我正在制作一个音乐播放器而且我想使用AsynTask。我的镜头就是它，但它似乎没有正常工作。 （致命异常AsyncTask＃1 也执行doInBackground时发生错误（））。到目前为止我得到了什么：
public class LoadingScreenActivity extends Activity {
private SharedPreferences sharedPrefs;
private String oldsongsListJson;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
sharedPrefs = PreferenceManager.getDefaultSharedPreferences(this);
CurrentData init = new CurrentData(); // Used to initialize static fields in CurrentData
// Load old songsList
oldsongsListJson = sharedPrefs.getString("songsList", "null");
if (!oldsongsListJson.equals("null")){
loadOldSettings();
}
else{
setContentView(R.layout.loading_screen);
new LoadLibrary().execute();
}
}
private void loadOldSettings(){
// Parse oldsongsListJson and do all of the library setup.
Gson gson = new Gson();
Type listType = new TypeToken<ArrayList<Song>>() {}.getType();
LibraryFiller libFill = new LibraryFiller(getApplicationContext());
LibraryInfo initializer = new LibraryInfo();
LibraryInfo.songsList = gson.fromJson(oldsongsListJson, listType);
libFill.buildLibraryFromSongsList();
Log.d("Library", "Old library Loaded");
// Check if there is a stored current song; if so, load it.
String oldSongJson = sharedPrefs.getString("currentSong", "null");
if(!oldSongJson.equals("null")){
CurrentData.currentSong = gson.fromJson(oldSongJson, Song.class);
}
else{
CurrentData.currentSong = null;
}
// Load old song index
CurrentData.currentSongIndex = sharedPrefs.getInt("currentSongIndex", 0);
// Load old playlist position
CurrentData.currentPlaylistPosition = sharedPrefs.getInt("currentPlaylistPosition", 0);
// Check if there is a stored playlist; if so, load it, else initialize a new one.
String oldPlaylistJson = sharedPrefs.getString("currentPlaylist", "null");
if (!oldPlaylistJson.equals("null")){
CurrentData.currentPlaylist = gson.fromJson(oldPlaylistJson, Playlist.class);
Log.d("Library", "Old playlist Loaded:" + oldPlaylistJson);
}
else{
CurrentData.currentPlaylist = new Playlist();
}
// Load the list of stored playlists
String oldPlaylistsJson = sharedPrefs.getString("playlists", "null");
if (!oldPlaylistsJson.equals("null")){
Type playlistType = new TypeToken<ArrayList<Playlist>>() {}.getType();
LibraryInfo.playlists = gson.fromJson(oldPlaylistsJson, playlistType);
}
else{
LibraryInfo.playlists = new ArrayList<Playlist>();
}
// Load old shuffle status
String shuffleHistory = sharedPrefs.getString("shuffleHistory", "null");
Type intArrayType = new TypeToken<ArrayList<Integer>>() {}.getType();
gson = new Gson();
if(!shuffleHistory.equals("null") ){
CurrentData.shuffleHistory = gson.fromJson(shuffleHistory, intArrayType);
}
String shuffleQueue = sharedPrefs.getString("shuffleQueue", "null");
if(!shuffleQueue.equals("null") ){
Type arrayType = new TypeToken<int[]>() {}.getType();
CurrentData.shuffleQueue = gson.fromJson(shuffleQueue, arrayType);
}
CurrentData.shuffleHistoryPosition = sharedPrefs.getInt("shuffleHistoryPosition", 0);
Intent i = new Intent(LoadingScreenActivity.this, MusicPlayerActivity.class);
startActivity(i);
finish();
}
/**
* Task which scans the SD card for music files and fills in the LibraryInfo class.
