“onChanged”方法会在我们更改数据时触发吗?即使我们不改变活动状态

Question

如果我们不更改活动的状态或重新启动活动，是否会调用onChanged方法？(即使数据发生变化(。如果它没有发生，我该如何让它发生？

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

和我的视图模型类...

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;
    }
}

但是在我只是更改数据后onChanged()没有被调用......

Answer 1

谷歌实际上将这种(或非常熟悉的(问题描述为开发峰会上的反模式。建议的方法是使用类android.arch.lifecycle.Transformations switchMap。有关更多详细信息，请参阅文档页面。

Answer 2

尝试使用它并删除全局 MutableLiveData 变量

public MutableLiveData<GetHolidaysDatesFromServer> getHolidaysDatesFromServer(String upd_token,int product_id) {
       MutableLiveData<GetHolidaysDatesFromServer> MutableLiveDataGetHolidays=new MutableLiveData<>();
       //Your API call code goes here
       return MutableLiveDataGetHolidays;
 }