在回收者视图中加载大量项目

Question

我在片段中有一个回收站视图，基本上我试图在回收站视图中加载歌曲列表。回收站视图的每一行都包含一个 imageview（用于专辑封面）和 textview（歌曲名称）。当数据集的大小很大时，我遇到了麻烦，即当歌曲太多时，回收器视图滞后，应用程序最终给出 ANR.I 我正在使用 Glide 在每一行的图像视图中加载专辑封面。 google 音乐播放器如何能够毫无延迟地播放如此多的歌曲？

编辑： 这是我的 SongsFragment

public class SongsFragment extends Fragment {
static {
    AppCompatDelegate.setCompatVectorFromResourcesEnabled(true);
}
ProgressBar progressBar;    // progress bar to show after every 30 items
NestedScrollView nestedScrollView;  //for smooth scrolling of recyclerview as well as to detect the end of recyclerview
RecyclerView recyclerView;
ArrayList<Song> songMainList = new ArrayList<>();  //partial list in which items are added
ArrayList<Song> songAllList = new ArrayList<>(); //Complete List of songs
SongAdapter songsAdapter;
private LinearLayoutManager layoutManager;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_songs, container, false);

    nestedScrollView = (NestedScrollView) rootView.findViewById(R.id.nestedScrollView);
    progressBar = (ProgressBar) rootView.findViewById(R.id.progressBar);

    String songJson = getActivity().getIntent().getStringExtra("songList");
    songAllList = new Gson().fromJson(songJson, new TypeToken<ArrayList<Song>>() {
    }.getType());
            //Getting list of all songs in songAllList

    if (songAllList.size() > 30) {  
        songMainList = new ArrayList<>(songAllList.subList(0,30));
    } else {
        songMainList = songAllList;
    }

    //if size of fetched songAllList>30 then add only 30 rows to songMainList

    recyclerView = (RecyclerView) rootView.findViewById(R.id.songs);
    int spanCount = 1; // 2 columns
    int spacing = 4; // 50px
    recyclerView.addItemDecoration(new GridItemDecoration(spanCount, spacing, true));
    recyclerView.setHasFixedSize(true);
    recyclerView.setNestedScrollingEnabled(false);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    songsAdapter = new SongAdapter(getActivity(), songMainList, recyclerView);

    nestedScrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
        @Override
        public void onScrollChanged() {
            View view = (View) nestedScrollView.getChildAt(nestedScrollView.getChildCount() - 1);
            int diff = (view.getBottom() - (nestedScrollView.getHeight() + nestedScrollView
                    .getScrollY()));

            if (diff == 0) {    //NestedScrollView scrolled to bottom
                progressBar.setVisibility(View.VISIBLE);    //show progressbar
                new Handler().postDelayed(new Runnable() { 
                    @Override
                    public void run() {
                        if (songMainList.size() < songAllList.size()) {
                            int x = 0, y = 0;
                            if ((songAllList.size() - songMainList.size()) >= 30) {
                                x = songMainList.size();
                                y = x + 30;
                            } else {
                                x = songMainList.size();
                                y = x + songAllList.size() - songMainList.size();
                            }
                            for (int i = x; i < y; i++) {
                                songMainList.add(songAllList.get(i));   //Adding new items from songAllList to songMainList one by one
                                songsAdapter.notifyDataSetChanged();
                            }
                        }
                        progressBar.setVisibility(View.GONE);
                    }
                }, 1500);


            }
        }
    });
    recyclerView.setAdapter(songsAdapter);


    return rootView;
    }
}

这是我的 RecyclerViewAdapter 和 viewholder

public class SongAdapter extends RecyclerView.Adapter {

private List<Song> songsList;
private Context c;

private RecyclerView.ViewHolder holder;

public SongAdapter(Context context) {
    mainActivityContext = context;
}

public SongAdapter(Context context, List<Song> songs, RecyclerView recyclerView) {
    songsList = songs;
    LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
    c = context;
}

public SongAdapter getInstance() {
    return SongAdapter.this;
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.song_list_row, parent, false);
    return new SongViewHolder(view,c);
}

@Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {

    if (holder instanceof SongViewHolder) {
        Song song = songsList.get(position);
        this.holder = holder;

