Programming on BACKSPACE button

You need to consider selectedtext length too, as the behavior of backspace changes.

If TextBox1.SelectedText.Length > 0 Then
      TextBox1.Text = TextBox1.Text.Substring(0, TextBox1.SelectionStart) & TextBox1.Text.Substring(TextBox1.SelectionStart + TextBox1.SelectionLength)
    Else
      TextBox1.Text = TextBox1.Text.Substring(0, TextBox1.SelectionStart - 1) & TextBox1.Text.Substring(TextBox1.SelectionStart)
    End If

I think what you're writing is not a Virtual Keyboard at all.

If you assume that a target focused item is a TextBox, it means that you write some control to assist typing for your application only. My advice is: either rename you component or implement a real Virtual Keyboard.

To do this, you need just to things:

1) Use P/Invoke for Windows API SendInput.

2) Resolve the problem of keyboard focus and preventing both hiding and activation of you Virtual Keyboard, see this: Application focus getting and losing[^].

If you make this real thing, it will simulate normal user input, and your backspace problem will be solved simply by simulation of backspace key press. Mind you, backspace is not the only one, so better use the real technique instead of TextBox manipulations.

—SA

Dim d As Integer

If TextBox1.Text.Length > 0 Then
       d = TextBox1.Text.Length
       TextBox1.Text = TextBox1.Text.Remove(d - 1, 1)
End If