如何从房间数据库中删除回收者视图项目

Question

我正在使用 MVVM 架构模型来创建应用程序。我在 MainActivity 中有回收器视图，单击回收器视图项目中的删除按钮时，它应该从房间数据库中删除。我知道可以在适配器类中删除项目，但作为我正在使用 MVVM 模型我想在 Repository 类中执行删除操作。

下面是我的代码：

UserDao.java

@Dao
public interface UserDao {

@Insert(onConflict = OnConflictStrategy.REPLACE)
void Insert(User... users);

@Query("SELECT * FROM Users")
LiveData<List<User>> getRoomUsers();

@Delete
void Delete(User... user);
}   

UserAdapter.java

public class UserAdapter extends 
RecyclerView.Adapter<UserAdapter.ViewHolder> {

List<User> userList;
Context context;

public UserAdapter(List<User> userList, Context context) {
    this.userList = userList;
    this.context = context;
}

@NonNull
@Override
public UserAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

    View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.user_row_layout,parent,false);

    ViewHolder viewHolder = new ViewHolder(v);

    return viewHolder;
}

@Override
public void onBindViewHolder(@NonNull UserAdapter.ViewHolder holder, int position) {

    final User users = userList.get(position);

    holder.row_name.setText(users.getName());
    holder.row_age.setText(users.getAge());

    holder.delete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {


        }
    });
}

@Override
public int getItemCount() {
    return userList.size();
}

public void setUserList(List<User> userList) {
    this.userList = userList;
    notifyDataSetChanged();
}

public class ViewHolder extends RecyclerView.ViewHolder {

    TextView row_name,row_age;
    ImageView delete;

    public ViewHolder(@NonNull View itemView) {
        super(itemView);

        row_name = itemView.findViewById(R.id.row_name);
        row_age = itemView.findViewById(R.id.row_age);
        delete = itemView.findViewById(R.id.delete);
      }
   }
}

UserRepository.java

public class UserRepository {

private Context context;
private UserDb userDb;
private LiveData<List<User>> listLiveData;

public UserRepository(Context context) {
    this.context = context;
    userDb = UserDb.getInstance(context);
    listLiveData = userDb.userDao().getRoomUsers();
}

public void getUserList(){

          Retrofit retrofit = RetrofitClient.getInstance();
          ApiService apiService = retrofit.create(ApiService.class);

          Call<List<User>> userList = apiService.getUser();

          userList.enqueue(new Callback<List<User>>() {
              @Override
              public void onResponse(Call<List<User>> call, final Response<List<User>> response) {

                  Completable.fromAction(new Action() {
                          @Override
                          public void run() throws Exception {

                              if(response.body() != null) {

                                  List<User> list = response.body();

                                  for (int i = 0; i < list.size(); i++) {

                                      String id = list.get(i).getId();
                                      String names = list.get(i).getName();
                                      String age = list.get(i).getAge();

                                          User user = new User(id,names,age);

                                          userDb.userDao().Insert(user);

                                   }
                                 }
                            }
                      }).subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(new CompletableObserver() {
                            @Override
                            public void onSubscribe(Disposable d) {

                            }

                            @Override
                            public void onComplete() {

                                Toast.makeText(context,"Data inserted",Toast.LENGTH_SHORT).show();
                            }

                            @Override
                            public void onError(Throwable e) {

                                Toast.makeText(context,e.getMessage(),Toast.LENGTH_LONG).show();
                            }
                        });


              }

              @Override
              public void onFailure(Call<List<User>> call, Throwable t) {
                  Toast.makeText(context,t.getMessage(),Toast.LENGTH_LONG).show();
              }
          });

}

public LiveData<List<User>> getRoomUsers(){

    return listLiveData;
  }
}

UserViewModel.java

public class UserViewModel extends AndroidViewModel {

private UserRepository repo;
private LiveData<List<User>> listLiveData;

public UserViewModel(@NonNull Application application) {
    super(application);

    repo = new UserRepository(application);
    listLiveData = repo.getRoomUsers();

}

public LiveData<List<User>> getListLiveData() {
    return listLiveData;
  }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

UserRepository userRepository;
RecyclerView recyclerView;
UserViewModel userModel;
List<User> userList;
UserAdapter adapter;
ProgressBar prg;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    prg = findViewById(R.id.prg);

    userRepository = new UserRepository(this);
    userModel = ViewModelProviders.of(this).get(UserViewModel.class);

    recyclerView = findViewById(R.id.recyclerView);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    userList = new ArrayList<>();

    adapter = new UserAdapter(userList,this);
    recyclerView.setAdapter(adapter);

    userModel.getListLiveData().observe(this, new Observer<List<User>>() {

        @Override
        public void onChanged(List<User> users) {

            prg.setVisibility(View.INVISIBLE);
            adapter.setUserList(users);
        }
    });

    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent i = new Intent(MainActivity.this,AddUser.class);
            startActivity(i);
        }
    });

    userRepository.getUserList();
 }

请告诉我如何实现删除操作。任何帮助将不胜感激。

谢谢

Answer 1

首先，在你的适配器类中初始化UserViewModel，就像你在MainActivity中所做的那样，然后调用delete函数。

holder.delete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
             userModel.deleteItem(users);  
        }
    });

在UserModel类中添加这个函数。

public void deleteItem(User user) = repo.deleteItem(user);

在UserRepository类中，调用Delete函数。

public void deleteItem(User user) {
        userDb.userDao().Delete(user);
 }

Answer 2

尝试使用实时数据观察数据库的变化，无论何时执行任何操作，添加或删除（在数据库中），在您的观察者中为回收站视图刷新该数据

为您的适配器设置点击监听器

public interface OnListInteractionListener {
        // TODO: Update argument type and name
        void onListInteraction(User user);
    }

在适配器类中

private final OnListInteractionListener mListener;

    public UserAdapter(List<User> users, OnListInteractionListener listener,Context context) {

        mListener = listener;
    }

并且在视图中绑定持有人

holder.delete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

mListener.onListInteraction(userList.get(position))
        }
    });

在您的活动/片段中实现该侦听器，然后您可以访问 Viewmodel 和 repo