טרנספורמציה של מקורות נתונים

pager.flow // Type is Flow<PagingData<User>>.
  // Map the outer stream so that the transformations are applied to
  // each new generation of PagingData.
  .map { pagingData ->
    // Transformations in this block are applied to the items
    // in the paged data.
}

PagingRx.getFlowable(pager) // Type is Flowable<PagingData<User>>.
  // Map the outer stream so that the transformations are applied to
  // each new generation of PagingData.
  .map(pagingData -> {
    // Transformations in this block are applied to the items
    // in the paged data.
  });

// Map the outer stream so that the transformations are applied to
// each new generation of PagingData.
Transformations.map(
  // Type is LiveData<PagingData<User>>.
  PagingLiveData.getLiveData(pager),
  pagingData -> {
    // Transformations in this block are applied to the items
    // in the paged data.
  });

pager.flow // Type is Flow<PagingData<User>>.
  .map { pagingData ->
    pagingData.map { user -> UiModel(user) }
  }

// Type is Flowable<PagingData<User>>.
PagingRx.getFlowable(pager)
  .map(pagingData ->
    pagingData.map(UiModel.UserModel::new)
  )

Transformations.map(
  // Type is LiveData<PagingData<User>>.
  PagingLiveData.getLiveData(pager),
  pagingData ->
    pagingData.map(UiModel.UserModel::new)
)

private val queryFlow = MutableStateFlow("")

fun onQueryChanged(query: String) {
  queryFlow.value = query
}

private BehaviorSubject<String> querySubject = BehaviorSubject.create("");

public void onQueryChanged(String query) {
  queryFlow.onNext(query)
}

private MutableLiveData<String> queryLiveData = new MutableLiveData("");

public void onQueryChanged(String query) {
  queryFlow.setValue(query)
}

val querySearchResults = queryFlow.flatMapLatest { query ->
  // The database query returns a Flow which is output through
  // querySearchResults
  userDatabase.searchBy(query)
}

Observable<User> querySearchResults =
  querySubject.switchMap(query -> userDatabase.searchBy(query));

LiveData<User> querySearchResults = Transformations.switchMap(
  queryLiveData,
  query -> userDatabase.searchBy(query)
);

pager.flow // Type is Flow<PagingData<User>>.
  .map { pagingData ->
    pagingData.filter { user -> !user.hiddenFromUi }
  }

// Type is Flowable<PagingData<User>>.
PagingRx.getFlowable(pager)
  .map(pagingData ->
    pagingData.filter(user -> !user.isHiddenFromUi())
  )
}

Transformations.map(
  // Type is LiveData<PagingData<User>>.
  PagingLiveData.getLiveData(pager),
  pagingData ->
    pagingData.filter(user -> !user.isHiddenFromUi())
)

sealed class UiModel {
  class UserModel(val id: String, val label: String) : UiModel() {
    constructor(user: User) : this(user.id, user.label)
  }

  class SeparatorModel(val description: String) : UiModel()
}

class UiModel {
  private UiModel() {}

  static class UserModel extends UiModel {
    @NonNull
    private String mId;
    @NonNull
    private String mLabel;

    UserModel(@NonNull String id, @NonNull String label) {
      mId = id;
      mLabel = label;
    }

    UserModel(@NonNull User user) {
      mId = user.id;
      mLabel = user.label;
    }

    @NonNull
    public String getId() {
      return mId;
    }

    @NonNull
    public String getLabel() {
      return mLabel;
      }
    }

    static class SeparatorModel extends UiModel {
    @NonNull
    private String mDescription;

    SeparatorModel(@NonNull String description) {
      mDescription = description;
    }

    @NonNull
    public String getDescription() {
      return mDescription;
    }
  }
}

class UiModel {
  private UiModel() {}

  static class UserModel extends UiModel {
    @NonNull
    private String mId;
    @NonNull
    private String mLabel;

    UserModel(@NonNull String id, @NonNull String label) {
      mId = id;
      mLabel = label;
    }

    UserModel(@NonNull User user) {
      mId = user.id;
      mLabel = user.label;
    }

    @NonNull
    public String getId() {
      return mId;
    }

    @NonNull
    public String getLabel() {
      return mLabel;
      }
    }

    static class SeparatorModel extends UiModel {
    @NonNull
    private String mDescription;

    SeparatorModel(@NonNull String description) {
      mDescription = description;
    }

    @NonNull
    public String getDescription() {
      return mDescription;
    }
  }
}

pager.flow.map { pagingData: PagingData<User> ->
  // Map outer stream, so you can perform transformations on
  // each paging generation.
  pagingData
  .map { user ->
    // Convert items in stream to UiModel.UserModel.
    UiModel.UserModel(user)
  }
  .insertSeparators<UiModel.UserModel, UiModel> { before, after ->
    when {
      before == null -> UiModel.SeparatorModel("HEADER")
      after == null -> UiModel.SeparatorModel("FOOTER")
      shouldSeparate(before, after) -> UiModel.SeparatorModel(
        "BETWEEN ITEMS $before AND $after"
      )
      // Return null to avoid adding a separator between two items.
      else -> null
    }
  }
}

