我正在构建一个用于播放有声读物的Android应用程序。有声书籍元数据（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AudioBook，AudioBookTrack和AudioBookCover的模型类（删除了setter和getter以获得更好的概述）。
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;
}
}
在Firebase数据库中使用数据并将其投射到模型类可以正常工作。但是我现在想要使用FirebaseRecyclerViewAdapter列出RecyclerView中的所有有声书。这是代码，在片段的onCreateView（）方法中执行：
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);
}
现在这段代码通常有效（我可以看到屏幕上显示的值），但是很短的时间后，应用程序因内存不足错误而崩溃：
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（无模拟器）上测试应用程序。 我想这是因为我的嵌套模型（AudioBooks中的AudioBookTracks）导致数百个Java对象。不幸的是我不知道如何克服这个问题。对于仅列出音频书籍，我不需要其相应的音频书籍轨道，但是音频书籍轨道是音频书籍的子元素，它们也被转换为Java对象。 另一方面，我也尝试使用ref.limitToFirst（2）来限制显示的有声书的数量。该应用程序仍然崩溃，但它需要更多的时间，直到它。
您是否发现我的代码存在任何可能导致问题的问题？或者是否有可能只从Firebase数据库中选择我需要的值，跳过例如有声读物跟踪？
谢谢！
答案 0 :(得分：1)
问题确实可能是因为您正在加载大量关于每本书的不必要数据。特别是在移动设备上，您应该只加载要显示给用户的数据。由于Firebase始终加载整个节点，因此您必须建模数据，以便只加载所需的数据。
解决方案是将音轨与有声书的其他信息分开。这称为denormalizing the data，是NoSQL数据库中非常常见的操作。
非规范化您将数据存储为：
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
--- ...
关于书籍和曲目的信息存储在相同的id（你称之为“每本书的单独哈希”）下，但是在不同的顶级节点下。有关图书本身的数据位于audioBooks下，而曲目列表位于authBookTracks下。
现在，您可以单独加载图书的信息或该图书的曲目：
ref.child("audioBooks").child(bookId).addValueEventListener(...
或
ref.child("audioBookTracks").child(bookId).addChildEventListener(...
您可以对AudioBook Java类进行建模以保留其tracks成员，而不是将其序列化（使用Jackson注释）。但是您也可以将一本书及其轨道列表视为具有相同ID的单独顶级实体（这是在数据库中建模的方式）。