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,如果参数根据首选项发生更改,如何重新查询数据库。因为 View 模型是在 oncreate 方法中设置的,所以我们在 View 模型构造函数中调用 Dao 接口(interface)上的查询。
我试图在 onPreferenceChangeLitener 中重新创建 View 模型,但它不起作用。
我的主要 Activity 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);
}
}
View 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
最佳答案
您的方法存在一个问题,即您的 mMovies
是针对初始 movieType
(您在 MainActivityViewModel
中传递的类型)进行硬编码的。您应该修改您的 mMovies
用法,以便它可以对 movieType
更改作出 react 。
一个好的方法是创建一个额外的 LiveData
对象来监听 movieType
的变化,然后触发 mRepository.getMoviesList(movieType)
使用 Transformations.switchMap
调用新类型。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);
}
}
关于android - 在偏好更改监听器的基础上更改 android View 模型的查询参数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51797971/