LiveData - 第二次调用时没有获取片段中的数据

Question

我正在使用 LiveData 从服务器获取数据。在 onResume 方法中，每隔 5 秒调用相同的函数我只能在第一次 API 调用时获取数据。第二次没有触发观察者，无法获取片段中的数据。

这是我的片段：

    private int delay = 5 * 1000;
    private ViewModel mViewModel;
    private DetailsModel details = new DetailsModel();

    mViewModel = ViewModelProviders.of(this).get(ViewModel.class);
    mViewModel.getDetailsResponse("token", "ids");

    mViewModel.getData().observe(this, new Observer< DetailsModel >() {
                    @Override
                    public void onChanged(DetailsModel response) {

                        details = response;

                    }});
//getting data in every 5 seconds
@Override
    public void onResume() {
        super.onResume();

        liveHandler.postDelayed(runnable = new Runnable() {
            public void run() {
                mViewModel. getDetailsResponse("token", "ids");
                liveHandler.postDelayed(runnable, delay);
            }
        }, delay);
    }

ViewModel.java

 private MutableLiveData<DetailsModel> detailsResponse;
    private ProjectRepository repository  = new ProjectRepository();

    public void getDetailsResponse(String token, String ids) {
        detailsResponse = repository.getMapData("token", "ids");
    }

    public MutableLiveData<DetailsModel> getData() {
        return detailsResponse;
    }

ProjectRepository.java

public MutableLiveData<DetailsModel> getMapData(String token, String ids) {
        final MutableLiveData<DetailsModel> responseMutableLiveData = new MutableLiveData<>();

        Call<DetailsModel> call = service.getMapDetails(token, ids);
        call.enqueue(new Callback<DetailsModel>() {
            @Override
            public void onResponse(@NonNull Call<DetailsModel> call, @NonNull Response<DetailsModel> response) {
                responseMutableLiveData.postValue(response.body());
            }

            @Override
            public void onFailure(@NonNull Call<DetailsModel> call, @NonNull Throwable t) {
                t.printStackTrace();
            }
        });
        return responseMutableLiveData;
    }

Answer 1

无论何时调用 getDetailsResponse，都会创建一个新的 LiveData 对象，这就是问题所在，您应该在 ProjectRepository

中执行此操作

final MutableLiveData<DetailsModel> responseMutableLiveData = new MutableLiveData<>();

public MutableLiveData<DetailsModel> getMapData(String token, String ids) {
        Call<DetailsModel> call = service.getMapDetails(token, ids);
        call.enqueue(new Callback<DetailsModel>() {
            @Override
            public void onResponse(@NonNull Call<DetailsModel> call, @NonNull Response<DetailsModel> response) {
                responseMutableLiveData.postValue(response.body());
            }

            @Override
            public void onFailure(@NonNull Call<DetailsModel> call, @NonNull Throwable t) {
                t.printStackTrace();
            }
        });
        return responseMutableLiveData;
    }

在您的虚拟机中：

private MutableLiveData<DetailsModel> detailsResponse = null;
private ProjectRepository repository  = new ProjectRepository();

public void getDetailsResponse(String token, String ids) {
        if (detailsResponse == null) {
           detailsResponse = repository.getMapData("token", "ids");
        } else {
           // Just call it, you already assigned before
           repository.getMapData("token", "ids");
        }
}

public MutableLiveData<DetailsModel> getData() {
        return detailsResponse;
}

因此，基本上将对象创建移出函数本身。但是，您的 MVVM 实现的设计可以大大简化。我会敦促检查一些示例！

Answer 2

您正在使用 postDelayed() 两次，因此它不起作用。将您的 onResume() 代码更改为下面提到的。

@Override
public void onResume() {
    super.onResume();

    liveHandler.postDelayed(runnable = new Runnable() {
        public void run() {
            mViewModel.getDetailsResponse("token", "ids");
            liveHandler.post(runnable);
        }
    }, delay);
}

LiveData - 第二次调用时没有获取片段中的数据

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android

android-livedata

mutablelivedata