使用房间更新PagingLibrary中的列表项目(仅限网络)

Question

我正在使用Paging Library从网络加载数据ItemKeyedDataSource.在获取项目后,用户可以编辑它们,此更新在内存缓存中完成(不使用像Room这样的数据库).

现在因为它PagedList本身无法更新(这里讨论),我必须重新创建PagedList并传递给它PagedListAdapter.

更新本身没有问题,但在recyclerView使用new 更新后PagedList,列表会跳转到列表的开头,从而破坏前一个滚动位置.无论如何更新PagedList同时保持滚动位置(就像它如何与Room一起工作)？

DataSource以这种方式实现:

public class MentionKeyedDataSource extends ItemKeyedDataSource<Long, Mention> {

    private Repository repository;
    ...
    private List<Mention> cachedItems;

    public MentionKeyedDataSource(Repository repository, ..., List<Mention> cachedItems){
        super();

        this.repository = repository;
        this.teamId = teamId;
        this.inboxId = inboxId;
        this.filter = filter;
        this.cachedItems = new ArrayList<>(cachedItems);
    }

    @Override
    public void loadInitial(@NonNull LoadInitialParams<Long> params, final @NonNull ItemKeyedDataSource.LoadInitialCallback<Mention> callback) {
        Observable.just(cachedItems)
                .filter(() -> return cachedItems != null && !cachedItems.isEmpty())
                .switchIfEmpty(repository.getItems(..., params.requestedLoadSize).map(...))
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(response -> callback.onResult(response.data.list));
    }

    @Override
    public void loadAfter(@NonNull LoadParams<Long> params, final @NonNull ItemKeyedDataSource.LoadCallback<Mention> callback) {
        repository.getOlderItems(..., params.key, params.requestedLoadSize)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(response -> callback.onResult(response.data.list));
    }

    @Override
    public void loadBefore(@NonNull LoadParams<Long> params, final @NonNull ItemKeyedDataSource.LoadCallback<Mention> callback) {
        repository.getNewerItems(..., params.key, params.requestedLoadSize)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(response -> callback.onResult(response.data.list));
    }

    @NonNull
    @Override
    public Long getKey(@NonNull Mention item) {
        return item.id;
    }
}

该PagedList创建这样的:

PagedList.Config config = new PagedList.Config.Builder()
        .setPageSize(PAGE_SIZE)
        .setInitialLoadSizeHint(preFetchedItems != null && !preFetchedItems.isEmpty()
                ? preFetchedItems.size()
                : PAGE_SIZE * 2
        ).build();

pagedMentionsList = new PagedList.Builder<>(new MentionKeyedDataSource(mRepository, team.id, inbox.id, mCurrentFilter, preFetchedItems)
        , config)
        .setFetchExecutor(ApplicationThreadPool.getBackgroundThreadExecutor())
        .setNotifyExecutor(ApplicationThreadPool.getUIThreadExecutor())
        .build();

该PagedListAdapter创建这样的:

public class ItemAdapter extends PagedListAdapter<Item, ItemAdapter.ItemHolder> { //Adapter from google guide, Nothing special here.. }

mAdapter = new ItemAdapter(new DiffUtil.ItemCallback<Mention>() {
            @Override
            public boolean areItemsTheSame(Item oldItem, Item newItem) {
                return oldItem.id == newItem.id;
            }

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

,并像这样更新:

mAdapter.submitList(pagedList);

PS:如果有更好的方法来更新列表项而不使用Room请分享.

Answer 1

您所需要做的就是DataSource每次更新数据时使当前无效。

我会做什么：

• 将网络逻辑从新类移至MentionKeyedDataSource新类，PagedList.BoundaryCallback在构建PagedList.

• 将所有数据移动到DataProvider保存所有下载数据并引用 的某个位置DataSource。每次更新数据时都会使DataProvider当前无效DataSource

也许是这样的事情

    val dataProvider = PagedDataProvider()
    val dataSourceFactory = InMemoryDataSourceFactory(dataProvider = dataProvider)

在哪里

class PagedDataProvider : DataProvider<Int, DataRow> {

    private val dataCache = mutableMapOf<Int, List<DataRow>>()
    override val sourceLiveData = MutableLiveData<DataSource<Int, DataRow>>()

    //implement data add/remove/update here
    //and after each modification call
    //sourceLiveData.value?.invalidate()
}

和

class InMemoryDataSourceFactory<Key, Value>(
    private val dataProvider: DataProvider<Key, Value>
) : DataSource.Factory<Key, Value>() {

    override fun create(): DataSource<Key, Value> {
        val source = InMemoryDataSource(dataProvider = dataProvider)
        dataProvider.sourceLiveData.postValue(source)
        return source
    }
}

Room这种方法与每次更新表行时当前的行都DataSource无效并创建新的数据源非常相似DataSourceFactory。