How to update LiveData of a ViewModel from background service and Update UI

Question

Recently I am exploring Android Architecture, that has been introduced recently by google. From the Documentation I have found this:

public class MyViewModel extends ViewModel {     private MutableLiveData<List<User>> users;     public LiveData<List<User>> getUsers() {         if (users == null) {             users = new MutableLiveData<List<Users>>();             loadUsers();         }         return users;     }      private void loadUsers() {         // do async operation to fetch users     } } 

the activity can access this list as follows:

public class MyActivity extends AppCompatActivity {     public void onCreate(Bundle savedInstanceState) {         MyViewModel model = ViewModelProviders.of(this).get(MyViewModel.class);         model.getUsers().observe(this, users -> {             // update UI         });     } } 

My Question is, I am going to do this:

1. in the loadUsers() function I am fetching the data asynchronously where I will first check the database(Room) for that data

2. If I do not get the data there I will make an API call to fetch the data from the web server.

3. I will insert the fetched data into the database(Room) and update the UI according the data.

What is the recommended approach to do this?

If I start a Service to call the API from the loadUsers() method, how can I update the MutableLiveData<List<User>> users variable from that Service?

Answer 1

I am assuming that you are using android architecture components. Actually it doesn't matter wherever you are calling service, asynctask or handler to update the data. You can insert the data from the service or from the asynctask using postValue(..) method. Your class would look like this:

private void loadUsers() {     // do async operation to fetch users and use postValue() method     users.postValue(listOfData) } 

As the users is LiveData, Room database is responsible for providing users data wherever it is inserted.

Note: In MVVM like architecture, the repository is mostly responsible for checking and pulling local data and remote data.

Answer 2

You can use MutableLiveData<T>.postValue(T value) method from background thread.

private void loadUsers() {     // do async operation to fetch users and use postValue() method    users.postValue(listOfData) }