如何从另一个liveData观察者调用liveData观察者

Question

I am working on livedata. I have two apis but one api is dependent on another api. Based on first api response i am calling another api using livedata observer. I am calling from inside observer is this a right approach or any other alternative

  mainViewModel.getListLiveData().observe(MainActivity.this, new Observer<List<Student>>() {
            @Override
            public void onChanged(@Nullable List<Student> list) {
                if(list.size() > 0){
                    mainViewModel.getStudentLiveData().observe(MainActivity.this, new Observer<Student>() {
                        @Override
                        public void onChanged(@Nullable Student student) {

                        }
                    });   
                }

            }
        });

Answer 1

Observe on the student LiveData exposed by the mainViewModel . In the viewmodel make student live data change with change in List LiveData using Transformations or using a MediatorLiveData

In your activity:

mainViewModel.getStudentLiveData().observe(this, new Observer<Student>() {
   student -> {}
});

In your viewmodel:

private MutableLiveData<List< Student>> studentListLiveData = new MutableLiveData(); // this will hold result of your first api call

private MutableLiveData<Student> studentLiveData = new MutableLiveData(); // this will hold result of your second api call


private void fetchData() {
    fetchStudentList(new Callback {
      result -> { 
           studentListLiveData.value = result; 
           fetchStudent(new Callback {
               result -> { studentLiveData.value = result; }
           });      
      }
    })
}

public LiveData<Student> getStudentLiveData() {
      return studentLiveData;
}