Question

viewpager中的片段在销毁并重新创建时不会更新UI。（当您滑回到该片段时，视图不会更新）

仅在第一次创建片段时更新视图。这就是我在项目中实现MVVM的方式。

活动分类：

protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.activity_main); 
Fragment frag = new NewLocationFrag();
Bundle fragBundle = new Bundle();
pagerAdapter.addFrag(frag);
}

类片段：

public class NewLocationFrag extends Fragment {
private WeatherDataViewModel mWeatherDataViewMode;
public void onCreate(@Nullable Bundle savedInstanceState)       {
    mWeatherDataViewMode = ViewModelProviders.of(this).get(WeatherDataViewModel.class);
    mWeatherDataViewMode.init(mLoc,getActivity());
    mWeatherDataViewMode.getmForecastDataMutable().observe(this, new Observer<ArrayList<ForecastData>>() {
        @Override
        public void onChanged(@Nullable ArrayList<ForecastData> forecastData) {
            Timber.d("mvvm");
            // update UI like setText...
        }
    });
}

class WeatherDataViewModel.class

public class WeatherDataViewModel extends ViewModel {
private MutableLiveData<Map<String, String>> mWeatherDataMapMutable;// = new MutableLiveData<>();
private MutableLiveData<ArrayList<ForecastData>> mForecastDataMutable;// = new MutableLiveData<>();
private WeatherDataRepository mRepo;
private Context mCtx;

public void init(@NonNull String mLoc, @NonNull Context ctx) {
    mCtx = ctx;
    mRepo = WeatherDataRepository.getInstance(mCtx);
    mRepo.setWeatherData(mLoc);

    mForecastDataMutable = mRepo.getForecastDataMutable();
    mWeatherDataMapMutable = mRepo.getWeatherDataMap();
}

public MutableLiveData<Map<String, String>> getmWeatherDataMapMutable() {
    Timber.d("mvvm");

    return mRepo.getWeatherDataMap();
}

public MutableLiveData<ArrayList<ForecastData>> getmForecastDataMutable() {
    Timber.d("mvvm");
    return mRepo.getForecastDataMutable();
}
}

存储库

public class WeatherDataRepository {
private MutableLiveData<Map<String,String>> weatherDataMapMutable = new MutableLiveData<Map<String,String>>();
private MutableLiveData<ArrayList<ForecastData>> forecastDataMutable = new MutableLiveData<ArrayList<ForecastData>>();

private static WeatherDataRepository instance;
private Context mCtx;

public WeatherDataRepository(Context ctx){
    mCtx = ctx;
}

public static WeatherDataRepository getInstance(Context ctx){
    if(instance == null){
        instance = new WeatherDataRepository(ctx);
    }
    return instance;
}


// Pretend to get data from a webservice or online source
public void setWeatherData(@NonNull String mLoc){
    RetrofitQuery query = new RetrofitQuery(mCtx);
    //workaround
    Call<predictWeatherData> call2= query.GetWeatherData(mLoc);
    Map<String,String> weatherDataMap;
    call2.enqueue(new Callback<predictWeatherData>(){
        @Override
        public void onResponse(@NonNull Call<predictWeatherData> call, @NonNull Response<predictWeatherData> response) {
            if(response.isSuccessful()){
                predictWeatherData weatherStatus = Objects.requireNonNull(response.body());

                weatherDataMapMutable = new MutableLiveData<>();
                weatherDataMapMutable.setValue(Objects.requireNonNull(CreateWeatherDataMap.
                        createWeatherData(weatherStatus)));
                forecastDataMutable = new MutableLiveData<>();
                forecastDataMutable.setValue(Objects.requireNonNull(CreateWeatherDataMap.
                        createOneWeekWeatherData(weatherStatus)));

                }
            }


        @Override
        public void onFailure(Call<predictWeatherData> call, Throwable t) {
            if(t instanceof IOException){
                Timber.d("Retrofit: IOException ");
            }
            Timber.d(" Retrofit: query failed: parsing error");
        }
    });

}

public MutableLiveData<Map<String,String>> getWeatherDataMap(){

        Timber.d("mvvm");
        return weatherDataMapMutable;
}

public MutableLiveData<ArrayList<ForecastData>> getForecastDataMutable(){
        Timber.d("mvvm");

    return forecastDataMutable;
}
}

我最初是用MVC架构实现的，并且可以正常工作。不知道这种新方法有什么问题。

MVVM实现不会更新ViewPager中的片段视图

0 个答案: