iOS Swift 如何监控 UIViewController 生命周期

Question

I am new to iOS development. So pardon me if this is a very basic thing.

From what I have learnt till now:

UIViewController class resembles somewhat equivalent to an Activity class in Android.

and viewDidLoad/viewWillAppear method to onCreate/onStart method

and viewDidAppear method to onResume method

Please correct me if I am wrong here.

Now, in Android we can monitor which of these methods(including other lifecycle methods) are triggered/called by implementing an Interface ( ActivityLifecycleCallbacks ) (somewhat resembling a protocol in iOS) which exists in the Application class in any Activity (particularly in a class which extends Application class).

It means that now these methods will be triggered/called whenever there is any navigation from one screen to another in the android app.

How do I do this in iOS using Swift? How do I know which screen(UIViewcontroller) the user is currently in and where he is navigating?

In short I want to write a standalone class which logs which screen(UIViewController) the user is currently in and which one of the lifecycle methods(viewDidLoad, viewWillAppear etc) is being executed?

Someone please help me out.

Edit:- I don't want them to subclass my standalone class instead of UIViewController class.

Answer 1

There are no global events that are fired when the UIViewController lifecycle methods are called. To create those you would need to subclass UIViewController as has been suggested.

You can look at UIApplication.sharedApplication().keyWindow?.rootViewController to get the current root view controller (which is often, but not always the currently active view controller).

You wouldn't typically design an app that depended on some central object tracking the state of view controllers.

The flow of UIViewController methods is pretty well described in the class reference and you can also work it out from the function names -

• viewDidLoad called after the view controller instance is loaded (once per instantiation)
• viewWillAppear called before this view appears
• viewDidAppear called after this view appears
• viewWillDisappear called before this view disappears
• viewDidDisappear called after this view disappears

Answer 2

Create a view controller subclass and add that implementation in there. Then make sure all the view controllers you create subclass that new class rather than UIViewController itself