Is it enough to disable a toolbar button if the OS does not support the underlying functionality
Is it enough to disable a toolbar button if the OS does not support the underlying functionality such as the new Twitter Support in iOS 5 or do I have to remove it entirely from its toolbar?
The question is slightly subjective in that this is more of a design/user experience issue than anything else. I believe Apple may approve such an app, but you'll have to ask yourself this:
If you were a user and you saw a button that was never enabled. Would you fully understand why?
I would remove the button entirely for unsupported features - else it's like dangling a steak in front of a lion behind bars. Having a perpetually disabled buttons may confuse your users or cause them to be angry that they can't get this feature without upgrading or changing their device (in the case of differences between iPhone and iPod touch for example).