android - 根据preference change listener改变android view model的查询参数

Question

我在我的应用程序中使用架构组件。我使用了分页，但我有一个问题，如果参数根据偏好更改，如何重新查询数据库。因为视图模型是在 oncreate 方法中设置的，所以我们在视图模型构造函数中调用 Dao 接口上的查询。

我试图在 onPreferenceChangeLitener 中重新创建视图模型，但它不起作用。

我的主要活动是——

public class MainActivity extends AppCompatActivity implements SharedPreferences.OnSharedPreferenceChangeListener{

    private static final String TAG = MainActivity.class.getSimpleName();

    RecyclerView rvDisplayMovie;
    MovieAdapter mAdapter;

    MainActivityViewModel mViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        rvDisplayMovie = (RecyclerView) findViewById(R.id.rv_display_movies);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        rvDisplayMovie.setLayoutManager(linearLayoutManager);
        mAdapter = new MovieAdapter();

        rvDisplayMovie.setAdapter(mAdapter);

        MainViewModelFactory factory = InjectorUtils.provideMainViewModelFactory(this);

        mViewModel = ViewModelProviders.of(this, factory).get(MainActivityViewModel.class);

        mViewModel.getMovies().observe(this, new Observer<PagedList<MovieEntry>>() {
            @Override
            public void onChanged(@Nullable PagedList<MovieEntry> movieEntries) {
                Log.d(TAG,"Movie list changed"+movieEntries.size());
                mAdapter.submitList(movieEntries);
            }
        });

        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        sharedPreferences.registerOnSharedPreferenceChangeListener(this);

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        sharedPreferences.unregisterOnSharedPreferenceChangeListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main_settings,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_settings:
                Intent intent = new Intent(this, SettingsActivity.class);
                startActivity(intent);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String s) {
        mViewModel.triggerPrefsChenged(this);
    }
}

和视图模型是 -

public class MainActivityViewModel extends ViewModel {

    private static final String TAG = MainActivityViewModel.class.getSimpleName();

    private PopularMovieRepository mRepository;
    private LiveData<PagedList<MovieEntry>> mMovies;

    public MainActivityViewModel(PopularMovieRepository repository, int movieType){
        mRepository = repository;
        mMovies = mRepository.getMoviesList(movieType);
    }

    public  LiveData<PagedList<MovieEntry>> getMovies() {
        return mMovies;
    }

    public void triggerPrefsChenged(Context context){
        int movieType = PreferenceUtils.getMovieType(context);
        mRepository.initializeData(movieType);
    }
}

triggerPrefsChenged 方法下载新数据并将其插入数据库

标签： androidandroid-roomandroid-architecture-components

Answer 1

您的方法的一个问题是您mMovies对初始值movieType（您传入的那个）进行了硬编码MainActivityViewModel。您应该修改您的mMovies用法，以便它可以对movieType更改做出反应。

一个很好的方法是创建一个额外的LiveData对象来监听movieType变化，然后mRepository.getMoviesList(movieType)使用新类型触发调用Transformations.switchMap。因此，您的 ViewModel 可能如下所示：

public class MainActivityViewModel extends ViewModel {

    private static final String TAG = MainActivityViewModel.class.getSimpleName();
    private PopularMovieRepository mRepository;
    private final MutableLiveData<Integer> mMovieTypeLiveData = new MutableLiveData();
    private final LiveData<PagedList<MovieEntry>> mMovies;

    public MainActivityViewModel(PopularMovieRepository repository, int movieType){
        mRepository = repository;
        mMovies = Transformations.switchMap(movieTypeLive, (movieType) -> {
            return mRepository.getMoviesList(movieType);
        });
        //set the initial value
        mMovieTypeLiveData.setValue(movieType);
    }

    public LiveData<PagedList<MovieEntry>> getMovies() {
        return mMovies;
    }

    public void triggerPrefsChenged(Context context){
        int movieType = PreferenceUtils.getMovieType(context);
        //mRepository.initializeData(movieType);
        mMovieTypeLiveData.setValue(movieType);
    }
}