Try not to remove notifications in viewWillDisappear: method,

Try not to remove notifications in viewWillDisappear: method,
1. The navigation controller side slide gesture is added to iOS7. When a side slide return is triggered, viewWillDisappear of the system is called. When the side slide return is canceled, viewWillAppear: method is called. 2. When performing a series of operations such as gestures and notifications, try to execute them in the dealloc method as much as possible, and add notifications as much as possible in one-time methods such as viewDidLoad. 3. When adding code to a system method that is called multiple times, such as viewWillAppear:, viewWillDisappear:, viewDidAppear:, and viewDidDisappear:, you must consider the business logic, to avoid unnecessary troubles.