The handler to call when the user is done composing a post.
- iOS 6.0+
The handler has a single parameter that indicates whether the user finished or cancelled composing the post. This block is not guaranteed to be called on any particular thread.
In iOS 6 and earlier, if you set a completion handler then your completion handler is responsible for dismissing the
dismiss(animated:. In iOS 7 and later when compiled with the iOS 7 or later SDK you must not dismiss the
SLCompose in your completion handler—the system will do so automatically.