This would enable the code to act on if something is shown. This could enable use cases like the one i'm currently working on:
I am building a frontend for domoticz (a home automation system). So when a device is shown in the menu as subtext or icon you want it to show the device status. But you don't want to retreive this status for all items in the list, only for the one showing on screen.
A onShowItem method would allow this... (retrieve that status when it's shown and then do a WatchUI.requestUpdate.
Without this callbackmethod this can only be acheived on the CustomMenu item class (by implementing it in the draw method). With this feature enable all subclasses for MenuItem and make the coding much easier..
