How do I validate text boxes with in a a group box using control

Question

So I know how to do just the textboxes. But the validation code will skip within a groupbox, because the control is not within the form. I was trying to somehow call the specific groupbox form but I don't know the exact syntax. Sorry I am new at this, if I don't have enough info please let me know. Also if you have references to control or groupbox commands it would be helpful. thanks!

For Each cntrl As Control In Controls
            If TypeOf cntrl Is TextBox Then
                cntrl.BackColor = Color.White
                If cntrl.Text = String.Empty Then
                    cntrl.BackColor = Color.Yellow
                    cntrl.Focus()
                    Return False
                End If

For Each cntrl As GroupBox In Controls
            If TypeOf cntrl Is TextBox Then
                cntrl.BackColor = Color.White
                If cntrl.Text = String.Empty Then
                    cntrl.BackColor = Color.Yellow
                    cntrl.Focus()
                    Return False
                End If

enter image description here

Answer 1

As per my comments, proper WinForms validation should look like this:

Private Sub TextBoxes_Validating(sender As Object, e As CancelEventArgs) Handles TextBox3.Validating,
                                                                                 TextBox2.Validating,
                                                                                 TextBox1.Validating
    Dim tb = DirectCast(sender, TextBox)

    If tb.TextLength = 0 Then
        tb.BackColor = Color.Yellow
        e.Cancel = True
    Else
        tb.BackColor = SystemColors.Window
    End If
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If ValidateChildren() Then
        'All controls contain valid data so go ahead and use it.
    End If
End Sub

You will now validate all the controls whose Validating event you handle, wherever they are located, and none that you don't. If you set CausesValidation to False on all the controls then no validation will occur until you call ValidateChildren . Even if you do want to validate as you go, you should still call ValidateChildren because that will ensure that even those controls that have never received focus will be validated.