线程——如何提高App的性能

Question

我正在制作一个应用程序，它可以扫描 phone 存储中的歌曲列表并将它们存储在 ListView 中。所以，我创建了 class SongsManager 扫描 SD 卡中的歌曲并将它们存储在 Array 中。代码如下。

public class SongsManager {
final String MEDIA_PATH = Environment.getExternalStorageDirectory() .getPath() + "/";
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
private String mp3Pattern = ".mp3";
private File directory;

// Constructor
 public SongsManager() {
 }

/** * Function to read all mp3 files and store the details in * ArrayList * */

public ArrayList<HashMap<String, String>> getPlayList() {
            System.out.println(MEDIA_PATH);
            if (MEDIA_PATH != null) {
                File home = new File(MEDIA_PATH);
                File[] listFiles = home.listFiles();
                if (listFiles != null && listFiles.length > 0) {
                    for (File file : listFiles) {
                        System.out.println(file.getAbsolutePath());
                        if (file.isDirectory()) {
                            scanDirectory(file);
                        } else {
                            addSongToList(file);
                        }
                    }
                }
            }
    return songsList;
}


private void scanDirectory(final File directory) {
            if (directory != null) {
                File[] listFiles = directory.listFiles();
                if (listFiles != null && listFiles.length > 0) {
                    for (File file : listFiles) {
                        if (file.isDirectory()) {
                            scanDirectory(file);
                        } else {
                            addSongToList(file);
                        }
                    }
                }
            }
    }


private void addSongToList(File song) {
    if (song.getName().endsWith(mp3Pattern)) {
        HashMap<String, String> songMap = new HashMap<String, String>();
        songMap.put("songTitle", song.getName().substring(0, (song.getName().length() - 4)));
        songMap.put("songPath", song.getPath());

        // Adding each song to SongList
        songsList.add(songMap);
    }
}
 }

当我运行应用程序时，由于从 SD 卡获取歌曲，应用程序会冻结 2 或 3 秒。当我打开 logcat 时，它显示错误 The application may be doing too much work on its main thread。所以，我决定提高应用程序的性能。我修改了 class 如下

 public class SongsManager {

final String MEDIA_PATH = Environment.getExternalStorageDirectory() .getPath() + "/";
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
private String mp3Pattern = ".mp3";
private File directory;

// Constructor
 public SongsManager() {
 }

/** * Function to read all mp3 files and store the details in * ArrayList * */

public ArrayList<HashMap<String, String>> getPlayList() {
            System.out.println(MEDIA_PATH);
            if (MEDIA_PATH != null) {
                File home = new File(MEDIA_PATH);
                File[] listFiles = home.listFiles();
                if (listFiles != null && listFiles.length > 0) {
                    for (File file : listFiles) {
                        System.out.println(file.getAbsolutePath());
                        if (file.isDirectory()) {
                            scanDirectory(file);
                        } else {
                            addSongToList(file);
                        }
                    }
                }
            }
    return songsList;
}


private void scanDirectory(final File directory) {
    Runnable r = new Runnable() {
        @Override
        public void run() {
            if (directory != null) {
                File[] listFiles = directory.listFiles();
                if (listFiles != null && listFiles.length > 0) {
                    for (File file : listFiles) {
                        if (file.isDirectory()) {
                            scanDirectory(file);
                        } else {
                            addSongToList(file);
                        }
                    }
                }
            }
        }
    };
    Thread thread = new Thread(r);
    thread.start();
}


private void addSongToList(File song) {
    if (song.getName().endsWith(mp3Pattern)) {
        HashMap<String, String> songMap = new HashMap<String, String>();
        songMap.put("songTitle", song.getName().substring(0, (song.getName().length() - 4)));
        songMap.put("songPath", song.getPath());

        // Adding each song to SongList
        songsList.add(songMap);
    }
}
}

修改代码后，冻结问题解决，但无法正常获取歌曲。当我打开应用程序时，有些歌曲已加载，有些则没有。当我重新打开应用程序时，会加载更多歌曲。出现此问题。这是我的 Tab1 Class 代码

public class Tab1 extends ListFragment {

private ListView lv;
// Songs list
public ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();


public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View V = inflater.inflate(R.layout.tab1, container, false);

    ArrayList<HashMap<String, String>> songsListData = new ArrayList<HashMap<String, String>>();
    SongsManager plm = new SongsManager();
    // get all songs from sdcard
    this.songsList = plm.getPlayList();

    // looping through playlist
    for (int i = 0; i < songsList.size(); i++) {
        // creating new HashMap
        HashMap<String, String> song = songsList.get(i);
        // adding HashList to ArrayList
        songsListData.add(song);
    }

    // Adding menuItems to ListView
    ListAdapter adapter = new SimpleAdapter(getContext(), songsListData,
            R.layout.playlist_item, new String[]{"songTitle"}, new int[]{
            R.id.songTitle});
    setListAdapter(adapter);
    return V;
}

}

Answer 1

考虑使用 AsyncTask 而不是上述实现。在您的实现中，无法保证在您的 plm.getPlaylist() 完成后扫描所有歌曲，因为它是在多个不同的平台上完成的线程。这就是为什么您没有看到所有歌曲的原因。

public class GetSongsAsyncTask extends AsyncTask<Void, Void, List<Hashmap<String, String>>> {
private final SongsManager mSongsManager;

public interface SongsReceivedListener {
    void onSongsReceived(List<HashMap<String, String>> songs);
}

private SongsReceivedListener mSongsReceivedListener;

public GetSongsAsyncTask(SongsReceivedListener mSongsReceivedListener) {
    this.mSongsReceivedListener = mSongsReceivedListener;
    mSongsManager = new SongsManager();
}

@Override
protected List<HashMap<String, String>> doInBackground(Void.. voids) {
    return mSongsManager.getPLayList();
}

@Override
protected void onPostExecute(List<HashMap<String, String>> v) {
    if(mSongsReceivedListener != null) {
        mSongsReceivedListener.onSongsReceived(v);
    }
}
}

您的列表片段将在其中实现 SongsReceivedListener 并像这样调用此 AsyncTask

new GetSongsAsyncTask(this).execute();

你的 ListFragment 看起来像这样

public class Tab1 扩展 ListFragment 实现 GetSongsAsyncTask.SongsReceivedListener{

私有ListView lv； // 歌曲列表 public ArrayList> songsList = new ArrayList>(); public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); }

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View V = inflater.inflate(R.layout.tab1, container, false);
    new GetSongsAsyncTask(this).execute(); 
    return V;
}

@Override
void onSongsReceived(List<Hashmap<String, String>> songs) {
  if(getContext() == null)
   return;
  // looping through playlist
  for (int i = 0; i < songsList.size(); i++) {
      // creating new HashMap
      HashMap<String, String> song = songs.get(i);
      // adding HashList to ArrayList
      songsListData.add(song);
  }

  // Adding menuItems to ListView
  ListAdapter adapter = new SimpleAdapter(getContext(), songsListData,
          R.layout.playlist_item, new String[]{"songTitle"}, new int[]{
          R.id.songTitle});
  setListAdapter(adapter);
}

}

线程——如何提高App的性能

Threading - how to improve the performance of App

multithreading

android

runnable