仅第一次调用LiveData onChanged方法

我有一个简单的应用程序,可以轮询一个服务,在recyclerview中显示国家列表。在这里,每当国家/地区列表发生任何变化时,我都会使用LiveData更新recyclerview。问题是,LiveData的onChanged方法只有在第一次调用setValue时才被调用。但在此之后,如果数据有任何进一步的更改,则不会调用onChanged??

以下是我的代码以获取更多信息-

CountryListFragment

        //Setup observer
    Observer<List<CountryModel>> myObserver = new Observer<List<CountryModel>>() {
        @Override
        public void onChanged(@Nullable List<CountryModel> countryModels) {
            mCountryList = countryModels;
            //Update recyclerview
            myAdapter.updateRecyclerView(mCountryList);
        }
    };
    //Set Observer for Viewmodel
    countryViewModel.getmCountryList().observe(this,myObserver);

CountryViewModel

公共类CountryViewModel扩展了AndroidViewModel{ 私有MutableLiveData>McCountryList; 私人MyRefughtClient MyRefughtClient;

public CountryViewModel(@NonNull Application application) {
    super(application);
}

public void init(){
    mCountryList = new MutableLiveData<>();
    myRetrofitClient = new MyRetrofitClient();
    **mCountryList = myRetrofitClient.getCountryList();   //This works**
    pollCountryList();
}

//Create polling request for every 10 secs
private void pollCountryList(){
    final Handler mHandler = new Handler();

        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i=0; i<30;i++){
                    try {
                        Thread.sleep(10000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    //Call API on main thread
                    mHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            **myRetrofitClient.getCountryList();  //NOT CALLING ONCHANGED??**
                        }
                    });
                }

            }
        }).start();
}

public MutableLiveData<List<CountryModel>> getmCountryList() {
    return mCountryList;
}

MyReformationClient。getCountryList()

public MutableLiveData<List<CountryModel>> getCountryList(){
    final MutableLiveData<List<CountryModel>> lstResult = new MutableLiveData<>();
    MockServiceInterface serviceInterface = mRetrofit.create(MockServiceInterface.class);
    Call<List<CountryModel>> countryList = serviceInterface.getCountryList();
    countryList.enqueue(new Callback<List<CountryModel>>() {
        @Override
        public void onResponse(Call<List<CountryModel>> call, Response<List<CountryModel>> response) {
            if (response.isSuccessful()){
                List<CountryModel> lstResponse = response.body();
                lstResult.setValue(lstResponse);
            }else {
                System.out.print(response.errorBody());
            }
        }

        @Override
        public void onFailure(Call<List<CountryModel>> call, Throwable t) {
            t.printStackTrace();
        }
    });
    return lstResult;
}

谢谢

编辑:

一些补充意见- 在CountryViewModel中调用MutableLiveData实例(mCountryList)的setValue方法时,每次都会调用onChanged方法。

然而,对于MyRefughtClient,情况有所不同。第一次在MyRefundationClient中调用setValue。getCountryList(),它调用onChanged方法。但后来情况并非如此。