How to observe LiveData created by Service from UI/MainActivity/Fragments?

Question

I have a service that updates data every now and then. I currently use sharedPreferences to store the data and use LocalBroadcast to communicate between the service and UI.

I would like to improve this to use MutableLiveData, something like so.

class MyService : Service() {
    private var mMyServiceCreatedData = MutableLiveData<String>()
    private var mData = ""

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        ....
        mData = someData
        mMyServiceCreatedData.postValue(mData)
    }
}

I understand there's viewModel but in this case it's the service which generates the data and not a viewModel so I don't know how it works for Service. Is it possible to observe data created from a Service in UI/MainActivity/Fragments?

Answer 1

There are many different approaches to this, so I won't go into too much detail; Stack Overflow is not built around that.

LiveData is just a value holder. It is when "observers" come to "observe" your events that you start having to think about Lifecycle.

If you don't like the LocalBroadcast mode, then you could:

1. Service stores the value in a repository instead of emitting/posting the value.
2. Repository emits a flow or exposes LiveData (I don't like liveData in repos but that's fine).
3. ViewModel (and UI/Fragment/Act) will eventually subscribe to this Repository (same instance, I assume you have Dependency Injection or pass your references anyway you want), when it's in scope.

This decouples all the pieces and allows them to run independently of each other.

As a last resort, you could always bind your service to your activity, but that's -I believe- a different use-case than this.

Answer 2

Finally I fixed it.

1. Create MyApp class which extends Application

2. Create instance of MyApp

   private static MyApp myApp; public static MyApp getInstance() { return myApp; }

3. Access MyApp from your service/fragment/anywhere you want.

4. Create instance of your model class in MyApp.

   public ViewModel model; @Override public void onCreate() { super.onCreate(); model = new ViewModelProvider(this).get(ViewModel.class);

5. To access your model

 MyApp.getInstance().model.doYourWork(); 

6. Using this you can update your model and update ui.