tom*_*mas 4 android android-livedata android-architecture-components android-paging
我正在为我的数据使用新的分页库.创建ViewModel并首次初始化实时数据时,一切正常.问题是,当我点击菜单项并希望用不同的数据集更新时,我无法更新我的实时数据的值.然后我的片段中的onChanged方法不会被调用.我已经阅读了有关MutableLiveData和setValue和postValue等可以更新实时数据的方法,但在我的情况下,我使用的是LivePagedListProvider并且无法从数据库返回MutableLiveData.
道:
@Query("SELECT * FROM teams ORDER BY name ASC")
LivePagedListProvider<Integer, Team> getAllTeams();
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分段:
mTeamViewModel.mTeamsList.observe(this, new Observer<PagedList<Team>>() {
@Override
public void onChanged(@Nullable PagedList<Team> teams) {
mTeamAdapter.setList(teams);
}
});
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视图模型:
public LiveData<PagedList<Team>> mTeamsList;
@Inject
DatabaseManager mDatabaseManager;
void setTeamViewModel(final DatabaseManager databaseManager) {
mDatabaseManager = databaseManager;
mTeamsList = mDatabaseManager.getAllTeams().create(
0,
new PagedList.Config.Builder()
.setPageSize(50)
.setPrefetchDistance(50)
.setEnablePlaceholders(true)
.build());
}
boolean onOptionsItemSelected(final MenuItem item) {
switch (item.getItemId()) {
case R.id.action_favorite:
mTeamsList = mDatabaseManager.getFavoriteTeams().create(
0,
new PagedList.Config.Builder()
.setPageSize(50)
.setPrefetchDistance(50)
.build());
return true;
default: return false;
}
}
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最后我在3天的斗争后找到了解决方案,
要更新LiveData的值,我们可以在ViewModel中使用MediatorLiveData,如下所示 -
public LiveData<PagedList<RecipeListPojo>> liveData;
private MediatorLiveData<PagedList<RecipeListPojo>> mediatorLiveData;
public RecipeListViewModel(@NonNull Application application) {
super(application);
mediatorLiveData=new MediatorLiveData<>();
}
public MediatorLiveData<PagedList<RecipeListPojo>> init(RecipeDao recipeDao,RecipeFrom recipeFrom,String orderBy) {
liveData = new LivePagedListBuilder(recipeDao.getAllRecipesList(simpleSQLiteQuery), 6).build();
mediatorLiveData.addSource(liveData, new Observer<PagedList<RecipeListPojo>>() {
@Override
public void onChanged(@Nullable PagedList<RecipeListPojo> recipeListPojos) {
mediatorLiveData.setValue(recipeListPojos);
}
});
return mediatorLiveData;
}
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有关MediatorLiveData的更多详细信息,请参见此处
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