How does the Android Viewmodel works internally, internal working of view model

Question

How does the Android Viewmodel works internally?

How Viewmodel save the data when the activity gets destroyed and recreated when the device get rotated

Answer 1

How does the Android Viewmodel works internally?

Android's ViewModel is designed to store and manage UI-related data in such a way that it can survive configuration changes such as screen rotations.

ViewModel gets called by an activity that previously called it, it re-uses the instance of that ViewModel object. However, if the Activity gets destroyed or finished, counterpart ViewModel calls the onClear() method for clearing up resources. Meaning if you have added something like this to your ViewModel :

override fun onClear() {
   super.onClear()
   clearAllLiveDataValues()
   disposeAllVariables() 
}

Function calls added here will be invoked.

How Viewmodel save the data when the activity gets destroyed and recreated when the device get rotated

ViewModel has its own lifecycle that allows itself to recover its state, and the transient data it holds, during screen rotations.

NOTE: Activity and ViewModel 's lifecycle are both ephemeral. Allowing the ViewModel to handle critical or sensitive data during configuration changes IS NOT RECOMMENDED .

Your application should use either shared prefs, secured storage (if necessary), local database or cloud storage when you are expected to handle critical or sensistive data in a specific screen or part of your app.

I recommend that you read the following:

• https://developer.android.com/topic/libraries/architecture/viewmodel
• https://android.jlelse.eu/android-architecture-components-a563027632ce
• https://medium.com/androiddevelopers/viewmodels-persistence-onsaveinstancestate-restoring-ui-state-and-loaders-fc7cc4a6c090