LiveData update on object field change

Solution 1:

I don't think there is any best practice as such recommended by android for this. I would suggest you to use the approach which uses cleaner & less boilerplate code.

If you are using android data binding along with LiveData you can go with the following approach:

Your POJO object would look something like this

public class User extends BaseObservable {
    private String firstName;
    private String lastName;

    @Bindable
    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
        notifyPropertyChanged(BR.firstName);
    }

    @Bindable
    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
        notifyPropertyChanged(BR.lastName);
    }
}

So you would be already having a class which notifies whenever its property changes. So you can just make use of this property change callback in your MutableLiveData to notify its observer. You can create a custom MutableLiveData for this

public class CustomMutableLiveData<T extends BaseObservable>
        extends MutableLiveData<T> {


    @Override
    public void setValue(T value) {
        super.setValue(value);

        //listen to property changes
        value.addOnPropertyChangedCallback(callback);
    }

    Observable.OnPropertyChangedCallback callback = new Observable.OnPropertyChangedCallback() {
        @Override
        public void onPropertyChanged(Observable sender, int propertyId) {

            //Trigger LiveData observer on change of any property in object
            setValue(getValue());

        }
    };


}

Then all you need to do is use this CustomMutableLiveData instead of MutableLiveData in your View Model

public class InfoViewModel extends AndroidViewModel {

    CustomMutableLiveData<User> user = new CustomMutableLiveData<>();
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So by doing this you can notify both view & LiveData observer with little change to existing code. Hope it helps

Solution 2:

When using MVVM and LiveData, you can re-bind the object to the layout so it will trigger all changes on the UI.

Given "user" is a MutableLiveData<User> in the ViewModel

ViewModel

class SampleViewModel : ViewModel() {
    val user = MutableLiveData<User>()

    fun onChange() {
        user.value.firstname = "New name"
        user.value = user.value // force postValue to notify Observers
        // can also use user.postValue()
    }
}

Activity/Fragment file:

viewModel = ViewModelProviders
            .of(this)
            .get(SampleViewModel::class.java)

// when viewModel.user changes, this observer get notified and re-bind
// the user model with the layout.
viewModel.user.observe(this, Observer {
    binding.user = it //<- re-binding user
})

Your layout file shouldn't change:

<data>
    <variable
        name="user"
        type="com.project.model.User" />
</data>

...

<TextView
        android:id="@+id/firstname"
        android:text="@{user.firstname}"
        />