What are the differences between ViewModel from the Jetpack library and the standard ViewModel in the MVVM architectural pattern?

ViewModel from the Jetpack library is a specific implementation of the MVVM pattern provided by Android Jetpack, which helps manage UI data considering the lifecycle of components (Activity, Fragment).

Main differences between Jetpack ViewModel and the abstract concept of ViewModel in MVVM:

• Lifecycle: Jetpack ViewModel is bound to the lifecycle of an Activity or Fragment and persists through their recreation (e.g., during screen rotation), preventing data loss.
• No direct UI connection: ViewModel does not contain references to Views, which prevents memory leaks.
• Integration with LiveData: Jetpack ViewModel is often used together with LiveData for reactive UI updates.
• State management: Jetpack ViewModel simplifies UI and business logic state management, separating them from the View.

In classic MVVM, ViewModel is just a layer between View and Model, without built-in lifecycle support and without standard tools for state preservation. Jetpack ViewModel is a ready-to-use component with support for Android-specific features.

Example of using Jetpack ViewModel:

class MyViewModel : ViewModel() {
    val data = MutableLiveData<String>()

    fun loadData() {
        data.value = "Hello from ViewModel"
    }
}

// In Activity or Fragment
viewModel.data.observe(viewLifecycleOwner) { value ->
    textView.text = value
}