Textbox SelectAll on tab but not mouse click

Question

So lets say I have a WPF form with several text boxes, if you tab to the text box and it already has something in it, I want to select all the text in that box so typing wil

Answer 1

You could capture the last key pressed and compare against it in your event

private Key lastKey;
protected override void OnKeyDown(KeyEventArgs e)
{
     lastKey = e.Key;
     base.OnKeyDown(e);
}

and in your event:

private void EventSetter_OnHandler(object sender, RoutedEventArgs e)
{
    if(lastKey != Key.Tab)
        return;

    TextBox txt = sender as TextBox;
    if (txt != null) txt.SelectAll();
}

It's not perfect because they could have hit tab (not tabbing into your control) and than click into it your control. But it will work most of the time.