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我正在构建一个应用程序，它使用 ArticleBoundaryCallback 来启动对 API 的调用，并将响应存储在 Room 中。我还在使用 LiveData 收听该表，并在 PagedListAdapter 中显示项目。

问题是每次在 Room 的（Article）表中插入新数据时，整个列表都会刷新。

此外，在配置更改时，似乎再次获取了整个数据（ViewModel 不保留它，RecyclerView 被重新创建）。

在每次插入时，RecyclerView 都会跳转（如果插入了新数据，则跳转几行，或者如果它用旧数据替换新数据，则在开头）。

整个代码在这个GitHub repo中。

我的课程是：

文章：

@Entity(tableName = "article",
    indices={@Index(value="id")})public class Article {
@PrimaryKey(autoGenerate = false)
@SerializedName("_id")
@Expose
@NonNull
private String id;
@SerializedName("web_url")
@Expose
private String webUrl;
@SerializedName("snippet")
@Expose
private String snippet;
@SerializedName("print_page")
@Expose
private String printPage;
@SerializedName("source")
@Expose
private String source;
@SerializedName("multimedia")
@Expose
@Ignore
private List<Multimedium> multimedia = null;

文章 DAO：

@Dao
public interface ArticleDao {

@Insert(onConflict = OnConflictStrategy.REPLACE)
long insert(Article article);

@Insert(onConflict = OnConflictStrategy.REPLACE)
void update(Article... repos);

@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertArticles(List<Article> articles);


@Delete
void delete(Article... articles);

@Query("DELETE FROM article")
void deleteAll();

@Query("SELECT * FROM article")
List<Article> getArticles();

@Query("SELECT * FROM article")
DataSource.Factory<Integer, Article> getAllArticles();}

LocalCache（从 Room 存储/检索）

public class LocalCache {
private static final String TAG = LocalCache.class.getSimpleName();
private ArticleDao articleDao;
private Executor ioExecutor;

public LocalCache(AppDatabase appDatabase, Executor ioExecutor) {
    this.articleDao = appDatabase.getArticleDao();
    this.ioExecutor = ioExecutor;
}

public void insertAllArticles(List<Article> articleArrayList){
    ioExecutor.execute(new Runnable() {
        @Override
        public void run() {
            Log.d(TAG, "inserting " + articleArrayList.size() + " repos");
            articleDao.insertArticles(articleArrayList);
        }
    });
}

public void otherFunction(ArrayList<Article> articleArrayList){
    // TODO
}

public DataSource.Factory<Integer, Article> getAllArticles() {
    return articleDao.getAllArticles();
}

应用程序库

public class AppRepository {

private static final String TAG = AppRepository.class.getSimpleName();
private static final int DATABASE_PAGE_SIZE = 20;
private Service service;
private LocalCache localCache;
private LiveData<PagedList<Article>> mPagedListLiveData;

public AppRepository(Service service, LocalCache localCache) {
    this.service = service;
    this.localCache = localCache;
}

/**
 * Search - match the query.
 */
public ApiSearchResultObject search(String q){
    Log.d(TAG, "New query: " + q);

    // Get data source factory from the local cache
    DataSource.Factory dataSourceFactory = localCache.getAllArticles();

    // every new query creates a new BoundaryCallback
    // The BoundaryCallback will observe when the user reaches to the edges of
    // the list and update the database with extra data
    ArticleBoundaryCallback boundaryCallback = new ArticleBoundaryCallback(q, service, localCache);

    // Get the paged list
    LiveData data = new LivePagedListBuilder(dataSourceFactory, DATABASE_PAGE_SIZE)
            .setBoundaryCallback(boundaryCallback)
            .build();

    mPagedListLiveData = data;

    ApiSearchResultObject apiSearchResultObject = new ApiSearchResultObject();
    apiSearchResultObject.setArticles(data);

    return apiSearchResultObject;
}

public DataSource.Factory getAllArticles() {
    return localCache.getAllArticles();
}

public void insertAllArticles(ArrayList<Article> articleList) {
    localCache.insertAllArticles(articleList);
}
}

视图模型

public class DBArticleListViewModel extends ViewModel {

private AppRepository repository;

// init a mutable live data to listen for queries
private MutableLiveData<String> queryLiveData = new MutableLiveData();

// make the search after each new search item is posted with (searchRepo) using "map"
private LiveData<ApiSearchResultObject> repositoryResult =  Transformations.map(queryLiveData, queryString -> {
    return repository.search(queryString);
});

// constructor, init repo
public DBArticleListViewModel(@NonNull AppRepository repository) {
    this.repository = repository;
}

// get my Articles!!
public LiveData<PagedList<Article>> articlesLiveData = Transformations.switchMap(repositoryResult, object ->
        object.getArticles());

// get teh Network errors!
public LiveData<String> errorsLiveData = Transformations.switchMap(repositoryResult, object ->
        object.getNetworkErrors());


// Search REPO
public final void searchRepo(@NonNull String queryString) {
    this.queryLiveData.postValue(queryString);
}

// LAST Query string used
public final String lastQueryValue() {
    return (String)this.queryLiveData.getValue();
}

活动 - 从 VM 观察

 DummyPagedListAdapter articleListAdapter = new DummyPagedListAdapter(this);

    localDBViewModel = ViewModelProviders.of(this, Injection.provideViewModelFactory(this)).get(DBArticleListViewModel.class);

    localDBViewModel.articlesLiveData.observe(this, pagedListLiveData ->{
        Log.d(TAG, "articlesLiveData.observe size: " + pagedListLiveData.size());
        if(pagedListLiveData != null)
            articleListAdapter.submitList(pagedListLiveData);
    });

    recyclerView.setAdapter(articleListAdapter);

适配器

public class DummyPagedListAdapter extends PagedListAdapter<Article, ArticleViewHolder> {

private final ArticleListActivity mParentActivity;

public DummyPagedListAdapter(ArticleListActivity parentActivity) {
    super(Article.DIFF_CALLBACK);
    mParentActivity = parentActivity;
}

@NonNull
@Override
public ArticleViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(mParentActivity).inflate(R.layout.article_list_content, parent, false);
    return new ArticleViewHolder(itemView);
}

@Override
public void onBindViewHolder(@NonNull ArticleViewHolder holder, int position) {
    Article article = getItem(position);

    if (article != null) {
        holder.bindTo(article);
    } else {
        holder.clear();
    }
}
}

差异

   public static DiffUtil.ItemCallback<Article> DIFF_CALLBACK = new 
DiffUtil.ItemCallback<Article>() {
    @Override
    public boolean areItemsTheSame(@NonNull Article oldItem, @NonNull 
Article newItem) {
        return oldItem.getId() == newItem.getId();
    }

    @Override
    public boolean areContentsTheSame(@NonNull Article oldItem, @NonNull 
Article newItem) {
        return oldItem.getWebUrl() == newItem.getWebUrl();
    }
};

我真的需要解决这个问题。谢谢！

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1 回答 1

6

是的..我花了一段时间，但我解决了。正如我所想的，愚蠢的问题：在适配器用来决定从观察到的数据集中添加什么和忽略什么的 DIFF_CALLBACK 中，我使用比较器 oldItem.getId() == newItem.getId() 这是字符串！ ！！当然，适配器总是得到“新值”并添加它们..

更正了 DiffUtil.ItemCallback

 public static DiffUtil.ItemCallback<Article> DIFF_CALLBACK = new DiffUtil.ItemCallback<Article>() {
    @Override
    public boolean areItemsTheSame(@NonNull Article oldItem, @NonNull Article newItem) {
        return oldItem.getStoreOrder() == newItem.getStoreOrder();
    }

    @Override
    public boolean areContentsTheSame(@NonNull Article oldItem, @NonNull Article newItem) {
        return oldItem.getId().equals(newItem.getId()) && oldItem.getWebUrl().equals(newItem.getWebUrl());
    }
};

我希望这将提醒我们始终关注最基本的事情。我为此浪费了很多时间。希望你不会:)

于 2018-07-23T10:28:46.850 回答