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Android架构组件ViewModel可以从多个LiveData返回模型组成一个对象吗？

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我无法创建一个Android Architecuture组件ViewModel，它将多个LiveData模型组合成一个LiveData类，供我的Fragment观察 . 我想隐藏片段中的模型细节，并通过各个模型响应外部数据更改 .

问题是我需要ViewModel来观察模型更改，但ViewModel不是LifecycleOwner，因此无法观察 . 由于我不想将LiveData对象传递给UI，因此我陷入困境 .

这可能吗？我是否需要为我的模型放弃LiveData并采用不同的观察模式/工具？

Edit: 补充了伪代码 . 我的实际课程更加复杂和冗长 . 我希望我的意图是可以理解的 .

// OneDataModel.kt
class oneDataModel {
    val oneDataElement = ""
}

// AnotherDataModel.kt
class anotherDataModel {
    val anotherDataElement = 19
}

// OneDataRepository.kt
class OneDataRepository {
    val oneDataSet = MutableLiveData<MutableList<oneDataModel>>()

    private val dataListener = object: ChildEventListener {
        override fun onChildAdded(snapshot: DataSnapshot, p1: String?) {
            val newChild = snapshot.getValue(oneDataModel::class.java)
            if (newChild != null) {
                oneDataSet.value?.add(newChild)
            }
        }
    }

    init {
        oneDataSet.value = mutableListOf<oneDataModel>()
        OneNetworkDataTable.addListener(dataListener)
    }
}

// AnotherDataRepository.kt
class AnotherDataRepository {
    var anotherDataSet = MutableLiveData<MutableList<anotherDataModel>>()

    private val dataListener = object: ChildEventListener {
        override fun onChildAdded(snapshot: DataSnapshot, p1: String?) {
            val newChild = snapshot.getValue(anotherDataModel::class.java)
            if (newChild != null) {
                anotherDataSet.value?.add(newChild)
            }
        }
    }

    init {
        anotherDataSet.value = mutableListOf<anotherDataModel>()
        AnotherNetworkDataTable.addListener(dataListener)
    }
}

// ComposedViewModel.kt
class ComposedViewModel: ViewModel() {
    class ComposedItem {
        var dataName: String = ""   // From OneDataRepository items
        var dataValue: Int = -1     // From AnotherDataRepository items
    }
    var publishedDataSet = MutableLiveData<MutableList<ComposedItem>>()

    //***
    //*** WHAT GOES HERE? HOW DO I LISTEN TO EACH OF THE DATA REPOSITORIES AND BUILD UP COMPOSED
    //*** ITEMS FOR THE UI?
    //***
}

// MyFragment.kt
class MyFragment : Fragment() {
    private val composedViewModel: ComposedViewModel by lazy { ViewModelProviders.of(activity).get(ComposedViewModel::class.java) }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_feed, container, false)

        recyclerView.adapter = UIAdapter

        composedViewModel.publishedDataSet.observe(this, Observer {
            UIAdapter.notifyDataSetChanged()
        })

        return view
    }
}
android android-architecture-components architecture-components

2 回答

  • 1

    希望我的工作满足你的问题 .

    我之前制作了一个示例项目，现在将另一个假的liveata集成到这个视图模型中 . Difference of the file

    使用MediatorLiveData类将多数据源包装为一个 .

    FeedEntryListViewModel.java

    public class FeedEntryListViewModel extends ViewModel {

  //list all your live data here
  private LiveData<List<FeedEntry>> feedEntries = new MutableLiveData<>();
  private MutableLiveData<String> userId = new MutableLiveData<>();
  //show your composite model here
  private MediatorLiveData<CompositeModel> compositeModelLiveData;

  //list all your repository
  private FeedEntryRepository feedEntryDBRepository;

  /*
  The complete model to show the data
   */
  public static class CompositeModel {

    String userId = "SystemId";
    private List<FeedEntry> feedEntries = new ArrayList<>();


    public String getUserId() {
      return userId;
    }

    public void setUserId(String userId) {
      this.userId = userId;
    }

    public List<FeedEntry> getFeedEntries() {
      return feedEntries;
    }

    public void setFeedEntries(
        List<FeedEntry> feedEntries) {
      this.feedEntries = feedEntries;
    }


  }

  public FeedEntryListViewModel(
      FeedEntryRepository feedEntryDBRepository) {
    this.feedEntryDBRepository = feedEntryDBRepository;
    this.feedEntries = feedEntryDBRepository.getAll();
    this.compositeModelLiveData = new MediatorLiveData<>();
    this.compositeModelLiveData.addSource(feedEntries, data ->
    {
      CompositeModel compositeModel = compositeModelLiveData.getValue();
      compositeModel.setFeedEntries(data);
      compositeModelLiveData.postValue(compositeModel);
    });
    this.compositeModelLiveData.addSource(userId, data -> {
      CompositeModel compositeModel = compositeModelLiveData.getValue();
      compositeModel.setUserId(data);
      compositeModelLiveData.postValue(compositeModel);
    });
    //initialize the composite model to avoid NullPointerException
    this.compositeModelLiveData.postValue(new CompositeModel());
  }

  public void loadUserId(String userId) {
    this.userId.setValue(userId);
  }

  public LiveData<List<FeedEntry>> getFeedEntrys() {
    return feedEntryDBRepository.getAll();
  }

  public LiveData<CompositeModel> getCompositeEntrys() {
    return compositeModelLiveData;
  }

  public LiveData<List<FeedEntry>> insert(FeedEntry... feedEntries) {
    feedEntryDBRepository.insertAll(feedEntries);
    return feedEntryDBRepository.getAll();
  }

  public void delete(FeedEntry feedEntry) {
    feedEntryDBRepository.delete(feedEntry);
  }


  public int update(FeedEntry feedEntry) {
    return feedEntryDBRepository.update(feedEntry);
  }

}

    在Activity中，您仍然可以使用该语句获取复合

    viewModel.getCompositeEntrys().observe(this, entries -> {...});

    View Model Constructor添加实时数据并绑定到复合实时数据

    public FeedEntryListViewModel(
      FeedEntryRepository feedEntryDBRepository) {
    this.feedEntryDBRepository = feedEntryDBRepository;
    this.feedEntries = feedEntryDBRepository.getAll();
    this.compositeModelLiveData = new MediatorLiveData<>();
    this.compositeModelLiveData.addSource(feedEntries, data ->
    {
      CompositeModel compositeModel = compositeModelLiveData.getValue();
      compositeModel.setFeedEntries(data);
      compositeModelLiveData.postValue(compositeModel);
    });
    this.compositeModelLiveData.addSource(userId, data -> {
      CompositeModel compositeModel = compositeModelLiveData.getValue();
      compositeModel.setUserId(data);
      compositeModelLiveData.postValue(compositeModel);
    });
    //initialize the composite model to avoid NullPointerException
    this.compositeModelLiveData.postValue(new CompositeModel());
  }
    回复于
  • 0

    我建议采取不同的方法：

    • 使用反应流（RxJava）来表示您的模型

    • 使用架构组件中的 lifecycle-reactivestreams 将RxJava Observable转换为LiveData .

    通过使用RxJava，您可以轻松地将可观察对象合并在一起，并仅使用 LiveData 将该组合公开给视图 . 我建议仅使用 LiveData 将状态公开给视图（ Fragment 或 Activity ） .

    我写了一篇关于如何做到这一点的article . 你可能会发现它很有用 .

    回复于

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