Will the `onChanged` method trigger just as we cha

问题:

Will the onChanged method be called if we dont change the state of the activity or restart the activity? ( Even if the data changes ) . If it doesnt happen how shall i make it happen ?

onCreate() {
    viewModel.getHolidaysDatesFromServer(..).observe(.....this,new Observer<GetHolidaysDatesFromServer>) {
        onChanged(GetHolidaysDatesFromServer GetHolidaysDatesFromServer)
    }    
}

and my ViewModel class ...

public class CalendarLifeCycleOwner extends AndroidViewModel {
    Context context;
    MutableLiveData<GetHolidaysDatesFromServer> MutableLiveDataGetHolidays=new MutableLiveData<>();
    public CalendarLifeCycleOwner(@NonNull Application application) {
        super(application);
        this.context=application.getApplicationContext();
    }

    public MutableLiveData<GetHolidaysDatesFromServer> getHolidaysDatesFromServer(String upd_token,int product_id) {
        JustProductId justProductId=new JustProductId();
        justProductId.setProduct_id(product_id);
        UserListInterface userListInterface= UserListService.createService(UserListInterface.class, Utility.ACCEPT_HEADER_V4);
        Call<GetHolidaysDatesFromServer> getHolidaysDatesFromServerCall=userListInterface.GetProductHolidays(upd_token,justProductId);
        getHolidaysDatesFromServerCall.enqueue(new Callback<GetHolidaysDatesFromServer>() {
            @Override
            public void onResponse(Call<GetHolidaysDatesFromServer> call, Response<GetHolidaysDatesFromServer> response) {
                if (response.isSuccessful()) {
                    GetHolidaysDatesFromServer getHolidaysDatesFromServer=response.body();
                    MutableLiveDataGetHolidays.postValue(getHolidaysDatesFromServer);
                }
            }

            @Override
            public void onFailure(Call<GetHolidaysDatesFromServer> call, Throwable t) {
                ErrorObject errorObject=new ErrorObject(t);
                GetHolidaysDatesFromServer getHolidaysDatesFromServer=new GetHolidaysDatesFromServer();
                getHolidaysDatesFromServer.setErrorObject(errorObject);
                MutableLiveDataGetHolidays.setValue(getHolidaysDatesFromServer);

            }
        });
        return MutableLiveDataGetHolidays;
    }
}

But after i just change the data onChanged() is not getting called ...

回答1:

Google actually described that (or very familiar to that) kind of issue as an anti-pattern on the dev-summit. The recommended approach is to use switchMap from android.arch.lifecycle.Transformations class. You can see the documentation page for more details.

回答2:

Try using this and delete the global MutableLiveData variable

public MutableLiveData<GetHolidaysDatesFromServer> getHolidaysDatesFromServer(String upd_token,int product_id) {

       MutableLiveData<GetHolidaysDatesFromServer> MutableLiveDataGetHolidays=new MutableLiveData<>();

       //Your API call code goes here

       return MutableLiveDataGetHolidays;
 }