如何从存储库 class 为 MVVM 架构中的 Web 服务与 activity/fragment 通信

Question

我是 MVVM architecture 的新手，我只想知道如何在 repository class 和 UI (activity/fragment) class 之间进行通信。我遇到了正在执行此更新工作的实时数据same entities from both (remote and room database).

例如： 1）如果我有名为用户的实体。我可以使用如下实时数据保存和观察它：（来自 android 开发者网站）。

    public class UserRepository {
    private final Webservice webservice;
    private final UserDao userDao;
    private final Executor executor;

    @Inject
    public UserRepository(Webservice webservice, UserDao userDao, Executor executor) {
        this.webservice = webservice;
        this.userDao = userDao;
        this.executor = executor;
    }

    public LiveData<User> getUser(String userId) {
        refreshUser(userId);
        // Returns a LiveData object directly from the database.
        return userDao.load(userId);
    }

    private void refreshUser(final String userId) {
        // Runs in a background thread.
        executor.execute(() -> {
            // Check if user data was fetched recently.
            boolean userExists = userDao.hasUser(FRESH_TIMEOUT);
            if (!userExists) {
                // Refreshes the data.
                Response<User> response = webservice.getUser(userId).execute();

                // Check for errors here.

                // Updates the database. The LiveData object automatically
                // refreshes, so we don't need to do anything else here.
                userDao.save(response.body());
            }
        });
    }
}

2) 但是我们如何在不需要实时数据但我只想显示或隐藏进度对话框的其他 API 类似（登录）中执行此操作取决于网络成功或错误消息.

public void isVerifiedUser(int userId){
      executor.execute(() -> {
        // making request to server for verifying user

        Response<User> response = webservice.getVerifyUser(userId).execute();

          // how to update the UI like for success or error.
          //update the progress dialog also in UI class
        });
}

Answer 1

您需要制作 isVerifiedUser() return 一个 liveData，您可以在与 UI(activity/fragment).

相关的 viewModel 中观察到它

1.内部存储库：

public LiveData<State> isVerifiedUser(int userId){

    MutableLiveData<State> isVerified = new MutableLiveData();

    executor.execute(() -> {           
        Response<User> response = webservice.getVerifyUser(userId).execute();
        // Update state here.
        isVerified.postValue(valueHere)
    });

    return isVerified;
}

2。视图模型：

 public ViewModel(final Repository repository) {
        //observe userId and trigger isVerifiedUser when userId value is changed
        stateLiveData = Transformations.map(userId, new Function<>() {
            @Override
            public RepoMoviesResult apply(Integer userId) {
                return repository.isVerifiedUser(userId);
            }
        });
    }

3。 Activity:

viewModel.getStateLiveData ().observe(this, new Observer<>() {
    @Override
    public void onChanged(State state) {
         //do something here
    }
});

更多信息：

LiveData

ViewModel

Guide to app architecture MVVM

如何从存储库 class 为 MVVM 架构中的 Web 服务与 activity/fragment 通信

how to communicate to activity/fragment from repository class for web service in MVVM architecture

java

android-mvvm

android-room

android-livedata

android-architecture-components