如何从 MVVM 架构中的 Web 服务的存储库类与活动/片段进行通信

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。我遇到了实时数据，这些数据正在执行更新same entities from both (remote and room database) 的工作。

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并观察它：（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 中做到这一点（登录）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

您需要让 isVerifiedUser() 返回一个 liveData，您可以在与该 UI（活动/片段）相关的 viewModel 中观察它。

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.活动：

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