onActivityResult() 可以在 onCreate() 之前调用吗？

Question

Can onActivityResult() theoretically be called before onCreate ? I know it can be called before onResume() , but let's consider this extreme case:

1. activity A is running and starts activity B for a result
2. activity B opens
3. the device is running low on memory, so it destroys activity A
4. activity B finishes with a result

What happens now? Does activity A get re-created before receiving the result, or does it receive the result before onCreate() ? Is this guaranteed to be in the same order each time?

Answer 1

You will commonly see this if you are opening an app to scan a barcode or take a photo or video. The Activity you launch to do that requires a lot of resources so Android kills the OS process hosting your app.

When the Activity you launched wants to return the result to your app, the following occurs:

• Android creates a new OS process for your app (because it killed yours and needs a new one)
• Android instantiates the Application instance (or your app's custom one) and calls onCreate() on that
• Android instantiates a new instance of the Activity that will get the result (the one that called startActivityForResult() )
• Android calls onCreate() on the new Activity . The Bundle passed to onCreate() in this case is the Bundle most recently used to the save the Activity instance state (from onSaveInstanceState() ).
• Android calls onStart() on the new Activity
• Android calls onActivityResult() on the new Activity
• Android calls onResume() on the new Activity

Answer 2

Those case Use

registerForActivityResult()

Activity Result APIs decouple the result callback from the place in your code where you launch the other activity. As the result callback needs to be available when your process and activity are recreated, the callback must be unconditionally registered every time your activity is created, even if the logic of launching the other activity only happens based on user input or other business logic

more details refer Getting a result from an activity