OK, this is pretty basic but I've read the documentation over and over and want to be sure I've got this right. In plain language, my watchkit app will be shut down by some user interaction exiting the app that's external to my code, right? I don't need to clear or reset the screen with any kind of close procedure that sets it up for another run? I don't need to build an "Exit" or "Close app" routine, right? It's confusing because the documentation implies the app will deactivate once it's no longer on screen (presumably by a user action like swiping to another app) and that this will call the didDeactivate function. But the documentation also claims:
In iOS Simulator, WatchKit calls the didDeactivate method for the current interface controller when you lock the simulator by selecting Hardware > Lock. When you subsequently unlock the simulator, WatchKit calls that interface controller’s willActivate method again. You can use this capability to debug your activation and deactivation code.
But the simulator doesn't appear to deallocate memory or reset variables or reset my app in any way. It remains persistent on screen in the state at the time of the lock, and it comes back in that state when I unlock. What worries me is that if I've got this wrong, I have an app built for one run. But I don't see routines for shutdown, screen clearance, or any of the elements you'd expect in a conventional shutdown routine.
I agree that the documentation can be confusing. The easiest way to think about it is that willActivate is called whenever your interface controller is displayed/activated. Likewise, didDeactivate is called whenever it is hidden/deactivated. So, if you're flipping through pages of controllers, each will receive a willActivate when it shows up and a didDeactivate when it disappears. Similarly, if a controller is deactivated because the app is no longer visible (e.g. it was suspended), didDeactivate will be called. If the user then raises their wrist to resume the app, willActivate is called, because the interface controller is being displayed.
There is no promise about whether your WatchKit app will be suspended or terminated (it's up to the OS), so you have to consider both possibilities. Based on experience, I know that dropping your arm will call didDeactivate before suspending your app. If you then raise your wrist, the app will resume and call willActivate. In my testing, the app was simply suspended (not terminated) in this situation.
You're correct that there is no built-in method that is called when the app is terminated. However, iOS 8.2 added four notifications that can be used to monitor the app/extension's state:
- NSExtensionHostDidBecomeActiveNotification
- NSExtensionHostDidEnterBackgroundNotification
- NSExtensionHostWillEnterForegroundNotification
- NSExtensionHostWillResignActiveNotification
来源：https://stackoverflow.com/questions/29635072/exit-from-a-watchkit-app-is-handled-by-the-watchkit-os-itself-i-dont-need-to-c