// Map outer stream, so you can perform transformations on each
// paging generation.
PagingRx.getFlowable(pager).map(pagingData -> {
  // First convert items in stream to UiModel.UserModel.
  PagingData<UiModel> uiModelPagingData = pagingData.map(
    UiModel.UserModel::new);

  // Insert UiModel.SeparatorModel, which produces PagingData of
  // generic type UiModel.
  return PagingData.insertSeparators(uiModelPagingData,
    (@Nullable UiModel before, @Nullable UiModel after) -> {
      if (before == null) {
        return new UiModel.SeparatorModel("HEADER");
      } else if (after == null) {
        return new UiModel.SeparatorModel("FOOTER");
      } else if (shouldSeparate(before, after)) {
        return new UiModel.SeparatorModel("BETWEEN ITEMS "
          + before.toString() + " AND " + after.toString());
      } else {
        // Return null to avoid adding a separator between two
        // items.
        return null;
      }
    });
});

// Map outer stream, so you can perform transformations on each
// paging generation.
Transformations.map(PagingLiveData.getLiveData(pager),
  pagingData -> {
    // First convert items in stream to UiModel.UserModel.
    PagingData<UiModel> uiModelPagingData = pagingData.map(
      UiModel.UserModel::new);

    // Insert UiModel.SeparatorModel, which produces PagingData of
    // generic type UiModel.
    return PagingData.insertSeparators(uiModelPagingData,
      (@Nullable UiModel before, @Nullable UiModel after) -> {
        if (before == null) {
          return new UiModel.SeparatorModel("HEADER");
        } else if (after == null) {
          return new UiModel.SeparatorModel("FOOTER");
        } else if (shouldSeparate(before, after)) {
          return new UiModel.SeparatorModel("BETWEEN ITEMS "
            + before.toString() + " AND " + after.toString());
        } else {
          // Return null to avoid adding a separator between two
          // items.
          return null;
        }
      });
  });

class UiModelAdapter :
  PagingDataAdapter<UiModel, RecyclerView.ViewHolder>(UiModelComparator) {

  override fun onCreateViewHolder(
    parent: ViewGroup,
    viewType: Int
  ) = when (viewType) {
    R.layout.item -> UserModelViewHolder(parent)
    else -> SeparatorModelViewHolder(parent)
  }

  override fun getItemViewType(position: Int) {
    // Use peek over getItem to avoid triggering page fetch / drops, since
    // recycling views is not indicative of the user's current scroll position.
    return when (peek(position)) {
      is UiModel.UserModel -> R.layout.item
      is UiModel.SeparatorModel -> R.layout.separator_item
      null -> throw IllegalStateException("Unknown view")
    }
  }

  override fun onBindViewHolder(
    holder: RecyclerView.ViewHolder,
    position: Int
  ) {
    val item = getItem(position)
    if (holder is UserModelViewHolder) {
      holder.bind(item as UserModel)
    } else if (holder is SeparatorModelViewHolder) {
      holder.bind(item as SeparatorModel)
    }
  }
}

object UiModelComparator : DiffUtil.ItemCallback<UiModel>() {
  override fun areItemsTheSame(
    oldItem: UiModel,
    newItem: UiModel
  ): Boolean {
    val isSameRepoItem = oldItem is UiModel.UserModel
      && newItem is UiModel.UserModel
      && oldItem.id == newItem.id

    val isSameSeparatorItem = oldItem is UiModel.SeparatorModel
      && newItem is UiModel.SeparatorModel
      && oldItem.description == newItem.description

    return isSameRepoItem || isSameSeparatorItem
  }

  override fun areContentsTheSame(
    oldItem: UiModel,
    newItem: UiModel
  ) = oldItem == newItem
}

class UiModelAdapter extends PagingDataAdapter<UiModel, RecyclerView.ViewHolder> {
  UiModelAdapter() {
    super(new UiModelComparator(), Dispatchers.getMain(),
      Dispatchers.getDefault());
  }

  @NonNull
  @Override
  public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent,
    int viewType) {
    if (viewType == R.layout.item) {
      return new UserModelViewHolder(parent);
    } else {
      return new SeparatorModelViewHolder(parent);
    }
  }

  @Override
  public int getItemViewType(int position) {
    // Use peek over getItem to avoid triggering page fetch / drops, since
    // recycling views is not indicative of the user's current scroll position.
    UiModel item = peek(position);
    if (item instanceof UiModel.UserModel) {
      return R.layout.item;
    } else if (item instanceof UiModel.SeparatorModel) {
      return R.layout.separator_item;
    } else {
      throw new IllegalStateException("Unknown view");
    }
  }

