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我是否应该将LiveData或Repository类的AsyncTask成员作为加载程序的替换

android-livedata android-jetpack android-architecture-components android

Cheok Yan Cheng · 技术社区 · 7 年前

LiveData / ViewModel 是一个很好的替代品 Loader .

基于 https://medium.com/google-developers/lifecycle-aware-data-loading-with-android-architecture-components-f95484159de4 ,

AsyncTask 是的成员 实时数据 .

public class JsonLiveData extends LiveData<List<String>> {

  public JsonLiveData(Context context) {

    loadData();
  }


  private void loadData() {
    new AsyncTask<Void,Void,List<String>>() {

    }.execute();
  }
}

但是,基于 presentation from Lyla Fujiwara :

我应该 异步任务 成员 Repository 上课?

1 回复 | 直到 7 年前

Knossos 7 年前

你应该避免跑你的 AsyncTask 在里面 LiveData . 实时数据 应该只关注数据的观察。不是改变数据的行为。

处理这种情况的最好方法是使用 ViewModel /存储库模式。

Activity / Fragment 从 视图模型 , 视图模型 观察 实时数据 从存储库。在存储库中进行更改,并将其推送到 实时数据 . 这些更改将传递给 活动/片段 (通过 视图模型 ).

在这种情况下,我会避免使用AsyncTask。AsyncTask的好处是,您可以在完成工作后在UI线程上获得结果。不过,在这种情况下,这是不必要的。LiveData会帮你的。

下面是一个(未经测试的)示例:

活动

public class MyActivity extends AppCompatActivity {

    private MyViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Set up your view model
        viewModel = ViewModelProviders.of(this).get(MyViewModel.class);

        // Observe the view model
        viewModel.getMyLiveData().observe(this, s -> {
            // You work with the data provided through the view model here.
            // You should only really be delivering UI updates at this point. Updating
            // a RecyclerView for example.
            Log.v("LIVEDATA", "The livedata changed: "+s);
        });

        // This will start the off-the-UI-thread work that we want to perform.
        MyRepository.getInstance().doSomeStuff();
    }
}

视图模型

public class MyViewModel extends AndroidViewModel {

    @NonNull
    private MyRepository repo = MyRepository.getInstance();

    @NonNull
    private LiveData<String> myLiveData;

    public MyViewModel(@NonNull Application application) {
        super(application);
        // The local live data needs to reference the repository live data
        myLiveData = repo.getMyLiveData();
    }

    @NonNull
    public LiveData<String> getMyLiveData() {
        return myLiveData;
    }
}

存储库

public class MyRepository {

    private static MyRepository instance;

    // Note the use of MutableLiveData, this allows changes to be made
    @NonNull
    private MutableLiveData<String> myLiveData = new MutableLiveData<>();

    public static MyRepository getInstance() {
        if(instance == null) {
            synchronized (MyRepository.class) {
                if(instance == null) {
                    instance = new MyRepository();
                }
            }
        }
        return instance;
    }

    // The getter upcasts to LiveData, this ensures that only the repository can cause a change
    @NonNull
    public LiveData<String> getMyLiveData() {
        return myLiveData;
    }

    // This method runs some work for 3 seconds. It then posts a status update to the live data.
    // This would effectively be the "doInBackground" method from AsyncTask.
    public void doSomeStuff() {
        new Thread(() -> {
            try {
                Thread.sleep(3000);
            } catch (InterruptedException ignored) {
            }

            myLiveData.postValue("Updated time: "+System.currentTimeMillis());
        }).start();
    }

}