Help. Value of .Text not updating on "_KeyPress" event

Question

I'm trying to parse input to a textbox in real time.

I'm trying to restrict input to digits from 1 to 9 (no zeros). When the form loads, it pre-fills with the last used entry.

But if the user backs over it to change it, the value of ".Text" is still the initial loaded entry.

Private Sub tbxID_KeyPress(sender As Object, e As KeyPressEventArgs) Handles tbxID.KeyPress
     If e.KeyChar.ToString = vbBack Then e.Handled = False
     If e.KeyChar.ToString < "1" Or e.KeyChar.ToString > "9" Then e.Handled = True ' Anything but a number, ignore.
     ....
     ' Read the value of tbxID.Text. If backed over, it should return "" but doesn't. Still returns org value.

I tried "tbxID.Update()" and "tbxID.Refresh()", but neither had any effect (or is that "affect"?)

TIA

Answer 1

The contents of the input key are not reflected in the KeyPress event. You need to predict the string after it is reflected.

Use SelectionStart and SelectionLength properties to separate the text to the left and right. When you enter a normal character, reflected text will be left + input character + right.

Private Sub tbxID_KeyPress(sender As Object, e As KeyPressEventArgs) _
                                Handles tbxID.KeyPress
    If e.KeyChar = vbBack Then
        e.Handled = False
        Return
    End If
    If e.KeyChar < "1"c Or e.KeyChar > "9"c Then
        e.Handled = True
        Return
    End If
    Dim tbox As TextBox = DirectCast(sender, TextBox)
    Dim prevText As String = tbox.Text
    Dim leftStr As String = prevText.Substring(0, tbox.SelectionStart)
    Dim rightStr As String =
        prevText.Substring(tbox.SelectionStart + tbox.SelectionLength)
    Dim reflectedText As String = leftStr & e.KeyChar & rightStr
End Sub

Answer 2

Replace KeyPress with KeyDown. This stops backspace key and Del key.

    Private Sub tbxID_KeyDown(sender As Object, e As KeyEventArgs) Handles tbxID.KeyDown
        Dim tb As TextBox = DirectCast(sender, TextBox)
        If e.KeyCode = Keys.Back Then
            'stop backspace 
            tb.Text = tb.Text & " " 'add a space at end
            tb.Select(tb.TextLength - 1, 1) 'select the space
        ElseIf e.KeyCode = Keys.Delete Then
            'stop del
            tb.Text = tb.Text & " " 'add a space at end
            tb.Select(tb.TextLength - 1, 0) 'select before space
        ElseIf e.KeyCode > Keys.D0 AndAlso e.KeyCode <= Keys.D9 Then
            e.Handled = True
        End If
    End Sub