        String name = song.getName();
        String artist = song.getArtist();
        String imagepath = song.getImagepath();

        ((SongViewHolder) holder).name.setText(name);

        ((SongViewHolder) holder).artist.setText(artist);

        if (!imagepath.equalsIgnoreCase("no_image")) //if the album art has valid  imagepath for this song

            Glide.with(c).load(imagepath)
                    .centerCrop()
                    .into(((SongViewHolder) holder).iv);
        else
            ((SongViewHolder) holder).iv.setImageResource(R.drawable.empty);

        ((SongViewHolder) holder).song = song;
    }
}

@Override
public int getItemCount() {
    return songsList.size();
}

static class SongViewHolder extends RecyclerView.ViewHolder{

    ImageView iv;
    TextView name, artist;
    CardView songListCard;
    private Context ctx;

    private OnLongPressListener mListener;

    SongViewHolder(View v, Context context) {
        super(v);
        this.ctx = context;
        iv= (ImageView) v.findViewById(R.id.album_art);
        name= (TextView) v.findViewById(R.id.name);
        artist= (TextView) v.findViewById(R.id.artist_mini);
        songListCard = (CardView) v.findViewById(R.id.song_list_card);
    }
}

当只有 150-200 个项目时，recyclerview 工作正常，但当达到 600-700 个项目时，整个应用程序变慢。这可能是因为我在 onBindViewHolder?

中使用 glide 的方式

Answer 1

你们是一次性加载所有数据吗？ RecycleView 应该没有问题，我认为如果你有太多数据，处理本身会花费太多时间。您应该分块加载数据并检查用户的滚动状态并加载下一批等。有点像 Instagram 或 Facebook 的做法。

Answer 2

通过删除 recyclerview 上的 NestedScrollView 解决了问题。 nestedscrollview 不允许调用 recyclerview.addOnScrollListener() ，因此我在加载更多项目时出现滞后。这是我如何为 RecyclerView 实现 loadOnScroll-

 recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            if (!recyclerView.canScrollVertically(1))
                onScrolledToBottom();
        }
    });

private void onScrolledToBottom() {
    if (songMainList.size() < songAllList.size()) {
        int x, y;
        if ((songAllList.size() - songMainList.size()) >= 50) {
            x = songMainList.size();
            y = x + 50;
        } else {
            x = songMainList.size();
            y = x + songAllList.size() - songMainList.size();
        }
        for (int i = x; i < y; i++) {
            songMainList.add(songAllList.get(i));
        }
        songsAdapter.notifyDataSetChanged();
    }

}

Answer 3

排序答案：

LinearLayoutManager(context).apply { isAutoMeasureEnabled = false }
// or in Java
layoutManager.setAutoMeasureEnabled(false)

更新 2020.08.14

已弃用 RecyclerView.LayoutManager#setAutoMeasureEnabled

此方法已在 API 级别 27.1.0 中弃用。 LayoutManager 的实现者应该通过覆盖 isAutoMeasureEnabled()

来定义它是否使用 AutoMeasure

从 RecyclerView.LayoutManager#setAutoMeasureEnabled() 的文档我们知道：

This method is usually called by the LayoutManager with value {@code true} if it wants to support WRAP_CONTENT

It works by calling {@link LayoutManager#onLayoutChildren(Recycler, State)} during an {@link RecyclerView#onMeasure(int, int)} call, then calculating desired dimensions based on children's positions.

如果我们设置 mAutoMeasure = true，它将在 RecyclerView#onMeasure(int, int) 调用期间调用 LayoutManager#onLayoutChildren(Recycler, State)。每个子视图的onMeasure()方法都会被调用，这太费时间了。

我们来看LinearLayoutManager的构造函数

public LinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
    setOrientation(orientation);
    setReverseLayout(reverseLayout);
    setAutoMeasureEnabled(true);
}

所以，我们设置mAutoMeasure = false后，一切就OK了

Answer 4

您可以使用 AndroidX Room & Paging 实现此目的

将您的数据从网络缓存到本地房间数据库
使用 Paging 从房间数据库加载数据

在回收者视图中加载大量项目

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