

Private Sub txtRestricted_TextChanged(sender As Object, e As EventArgs)
  'yada-yada-yada
End Sub

then when you create a new textbox, wire it up:

txtRestricted = new restrictedTextBox(myCharsList)
AddHandler txtRestricted.TextChanged, AddressOf txtRestricted_TextChanged
Me.Controls.Add(txtRestricted)