调用 MutableLiveData Web service agine 来更新列表

Question

我在项目中使用 MVVM 结构。 我有一个主要片段，列表观察到一个 Web 服务，如您在代码中看到的那样

片段：

mViewModel.getHomePageList().observe(this, homeDataWrapper -> {
if (homeDataWrapper!=null) {
if (homeDataWrapper.isStatus()) {
binding.homeProgressBar.setVisibility(View.INVISIBLE);
ToastUtil.showTosat(homeDataWrapper.getData().getMessage(), getContext());
Log.d(TAG, "onChanged: ");
}
}
});

查看型号：

ublic class HomePageViewModel extends AndroidViewModel {
private MutableLiveData<DataWrapper<Home>> data;
public ObservableInt loading;
private HomeRepository homeRepository;
private HomePageAdapter adapter;
public HomePageViewModel(@NonNull Application application) {
super(application);
}
public void init() {
adapter = new HomePageAdapter(R.layout.main_page_list, this);
homeRepository = new HomeRepository();
if (this.data != null) {
// ViewModel is created per Fragment so
// we know the userId won't change
return;
}
data = homeRepository.getHomeScreen();
}

public HomePageAdapter getAdapter() {
return adapter;
}
public void onItemClick(Integer index) {
}
public void onSerachClicked(View view) {
Navigation.findNavController(view).navigate(R.id.action_homePageFragment_to_searchActivity);
}

public MutableLiveData<DataWrapper<Home>> getHomePageList() {
return this.data;
}
}

首页存储库 ：

public MutableLiveData<DataWrapper<Home>> getHomeScreen() {
final MutableLiveData<DataWrapper<Home>> homeMutableLiveData = new MutableLiveData<>();
final DataWrapper<Home> dataWrapper = new DataWrapper<>();
RetrofitInstance.getApiService().getHome().enqueue(new Callback<Home>() {
@Override
public void onResponse(@NotNull Call<Home> call, @NotNull Response<Home> response) {
Log.d("", "onResponse: " + response);
if (response.code() == 200) {
dataWrapper.setData(response.body());
dataWrapper.setStatus(true);
homeMutableLiveData.postValue(dataWrapper);
}
}
@Override
public void onFailure(Call<Home> call, Throwable t) {
Log.d("", "onResponse: " + t);
dataWrapper.setApiException((Exception) t);
dataWrapper.setStatus(false);
homeMutableLiveData.postValue(dataWrapper);
}
});
return homeMutableLiveData;
}

我想添加滑动刷新布局以更新主列表。 再次调用 Web 服务并更新列表的正确方法是什么？ 谁能帮我？

Answer 1

你可以调用getHomeScreenRepository 类再次触发从服务器拉取数据，拉取请求完成后，将使用MutableLiveData通知观察者。

但这是您的问题，每次调用getHomeScreen时都会创建一个新的MutableLiveData对象。因此，第一个不会收到通知，列表也不会更新！

要解决此问题，您必须在其他地方初始化MutableLiveData，以便每次调用getHomeScreen时都不会再次创建它。

我建议你把你的HomeRepository类做成一个单例类，并在构造函数中初始化MutableLiveData对象，然后你可以在从服务器获得新数据后使用此对象将数据发布给观察者。

public class HomeRepository {
private static HomeRepository instance;
private MutableLiveData<DataWrapper<Home>> homeMutableLiveData;
public static HomeRepository getInstance() {
if(instance == null) instance = new HomeRepository();
return instance;
}
private HomeRepository() {
homeMutableLiveData = new MutableLiveData<>();
}
public MutableLiveData<DataWrapper<Home>> getHomeScreen() {
final DataWrapper<Home> dataWrapper = new DataWrapper<>();
RetrofitInstance.getApiService().getHome().enqueue(new Callback<Home>() {
@Override
public void onResponse(@NotNull Call<Home> call, @NotNull Response<Home> response) {
Log.d("", "onResponse: " + response);
if (response.code() == 200) {
dataWrapper.setData(response.body());
dataWrapper.setStatus(true);
homeMutableLiveData.postValue(dataWrapper);
}
}
@Override
public void onFailure(Call<Home> call, Throwable t) {
Log.d("", "onResponse: " + t);
dataWrapper.setApiException((Exception) t);
dataWrapper.setStatus(false);
homeMutableLiveData.postValue(dataWrapper);
}
});
return homeMutableLiveData;
}
}

Answer 2

Inside onReferesh片段的侦听器

swifeRefresh.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
mViewModel.getHomeScreenDetail();
}
});

在视图模型中创建 getHomeScreenDetail 方法

public void getHomeScreenDetail(){
data = homeRepository.getHomeScreen();
}