Observe One Livedata Into Other Livedata Observr

I have two LiveData: MutableLiveData -User could choose number by taping at '+' and '-' buttton. LiveData> - it's my data from RoomData base by call method getLesson

Solution 1:

First in your viewmodel define a liveData like this.

privateval dayOfWeekChangRequest = MutableLiveData<Int>()

and a method like this, when + , - clicked, call this method.

fundayOfWeekChanged(dayOfWeek: Int) {

    dayOfWeekChangRequest.value = dayOfWeek
}

now add a live data for lessonsOfThatDay

val lessonsForThatDay: LiveData<List<Lesson>> = Transformations
        .switchMap(dayOfWeekChangRequest) { day ->
            yourDataBaseRepository.getLessonsOfThatDay(day)
        }

with this transformation, every time you change your dayOfWeek, the lessonsForThatDay value will be changed.

at last in your activity observe it

viewModel.lessonsForThatDay.observe(viewLifecycleOwner, Observer { 
        lessons ->
        adapter.updateData(lessons)
        subjectsListTimetableRecyclerView.layoutManager = LinearLayoutManager(context)
        subjectsListTimetableRecyclerView.adapter = adapter
    })

Solution 2:

You can do viewModel = Dao.getLessonsForThatDay(number). This way, the viewmodel will listen to changes in Dao