What is the role of the ViewModel in the structure of Android apps and how does its lifecycle differ from the Activity's?

Short answer

It separates UI data and logic from the screen's lifecycle, and stays alive in memory while the Activity is recreated on device rotation, ending only when the screen is permanently closed.

Explanation

The ViewModel is created by ViewModelProvider and managed by a ViewModelStoreOwner. When a configuration change such as screen rotation occurs, the ViewModel is not destroyed but is re-attached to the new Activity instance. Its onCleared() is called only when the owner's real lifecycle ends (a call to finish() or the user leaving the back stack).

Code example

class UserViewModel : ViewModel() {
    private val _users = MutableStateFlow<List<User>>(emptyList())
    val users: StateFlow<List<User>> = _users.asStateFlow()

    override fun onCleared() {
        super.onCleared()
        // Clean up active resources and subscriptions
    }
}

Common mistakes

• Passing a reference to the Activity, a Context, or any View object into the ViewModel, which causes a certain memory leak.
• Creating a ViewModel instance manually through UserViewModel() instead of using ViewModelProvider or a Jetpack delegate (by viewModels()).

Follow-up questions

• What is the difference between LiveData and StateFlow and why is StateFlow preferred in modern Kotlin apps?

Sources

• Android Developers — ViewModel overview