从 LiveData（房间数据库）填充 Spinner

Question

我在哪里

我正在尝试使用 Room 用数据库中的数据填充微调器。数据是一个术语列表，其中有与之关联的课程。

我想在创建新课程时使用微调器，以 select 与之关联的术语。

目前，微调器不显示默认选项，但如果您单击微调器，它会显示 select 来自的数据列表。在您 select 来自微调器的内容后，它不会显示您 select 编辑的内容。

这是我将数据加载到微调器适配器的代码：

        termsList = new ArrayList<>();
        termIdList = new ArrayList<>();
        mTermViewModel = new ViewModelProvider(this).get(TermViewModel.class);
        mTermViewModel.getAllTerms().observe(this, new Observer<List<TermEntity>>() {
            @Override
            public void onChanged(@Nullable final List<TermEntity> terms) {
                for (TermEntity term : terms) {
                    termsList.add(term.getTermName());
                    termIdList.add(term.getTermId());
                }
            }
        });

        ArrayAdapter<String> adapter = new ArrayAdapter<>(getContext(), android.R.layout.simple_spinner_item, termsList);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        mTermSpinner.setAdapter(adapter);
    }

这是TermDAO

@Dao
public interface TermDAO {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insert(TermEntity term);

    @Query("DELETE FROM terms")
    void deleteAllTerms();

    @Query("SELECT * FROM terms ORDER BY termId ASC")
    LiveData<List<TermEntity>> getAllTerms();

    @Query("SELECT * FROM terms WHERE termId = :termId")
    LiveData<List<TermEntity>> getTerm(int termId);

    @Query("SELECT termId FROM terms WHERE termName = :termName")
    LiveData<List<TermEntity>> getTermIdByTermName(String termName);
}

这是 TermViewModel

public class TermViewModel extends AndroidViewModel {
    private SchoolTrackerRepository mRepository;
    private LiveData<List<TermEntity>> mAllTerms;

    public TermViewModel(@NonNull Application application) {
        super(application);
        mRepository = new SchoolTrackerRepository(application);
        mAllTerms = mRepository.getAllTerms();
    }

    public LiveData<List<TermEntity>> getAllTerms() {
        return mAllTerms;
    }

    public void insert(TermEntity termEntity) {
        mRepository.insert(termEntity);
    }
}

我想在微调器中显示术语名称并使用相应的术语 ID 来执行查询。

我试过的

我尝试使用 Mutable LiveData 而不是 LiveData，但是当我尝试运行它时，我收到一条错误消息：

Error:Not sure how to convert a Cursor to this method's return type

我真的很茫然。感谢您的帮助。

已添加存储库

public class SchoolTrackerRepository {
    private TermDAO mTermDAO;
    private CourseDAO mCourseDAO;
    int termId;
    private LiveData<List<TermEntity>> mAllTerms;
    private LiveData<List<CourseEntity>> mAllCourses;
    private LiveData<List<CourseEntity>> mAssociatedCourses;

    public SchoolTrackerRepository(Application application) {
        SchoolTrackerDatabase db = SchoolTrackerDatabase.getDatabase(application);
        mTermDAO = db.termDAO();
        mCourseDAO = db.courseDAO();

        mAllTerms = mTermDAO.getAllTerms();
        mAllCourses = mCourseDAO.getAllCourses();
    }

    public LiveData<List<TermEntity>> getAllTerms() {
        return mAllTerms;
    }

    public LiveData<List<CourseEntity>> getAllCourses() {
        return mAllCourses;
    }

    public LiveData<List<CourseEntity>> getmAssociatedCourses(int termId) {
        return mAssociatedCourses;
    }

    public void insert(TermEntity termEntity) {
        new insertAsyncTask1(mTermDAO).execute(termEntity);
    }

    private static class insertAsyncTask1 extends AsyncTask<TermEntity, Void, Void> {
        private TermDAO mAsyncTaskDAO;

        insertAsyncTask1(TermDAO dao) {
            mAsyncTaskDAO = dao;
        }

        @Override
        protected Void doInBackground(final TermEntity... params) {
            mAsyncTaskDAO.insert(params[0]);
            return null;
        }
    }

    public void insert(CourseEntity courseEntity) {
        new insertAsyncTask2(mCourseDAO).execute(courseEntity);
    }

    private static class insertAsyncTask2 extends AsyncTask<CourseEntity, Void, Void> {
        private CourseDAO mAsyncCourseDAO;

        insertAsyncTask2(CourseDAO dao) {
            mAsyncCourseDAO = dao;
        }

        @Override
        protected Void doInBackground(final CourseEntity... params) {
            mAsyncCourseDAO.insert(params[0]);
            return null;
        }
    }
}

Answer 1

我猜你在更新 termsList 变量后缺少 notifyDataSetChanged。

试试这个：

ArrayAdapter<String> adapter = new ArrayAdapter<>(getContext(), android.R.layout.simple_spinner_item, termsList);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
mTermSpinner.setAdapter(adapter);

mTermViewModel = new ViewModelProvider(this).get(TermViewModel.class);
mTermViewModel.getAllTerms().observe(this, new Observer<List<TermEntity>>() {
    @Override
    public void onChanged(@Nullable final List<TermEntity> terms) {
        for (TermEntity term : terms) {
            termsList.add(term.getTermName());
            termIdList.add(term.getTermId());
        }

        //notifyDataSetChanged after update termsList variable here
        adapter.notifyDataSetChanged();
    }
});

从 LiveData（房间数据库）填充 Spinner

Populate Spinner from LiveData (Room Database)

android

dao

android-spinner

android-room

android-viewmodel