  @Override
  public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder,
    int position) {
    if (holder instanceOf UserModelViewHolder) {
      UserModel userModel = (UserModel) getItem(position);
      ((UserModelViewHolder) holder).bind(userModel);
    } else {
      SeparatorModel separatorModel = (SeparatorModel) getItem(position);
      ((SeparatorModelViewHolder) holder).bind(separatorModel);
    }
  }
}

class UiModelComparator extends DiffUtil.ItemCallback<UiModel> {
  @Override
  public boolean areItemsTheSame(@NonNull UiModel oldItem,
    @NonNull UiModel newItem) {
    boolean isSameRepoItem = oldItem instanceof UserModel
      && newItem instanceof UserModel
      && ((UserModel) oldItem).getId().equals(((UserModel) newItem).getId());

    boolean isSameSeparatorItem = oldItem instanceof SeparatorModel
      && newItem instanceof SeparatorModel
      && ((SeparatorModel) oldItem).getDescription().equals(
      ((SeparatorModel) newItem).getDescription());

    return isSameRepoItem || isSameSeparatorItem;
  }

  @Override
  public boolean areContentsTheSame(@NonNull UiModel oldItem,
    @NonNull UiModel newItem) {
    return oldItem.equals(newItem);
  }
}

class UiModelAdapter extends PagingDataAdapter<UiModel, RecyclerView.ViewHolder> {
  UiModelAdapter() {
    super(new UiModelComparator(), Dispatchers.getMain(),
      Dispatchers.getDefault());
  }

  @NonNull
  @Override
  public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent,
    int viewType) {
    if (viewType == R.layout.item) {
      return new UserModelViewHolder(parent);
    } else {
      return new SeparatorModelViewHolder(parent);
    }
  }

  @Override
  public int getItemViewType(int position) {
    // Use peek over getItem to avoid triggering page fetch / drops, since
    // recycling views is not indicative of the user's current scroll position.
    UiModel item = peek(position);
    if (item instanceof UiModel.UserModel) {
      return R.layout.item;
    } else if (item instanceof UiModel.SeparatorModel) {
      return R.layout.separator_item;
    } else {
      throw new IllegalStateException("Unknown view");
    }
  }

  @Override
  public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder,
    int position) {
    if (holder instanceOf UserModelViewHolder) {
      UserModel userModel = (UserModel) getItem(position);
      ((UserModelViewHolder) holder).bind(userModel);
    } else {
      SeparatorModel separatorModel = (SeparatorModel) getItem(position);
      ((SeparatorModelViewHolder) holder).bind(separatorModel);
    }
  }
}

class UiModelComparator extends DiffUtil.ItemCallback<UiModel> {
  @Override
  public boolean areItemsTheSame(@NonNull UiModel oldItem,
    @NonNull UiModel newItem) {
    boolean isSameRepoItem = oldItem instanceof UserModel
      && newItem instanceof UserModel
      && ((UserModel) oldItem).getId().equals(((UserModel) newItem).getId());

    boolean isSameSeparatorItem = oldItem instanceof SeparatorModel
      && newItem instanceof SeparatorModel
      && ((SeparatorModel) oldItem).getDescription().equals(
      ((SeparatorModel) newItem).getDescription());

    return isSameRepoItem || isSameSeparatorItem;
  }

  @Override
  public boolean areContentsTheSame(@NonNull UiModel oldItem,
    @NonNull UiModel newItem) {
    return oldItem.equals(newItem);
  }
}

pager.flow // Type is Flow<PagingData<User>>.
  .map { pagingData ->
    pagingData.filter { user -> !user.hiddenFromUi }
      .map { user -> UiModel.UserModel(user) }
  }
  .cachedIn(viewModelScope)

// CoroutineScope helper provided by the lifecycle-viewmodel-ktx artifact.
CoroutineScope viewModelScope = ViewModelKt.getViewModelScope(viewModel);
PagingRx.cachedIn(
  // Type is Flowable<PagingData<User>>.
  PagingRx.getFlowable(pager)
    .map(pagingData -> pagingData
      .filter(user -> !user.isHiddenFromUi())
      .map(UiModel.UserModel::new)),
  viewModelScope);
}

// CoroutineScope helper provided by the lifecycle-viewmodel-ktx artifact.
CoroutineScope viewModelScope = ViewModelKt.getViewModelScope(viewModel);
PagingLiveData.cachedIn(
  Transformations.map(
    // Type is LiveData<PagingData<User>>.
    PagingLiveData.getLiveData(pager),
    pagingData -> pagingData
      .filter(user -> !user.isHiddenFromUi())
      .map(UiModel.UserModel::new)),
  viewModelScope);