OutOfMemoryError 使用 FirebaseRecyclerViewAdapter

Question

我正在构建一个 android 应用程序来播放有声读物。有声读物元数据（标题、作者等）使用以下结构存储在 Firebase 数据库中：

root
  --- audioBooks
    --- <individual hash for each book>
      --- author: "Ray Bradbury"
      --- title: "Fahrenheit 451"
      --- finished: false
      --- key: <individual hash for each book>
      --- cover
        --- b64Cover: <b64-encoded image>
        --- backgroundColor: -14473711
        --- ...
      --- tracks
        --- 0
          --- title: "Track 1"
          --- duration: 361273
          --- finished: false
          --- currentPosition: 12345
          --- ...
        --- 1
          --- ...
      --- currentTrack
        --- title: "Track 1"
        --- duration: 361273
        --- finished: false
        --- currentPosition: 12345
        --- ...

我有三个模型类用于 AudioBook、AudioBookTrack 和 AudioBookCover（删除了 setter 和 getter 以获得更好的概览）。

public class AudioBook {
    private String title;
    private String author;
    private int duration;
    private boolean finished;
    private String key;
    private AudioBookCover cover;
    private ArrayList<AudioBookTrack> tracks;
    private AudioBookTrack currentTrack;

    public AudioBook() {
    }

    public AudioBook(String title, String author, boolean finished, String key, AudioBookCover cover, ArrayList<AudioBookTrack> tracks, AudioBookTrack currentTrack) {
        this.title = title;
        this.author = author;
        this.finished = finished;
        this.key = key;
        this.cover = cover;
        this.tracks = tracks;
        this.currentTrack = currentTrack;
    }
}

public class AudioBookTrack {
    private String title;
    private String album;
    private String author;
    private String filePath;
    private int duration;
    private int currentPosition;
    private int index;
    private boolean finished;
    private String key;

    public AudioBookTrack() {
    }

    public AudioBookTrack(String title, String album, String author, String filePath, int duration, int currentPosition, int index, boolean finished, String key) {
        this.title = title;
        this.album = album;
        this.author = author;
        this.filePath = filePath;
        this.duration = duration;
        this.currentPosition = currentPosition;
        this.index = index;
        this.finished = finished;
        this.key = key;
    }
}

public class AudioBookCover {
    private String b64Cover;
    private int backgroundColor;
    private int primaryColor;
    private int secondaryColor;
    private int detailColor;

    public AudioBookCover() {
    }

    public AudioBookCover(String b64Cover, int backgroundColor, int primaryColor, int secondaryColor, int detailColor) {
        this.b64Cover = b64Cover;
        this.backgroundColor = backgroundColor;
        this.primaryColor = primaryColor;
        this.secondaryColor = secondaryColor;
        this.detailColor = detailColor;
    }
}

使用 Firebase 数据库中的数据并将其转换为模型类没有问题。但是，我现在想使用 FirebaseRecyclerViewAdapter 列出 RecyclerView 中的所有有声读物。这是在片段的 onCreateView() 方法中执行的代码：

mAudioBooksList = (RecyclerView) view.findViewById(R.id.audiobooks_list);
mAudioBooksList.setHasFixedSize(true);

ref = new Firebase(Constants.FIREBASE_URL).child("audioBooks");

mAdapter = new FirebaseRecyclerViewAdapter<AudioBook, AudioBooksViewHolder>(AudioBook.class, R.layout.audiobook_grid_item, AudioBooksViewHolder.class, ref) {
    @Override
    public void populateViewHolder(AudioBooksViewHolder audioBooksViewHolder, AudioBook audioBook) {
        audioBooksViewHolder.author.setText(audioBook.getAuthor());
        audioBooksViewHolder.title.setText(audioBook.getTitle());
        try {
            byte[] byteArray = Base64.decode(audioBook.getCover().getB64Cover());
            Bitmap coverBitmap = BitmapFactory.decodeByteArray(byteArray, 0, byteArray.length);
            audioBooksViewHolder.cover.setImageBitmap(coverBitmap);
        }
        catch(IOException e) {
            Log.e(TAG, "Could not decode album cover: " + e.getMessage());
        }
    }
};
mAudioBooksList.setAdapter(mAdapter);

