GUIBaseContext :: doBeforeEnter - Post-event handler after control gets focus

The handler is called when a control gets focus (GEV_Enter event). One may overload the handler in order to refresh control content. The handler should not be used for passing focus to other controls.

The GEV_Enter event is generated for the control receiving the focus and for all parents in the control hierarchy beginning with the topmost control in the hierarchy. In order to prevent the control from receiving focus, the handler may return an error (true or 1). For handling the case that the control has got focus without reacting, the doAfterEnter() handler might be overloaded.

• -1 (not handled) - the event handler will be removed from the handler list and is not called anymore.

• 1 (stop) - denies the event returning focus to the last active control
• 0 (ok) - Event handler terminated successfully.