How can I do databinding with livedata?

Question

How can I do databinding with livedata?

activity_user_detail.xml:

Answer 1

This is a sample to figure out how LiveData and ObservableField works. You need to change T object and setValue() with LiveData, or set(T) with ObservableField. Changing properties of object T does not update UI.

ViewModel

public class UserViewModel extends ViewModel {

    public MutableLiveData userMutableLiveData = new MutableLiveData<>();
    private User mUser;

    public UserViewModel() {
        mUser = new User("User", "asd@abc.com");
        userMutableLiveData.setValue(mUser);

    }

    public void changeUserName() {

        // Both updates LiveData but does not update UI
        mUser.setName("Name is Changed");
        // userMutableLiveData.getValue().setName("Updated Name");

        // This one Updates UI
        //  userMutableLiveData.setValue(userMutableLiveData.getValue());
    }

    public void changeUser() {
        mUser = new User("New User Name", "myemail@mail.com");
        // Without setting new value UI is not updated and observe is not called
        userMutableLiveData.setValue(mUser);
    }
}

MainActivity

/*
    Without binding.setLifecycleOwner(this), liveData.setValue() does not update UI
    liveData.setValue() updates UI 
    EditText changes LiveData but does not update UI
 */
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        final ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        UserViewModel userViewModel = ViewModelProviders.of(this).get(UserViewModel.class);
        // LiveData should call setValue() to update UI via binding
        binding.setViewModel(userViewModel);

        // Required to update UI with LiveData
        binding.setLifecycleOwner(this);
    }
}

This code is for learning purposes.

Results you can get from this code:

1- Changing user name with changeUserName() updates the name of existing User of LiveData but does not update UI. UI gets updated when you rotate the device.

2- When you change User of LiveData and setValue() data-binding works.

3- Changing User properties using EditText 2-way binding android:text="@={viewModel.userMutableLiveData.name}" changes LiveData's User's name but does not update UI until device is rotated since User is still same.