*/
private class LoadLibrary extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected Void doInBackground(Void... arg0) {
Log.d("Library", "No Library Loaded");
LibraryFiller libFillAll = new LibraryFiller(getApplicationContext());
libFillAll.loadLibrary();
Gson gson = new Gson();
String songsListJson = gson.toJson(LibraryInfo.songsList);
SharedPreferences.Editor editor = sharedPrefs.edit();
editor.putString("songsList", songsListJson);
editor.commit();
// Look up the directory to search for music from the preferences activity
//Log.d("Library", "No Library Loaded");
//String library_location = sharedPrefs.getString("library_location", "null");
//LibraryFiller libFill = new LibraryFiller(library_location);
//if(libFill.loadLibrary() == -1){
//Toast.makeText(getApplicationContext(), "Invalid Library folder, could not load music.",
//Toast.LENGTH_LONG).show();
// }
// Check if there is a stored playlist; if so, load it, else initialize a new one.
String oldPlaylistJson = sharedPrefs.getString("currentPlaylist", "null");
if (!oldPlaylistJson.equals("null")){
CurrentData.currentPlaylist = gson.fromJson(oldPlaylistJson, Playlist.class);
Log.d("Library", "Playlist Loaded");
}
else{
CurrentData.currentPlaylist = new Playlist();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Close this activity and launch MusicPlayerActivity
Intent i = new Intent(LoadingScreenActivity.this, MusicPlayerActivity.class);
startActivity(i);
finish();
}
这里是logcat：
06-18 11:12:57.923: D/Library(1071): No Library Loaded
06-18 11:12:58.133: W/dalvikvm(1071): threadid=11: thread exiting with uncaught exception (group=0xb2af0ba8)
06-18 11:12:58.193: E/AndroidRuntime(1071): FATAL EXCEPTION: AsyncTask #1
06-18 11:12:58.193: E/AndroidRuntime(1071): Process: com.andrewkiluk.machmusicplayer, PID: 1071
06-18 11:12:58.193: E/AndroidRuntime(1071): java.lang.RuntimeException: An error occured while executing doInBackground()
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.os.AsyncTask$3.done(AsyncTask.java:300)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.util.concurrent.FutureTask.run(FutureTask.java:242)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.lang.Thread.run(Thread.java:841)
06-18 11:12:58.193: E/AndroidRuntime(1071): Caused by: java.lang.SecurityException: Permission Denial: reading com.android.providers.media.MediaProvider uri content://media/external/audio/media from pid=1071, uid=10066 requires android.permission.READ_EXTERNAL_STORAGE, or grantUriPermission()
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.os.Parcel.readException(Parcel.java:1465)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:185)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:137)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.content.ContentProviderProxy.query(ContentProviderNative.java:413)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.content.ContentResolver.query(ContentResolver.java:461)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.content.ContentResolver.query(ContentResolver.java:404)
06-18 11:12:58.193: E/AndroidRuntime(1071): at com.andrewkiluk.machmusicplayer.LibraryFiller.loadSongsListContentResolver(LibraryFiller.java:181)
06-18 11:12:58.193: E/AndroidRuntime(1071): at com.andrewkiluk.machmusicplayer.LibraryFiller.loadLibrary(LibraryFiller.java:74)
06-18 11:12:58.193: E/AndroidRuntime(1071): at com.andrewkiluk.machmusicplayer.LoadingScreenActivity$LoadLibrary.doInBackground(LoadingScreenActivit y.java:127)
06-18 11:12:58.193: E/AndroidRuntime(1071): at com.andrewkiluk.machmusicplayer.LoadingScreenActivity$LoadLibrary.doInBackground(LoadingScreenActivit y.java:1)
06-18 11:12:58.193: E/AndroidRuntime(1071): at android.os.AsyncTask$2.call(AsyncTask.java:288)
06-18 11:12:58.193: E/AndroidRuntime(1071): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
06-18 11:12:58.193: E/AndroidRuntime(1071): ... 4 more
答案 0 :(得分：1)
正如这句话所说：
Caused by: java.lang.SecurityException: Permission Denial: reading com.android.providers.media.MediaProvider uri content://media/external/audio/media from pid=1071, uid=10066 requires android.permission.READ_EXTERNAL_STORAGE, or grantUriPermission()
您需要Android Manifest中的权限android.permission.READ_EXTERNAL_STORAGE。
写下这个：
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />