物品没有出现

Question

早上好， 我的源代码有问题，但是没有错误。  我正在使用Room数据库和viewModel创建一个包含文件夹项目的片段。我的问题是，当我添加新文件夹时，即使将其添加到数据库中，也不会在folderFragment中显示应用程序（即，无需按添加按钮）。  （我在其他活动中使用了相同的代码，并且可以使用，但这里没有结果）。

FolderFragment

public class AjouterDos_Fragment extends Fragment {
View view;
private DosViewModel dosViewModel;
private List<Dossier> listDos = new ArrayList<>();

public static final int ADD_DOS_REQUEST = 1;
private RecyclerView folder_recyclerView;
private FloatingActionButton btn_add_dos;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable 
  ViewGroup container, @Nullable Bundle savedInstanceState) {
    view = 
  inflater.inflate(R.layout.fragment_ajouter_dos_,container,false);

    btn_add_dos =  view.findViewById(R.id.btn_add_dos);

    btn_add_dos.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            showCustomDialog();

        }
    });

    folder_recyclerView = view.findViewById(R.id.folder_recyclerView);

    folder_recyclerView.setLayoutManager(new 
    LinearLayoutManager(getContext()));

    folder_recyclerView.setHasFixedSize(true);
   // folder_recyclerView.addItemDecoration(new 
    DividerItemDecoration(getContext(), DividerItemDecoration.VERTICAL));
    final DosAdapter adapter1 = new DosAdapter();

    folder_recyclerView.setAdapter(adapter1);


   dosViewModel = ViewModelProviders.of(this).get(DosViewModel.class);

    dosViewModel.insert(new Dossier(":3333333"));

    dosViewModel.getAllFolders().observe(this, new Observer<List<Dossier>> 
        () {
        @Override
        public void onChanged(@Nullable List<Dossier> dossiers) {
            //update RecyclerView
            adapter1.setDossiers(dossiers);

        }
    });
    return view ;
      }



     private void showCustomDialog() {
    final Dialog dialog = new Dialog(getContext());
    dialog.requestWindowFeature(Window.FEATURE_NO_TITLE); // before
    dialog.setContentView(R.layout.fragment_add_edit_dos);
    dialog.getWindow().setBackgroundDrawable(new 
    ColorDrawable(Color.TRANSPARENT));
    dialog.setCancelable(false);

    WindowManager.LayoutParams lp = new WindowManager.LayoutParams();
    lp.copyFrom(dialog.getWindow().getAttributes());
    lp.width = WindowManager.LayoutParams.MATCH_PARENT;
    lp.height = WindowManager.LayoutParams.WRAP_CONTENT;

    final Button add_dos = (Button) 
    dialog.findViewById(R.id.add_fold_btn);
    final Button back = (Button) dialog.findViewById(R.id.back_btn);

    final EditText titre = (EditText) dialog.findViewById(R.id.titre);
    back.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            dialog.dismiss();
            //toast.cancel();
        }
    });
    add_dos.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Dossier dos = new Dossier(titre.getText().toString());
            dosViewModel.insert(dos);
            dialog.dismiss();

        }
    });
    dialog.show();
    dialog.getWindow().setAttributes(lp);
}
 }

FolderViewModel

 public class DosViewModel extends AndroidViewModel {

private DosRepository dosRepository;

private LiveData<List<Dossier>> dossiers;

public DosViewModel(@NonNull Application application) {
    super(application);
    dosRepository = new DosRepository(application);
    dossiers = dosRepository.getAllFolders();
}

public void insert(Dossier dossier) { dosRepository.insert(dossier); }

public void update(Dossier dossier) {
    dosRepository.update(dossier);
}

public void delete(Dossier dossier) {
    dosRepository.delete(dossier);
}

public void deleteAllFolders() { dosRepository.deleteAllFolders(); }

public LiveData<List<Dossier>> getAllFolders() {
    return dossiers;
}
}

FolderRepository

public class DosRepository {

private DosDAO dosDAO;

private LiveData<List<Dossier>> dossiers;

public DosRepository(Application application) {
    DB_MJG database = DB_MJG.getInstance(application);

    dosDAO= database.dosDAO();
    dossiers = dosDAO.getAllFolders();
}

public void insert(Dossier dossier) {
    new InsertDosAsyncTask(dosDAO).execute(dossier);
}

public void update(Dossier dossier) {
    new UpdateDosAsyncTask(dosDAO).execute(dossier);
}

public void delete(Dossier dossier) {
    new DeleteDosAsyncTask(dosDAO).execute(dossier);
}

public void deleteAllFolders() {
    new DeleteAllDosAsyncTask(dosDAO).execute();
}

public LiveData<List<Dossier>> getAllFolders() {
    return dossiers;
}


private static class InsertDosAsyncTask extends AsyncTask<Dossier, Void, 
 Void> {
    private DosDAO dosDAO;

    private InsertDosAsyncTask(DosDAO dosDAO) {
        this.dosDAO =dosDAO;
    }

    @Override
    protected Void doInBackground(Dossier... dossiers) {
        dosDAO.insert(dossiers[0]);
        return null;
    }


}

private static class UpdateDosAsyncTask extends AsyncTask<Dossier, Void, 
 Void> {
    private DosDAO dosDAO;

    private UpdateDosAsyncTask(DosDAO dosDAO) {
        this.dosDAO = dosDAO;
    }

    @Override
    protected Void doInBackground(Dossier... dossiers) {
        dosDAO.update(dossiers[0]);
        return null;
    }
}

private static class DeleteDosAsyncTask extends AsyncTask<Dossier, Void, 
 Void> {
    private DosDAO dosDAO;

    private DeleteDosAsyncTask(DosDAO dosDAO) {
        this.dosDAO = dosDAO;
    }

    @Override
    protected Void doInBackground(Dossier... dossiers) {
        dosDAO.delete(dossiers[0]);
        return null;
    }
}

private static class DeleteAllDosAsyncTask extends AsyncTask<Void, Void, 
 Void> {
    private DosDAO dosDAO;

    private DeleteAllDosAsyncTask(DosDAO dosDAO) {
        this.dosDAO = dosDAO;
    }

    @Override
    protected Void doInBackground(Void... voids) {
        dosDAO.deleteAllFolders();
        return null;
     }
      }
  }

数据库

Database(entities = {Note.class,RDV.class, Dossier.class}, version = 2)
public abstract class DB_MJG  extends RoomDatabase {

private static DB_MJG instance;

public abstract NoteDAO noteDao();
public abstract DosDAO dosDAO(); 


public static  synchronized DB_MJG getInstance(Context context)
{
    if(instance==null){
        instance = Room.

   databaseBuilder(context.getApplicationContext(),DB_MJG.class,"MJGbd")
                .fallbackToDestructiveMigration()
                .addCallback(roomCallback)
                .build();
    }
    return instance;
}

private static RoomDatabase.Callback roomCallback = new 
  RoomDatabase.Callback() {
    @Override
    public void onCreate(@NonNull SupportSQLiteDatabase db) {
        super.onCreate(db);
       new PopulateDbAsyncTask(instance).execute();
    }
};
    private static class PopulateDbAsyncTask extends AsyncTask<Void, Void, 
  Void> 
  {
    private NoteDAO noteDAO;
    private DosDAO dosDAO;
    private PopulateDbAsyncTask(DB_MJG db) {
        noteDAO = db.noteDao();
        dosDAO = db.dosDAO();
    }

    @Override
    protected Void doInBackground(Void... voids) {
            noteDAO.insert(new Note("20/05/2019", "23:50", "Je t'aime my 
      liitle boy"));
            noteDAO.insert(new Note("21/05/2019", "23:50", "Je t'aime my 
      liitle girl"));
            dosDAO.insert(new Dossier(":3"));
        dosDAO.insert(new Dossier("Zmer"));
      return null;
    }
}

   }