Myujth

I am bit stuck at understanding the relation b/w using viewmodel and livedata. I hope that someone can explain it for me. I am new to Android Development.

For MVVM architecture it looks like this: you create model with your data, you access and change it in view model(in instances of LiveData). And observe it in views(activities/fragments).

MainViewModel extends ViewModel

 MutableLiveData<String> someStringObject = new MutableLiveData<>;

 private void someMethod
 someStringObject.setValue("For main thread");
 someStringObject.postValue("For back thread");
 

 public MutableLiveData<String> getSomeStringObject()
 return someStringObject;
 



FragmentA extends Fragment 

 @BindView(R.id.tv) //ButterKnife 
 TextView someTV;
 private MainViewModel mainViewModel;

 @Override
 public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
 Bundle savedInstanceState)
 //getting viewModel
 mainViewModel = ViewModelProviders.of(getActivity()).get(MainViewModel.class);
 //registering observer
 mainViewModel.getSomeStringObject.observe(this, value ->
 someTV.setText(value);
 );
 

This way you can react to changes of ViewModel in your View. Now if getSomeStringObject is changed in mainViewModel it will automatically change in FragmentA.

It's all well explained here. The ViewModel purpose is to manipulate the data so to provide the data needed to the view, like in any normal mvp pattern. LiveData instead is the (lifecycle aware) callback for the view model, so that any time the data set is updated (so the model has a potential change in its state), the execution flow is brought back to the model, so that the model can update itself, for instance manipulate the new data set before to provide it to the view. I hope it's clear