android livedata 进行顺序调用

Question

我正在使用 Retrofit，实时数据。我的项目有一种情况，我必须进行网络调用的顺序。如果任何一个失败，它应该 return 错误。

目前我有两个实时数据观察员来完成工作，这不是一个好方法所以我想知道更好的方法或示例代码来处理这种需求。

注意：我没有使用 Rxjava。

查看代码基本逻辑

    String id = "items/1233"; //ID which has to to be deleted
    if (isCustomizedItem) {
        viewModel.deleteEvent(id);
    } else {
        viewModel.createCustomItems();
        viewModel.deleteEvent(id);
    }

实时数据观察者

    viewModel.getItemDeleted().observe(this, serverResponse -> {
        if (serverResponse.status == Status.SUCCESS) {
            Timber.i("Successfully deleted");
        }
    });

    viewModel.itemCreated().observe(this, serverResponse -> {
        if (serverResponse.status == Status.SUCCESS) {
            Timber.i("new items added");
            //Again call delete for specific item
            viewModel.deleteEvent(id);
        }
    });

查看模型代码

    createItems = Transformations.switchMap(eventData, (data) -> {
        if (canCreateItems(data)) {
            return AbsentLiveData.create();
        } else {
            return eventItemRepository.createItems();
        }
    });

    deleteItem = Transformations.switchMap(deleteItem, (item) -> {
        if (!isValidItem(item)) {
            return AbsentLiveData.create();
        } else {
            return eventItemRepository.deleteItem(item);
        }
    });

回购代码。

public LiveData<Resource<List<Items>>>  createItems() {
    return new NetworkBoundResource<List<Items>> (executors) {
        @NonNull
        @Override
        protected LiveData<ApiResponse<List<Items>>> createCall() {
            return services.createItems();
        }
    }.asLiveData();
}
public LiveData<Resource<EmptyResponse>>  deleteItem(String id) {
    return new NetworkBoundResource<EmptyResponse> (executors) {
        @NonNull
        @Override
        protected LiveData<ApiResponse<EmptyResponse>> createCall() {
            return services.deleteItem(id);
        }
    }.asLiveData();
}

服务接口。

@GET(Constants.API_PATH+"/createitems/")
LiveData<ApiResponse<List<Items>>> createItems();

@GET(Constants.API_PATH+"/delete/{id}")
LiveData<ApiResponse<EmptyResponse>> deleteItem(@Path("id") String id);

我想同时调用createItems 和deleteItem。我怎样才能做到这一点？

Answer 1

终于写出解决方案了。我使用 Mediatorlivedata 观察 viewmodel 上的 livedata 变化。

Method which is responsible for both network call

public LiveData<Resource<EmptyResponse>> updateEvent(RequestCustomEvent request) {
    return new UpdateItineraryRequests<EmptyResponse>(request).asLiveData();
}

和一个 class，它将观察视图模型上的实时数据变化。

   private class UpdateItineraryRequests<RequestType> {
    private final MediatorLiveData<Resource<RequestType>> result = new MediatorLiveData<>();

    UpdateItineraryRequests(RequestCustomEvent request) {
        startExecution(request);
    }

    void startExecution(RequestCustomEvent request) {
        //First check the its custom or not if its custom then directly change.
        if (request.isCustom()) {
            LiveData<Resource<EmptyResponse>> observable = repo.deleteItem(request.getEventID());
            result.addSource(observable, response -> {
                result.removeSource(observable);
                if (response.status == Status.SUCCESS) {
                    result.setValue(Resource.success(null));
                } else {
                    result.setValue(Resource.error("unable to delete", null));
                }

            });
        } else {
            LiveData<Resource<List<Items>>> itemsObservable = repo.createItems(request.getDataToChange());
            result.addSource(itemsObservable, response -> {
                result.removeSource(itemsObservable);
                LiveData<Resource<EmptyResponse>> observable = repo.deleteItem(request.getEventID());
                result.addSource(observable, response -> {
                    result.removeSource(observable);
                    if (response.status == Status.SUCCESS) {
                        //Do rest of network calls
                    }

                }
            });
        }

    }

    LiveData<Resource<RequestType>> asLiveData() {
        return result;
    }

}

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