Question

我正在从服务器中获取数据并保存在会议室数据库中，然后从会议室中将其显示在回收站视图中。数据已完美地保存在会议室数据库中并在回收站视图中显示。

问题：：当我从服务器数据库中删除某些数据时，其先前保存的旧副本仍然保留在房间中。

我想要的内容：我不想在回收器视图中显示从服务器删除的数据。因此，如何根据服务器的响应来更新会议室数据库。

这是我到目前为止所做的：

UserDao.java

@Dao
public interface UserDao {

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

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

User.java

@Entity(tableName = "Users")
public class User {

@NonNull
@PrimaryKey
private String id;

@ColumnInfo(name = "name")
@SerializedName("name")
@Expose
private String name;

@ColumnInfo(name = "age")
@SerializedName("age")
@Expose
private String age;

public User(String id,String name, String age) {
    this.id = id;
    this.name = name;
    this.age = age;
}

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getAge() {
    return age;
}

public void setAge(String age) {
    this.age = age;
}
}

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_SHORT).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;
}
}

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();
}

请让我知道如何获得期望的结果。任何帮助将不胜感激。

谢谢

Answer 1

使用getRoomUsers()从onResponse()中的存储库中获取已知用户的列表。

对于response.body()中的每个用户，检查其在已知用户列表中是否具有相应的列表项。删除该项目。

然后，已知用户列表将仅包含已从服务器删除的用户。因此，对于其余所有这些用户，您都可以将其从会议室数据库中删除。

以下代码片段显示了如何查找服务器当前未知的用户：

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

    List<User> list = response.body();
    List<User> previouslyKnownUsers = new ArrayList<>(userDb.userDao().getRoomUsers().getValue());

    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);

        User knownUser = null; 
        for(User previouslyKnownUser: previouslyKnownUsers){
            if(previouslyKnownUser.getId().equals(user.getId())){
                knownUser = previouslyKnownUser;
                break;
            }
        }
        if(knownUser != null){
            previouslyKnownUsers.remove(knownUser);
        }
    }

    for(User currentlyUnknownUser: previouslyKnownUsers){
        userDb.userDao().Delete(currentlyUnknownUser);
    }
}

为了使其工作，您必须在Delete(User user)

中添加方法UserDao.java

如何根据服务器响应更新会议室数据库

1 个答案: