Is there any need to use onSaveInstanceState and onRestoreInstanceState when using Android Architecture Components LiveData & ViewModel?

Question

Android Architecture Components provide the LiveData and ViewModel classes which are more lifecycle-friendly and designed for a leaner Activity/Fragment. These classes handle storing data across configuration changes, but I'm confused about their use compared to the Activity framework APIs. Are onSaveInstanceState(Bundle) and onRestoreInstanceState(Bundle) still necessary or useful for preserving activity state?

Answer 1

onSaveInstanceState & onRestoreInstanceState is still useful.

ViewModel holds data only when process is alive.
But, onSaveInstanceState & onRestoreInstanceState can hold data even if process is killed.

ViewModel is easy to use and useful for preserving large data when screen orientation changes.
onSaveInstanceState & onRestoreInstanceState can preserve data when process is in background.(in background, app process can be killed by system at anytime.)

Answer 2

Assume a scenario : user is in activity A , then navigates to activity B

but because of low memory Android OS destroys activity A , therefor the ViewModel connected to it also destroys. (You can emulate it by checking Don't keep activities in Developer options)

now user navigates back to activity A, Android OS try's to create new Acivity and ViewModel objects. therefor you loosed data in ViewModel.

But still values in savedInstanceState are there.