这是 ViewHolder：

private static class AudioBooksViewHolder extends RecyclerView.ViewHolder {
TextView author;
TextView title;
ImageView cover;

public AudioBooksViewHolder(View itemView) {
    super(itemView);
    author = (TextView)itemView.findViewById(R.id.audiobook_grid_author);
    title = (TextView)itemView.findViewById(R.id.audiobook_grid_title);
    cover = (ImageView) itemView.findViewById(R.id.audiobook_grid_cover);
}

现在这段代码通常可以工作（我可以看到屏幕上显示的值），但是在很短的时间之后，应用程序由于 out-of-memory 错误而崩溃：

Uncaught exception in Firebase runloop (2.4.0). Please report to support@firebase.com
    java.lang.OutOfMemoryError: Failed to allocate a 35116844 byte allocation with 16773184 free bytes and 32MB until OOM
        at java.lang.StringFactory.newStringFromChars(Native Method)
        at java.lang.AbstractStringBuilder.toString(AbstractStringBuilder.java:629)
        at java.lang.StringBuilder.toString(StringBuilder.java:663)
        ...

我在物理 Nexus 5（没有模拟器）上测试应用程序。我猜这是因为我的嵌套模型（AudioBooks 中的 AudioBookTracks）导致了数百个 Java objects。不幸的是我不知道如何克服这个问题。对于仅列出有声读物，我不需要它们相应的有声读物曲目，但是由于有声读物曲目是有声读物的 child 元素，因此它们也会转换为 Java objects . 另一方面，我还尝试使用 ref.limitToFirst(2) 来限制显示的有声读物的数量。然后应用程序仍然崩溃，但需要更多时间才能崩溃。

您是否发现我的代码存在任何可能导致该问题的问题？或者是否有可能只 select 我需要的来自 Firebase 数据库的值，跳过例如有声书曲目？

谢谢！

Answer 1

这个问题确实很可能是因为您加载了很多关于每本书的不必要数据。特别是在移动设备上，您应该只加载要向用户显示的数据。由于 Firebase 始终加载整个节点，因此您必须建模您的数据，以便您可以仅加载您需要的数据。

解决方法是将曲目与有声读物的其他信息分开。这称为 denormalizing the data，是 NoSQL 数据库中非常常见的操作。

非规范化的数据将存储为：

root
  --- audioBooks
    --- <individual hash for each book>
      --- author: "Ray Bradbury"
      --- title: "Fahrenheit 451"
      --- finished: false
      --- key: <individual hash for each book>
      --- cover
        --- b64Cover: <b64-encoded image>
        --- backgroundColor: -14473711
        --- ...
  --- audioBookTracks
    --- <individual hash for each book>
      --- 0
        --- title: "Track 1"
        --- duration: 361273
        --- finished: false
        --- currentPosition: 12345
        --- ...
        --- 1
        --- ...
    --- currentTrack
      --- title: "Track 1"
      --- duration: 361273
      --- finished: false
      --- currentPosition: 12345
      --- ...

关于一本书的信息以及曲目存储在相同的 id（你称之为 "individual hash for each book"）下，但在不同的 top-level 节点下。关于书籍本身的数据在 audioBooks 下，而曲目列表在 authBookTracks.

下

现在您可以单独加载一本书的信息或该书的曲目：

ref.child("audioBooks").child(bookId).addValueEventListener(...

或

ref.child("audioBookTracks").child(bookId).addChildEventListener(...

您可以对 AudioBook Java class 建模以保留其 tracks 成员而不对其进行序列化（使用 Jackson 注释）。但您也可以将一本书及其曲目列表视为单独的 top-level 实体，它们恰好具有相同的 ID（这就是它在数据库中的建模方式）。

OutOfMemoryError 使用 FirebaseRecyclerViewAdapter

OutOfMemoryError using FirebaseRecyclerViewAdapter

java

android

out-of-memory

nosql

firebase