Question

我在哪里

我正在尝试使用Room从数据库中填充数据。数据是术语列表，其中包含与之相关的课程。

我想在创建新课程时使用微调框，以选择与之关联的术语。

当前，微调器不显示默认选项，但如果单击微调器，它将显示要选择的数据列表。从微调器中选择某项后，它不会显示您选择的内容。

这是我的代码，用于将数据加载到微调器的适配器中：

        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termId进行查询。

我尝试过的事情

我曾经尝试使用Mutable LiveData而不是LiveData，但是当我尝试运行它时，出现一个错误消息：

错误：不确定如何将游标转换为此方法的返回类型

我真的很茫然。感谢您的帮助。

添加的存储库

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

我想您在更新termsList变量后缺少了notifyDataSetChanged。

尝试一下：

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填充微调器（房间数据库）

1 个答案: