Callback function of keypad event handler. Register this callback with vm_keypad_register_event_callback to receive key events processed by underlying framework. The underlying system framework may process special key codes such as power key. Developers may choose to intercept the key code by returning non-zero values in this callback function, or bypassing the key code to system framework by returning 0.
This event handler should return non-zero values if application has
processed the key event and don't want to pass the key event to the
Return 0 to bypass this key event to underlying system framework.