AAC: How return result (handle click) from ViewModel to activity? - mvvm

Question

I want to use in my project Android Architecture Components (AAC).
Nice.
Here my activity:
import androidx.appcompat.app.AppCompatActivity;
public class TradersActivity extends AppCompatActivity {
private TradersViewModel tradersViewModel;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tradersViewModel = ViewModelProviders.of(this).get(TradersViewModel.class);
tradersViewModel.getIsEnableSwipeProgress().observe(this, new Observer<Boolean>() {
#Override
public void onChanged(Boolean isEnable) {
// do some work with UI
}
});
}
// button click
public void onClickViewJson(Trader trader) {
tradersViewModel.doClickJsonView(trader);
}
}
Here my ViewModel
public class TradersViewModel extends ViewModel {
private MutableLiveData<Boolean> isEnableSwipeProgress = new MutableLiveData<>();
public void doClickJsonView(Trader trader) {
// DO_SOME_COMPLEX_BUSINESS_LOGIC
}
public MutableLiveData<Boolean> getIsEnableSwipeProgress() {
return isEnableSwipeProgress;
}
}
In the screen I has button. And when click this button I call activity's method - onClickViewJson(Trader trader) .
This method call tradersViewModel.doClickJsonView(trader);
In the viewModel this method do some complex business logic.
After method finish it work I need to return result (json) to the my activity.
How I can do this?

Answer 1

Remember that in MVVM, ViewModels have not idea about your view.
Your ViewModel should expose variables so your views can observe and react over them.
private MutableLiveData<Boolean> isEnableSwipeProgress = new MutableLiveData<>();
private MutableLiveData<JSONDto> jsonLiveData = new MutableLiveData<>();
public void doClickJsonView(Trader trader) {
// DO_SOME_COMPLEX_BUSINESS_LOGIC
jsonLiveData.postValue(/* the json you obtain after your logic finish */ )
}
public MutableLiveData<Boolean> getIsEnableSwipeProgress() {
return isEnableSwipeProgress;
}
public LiveData<JSONDto> getJsonDto() {
return this.jsonLiveData;
}
And in your view, you react over your jsonDto changes:
tradersViewModel.getJsonDto().observe(this, new Observer<JSONDto>() {
#Override
public void onChanged(JSONDto json) {
if (json != null) {
// Do what you need here.
}
}
});