Android系统扫描音频文件详解

扫描文件是在MediaScannerService类的ServiceHandler中：

private final class ServiceHandler extends Handler    {        @Override        public void handleMessage(Message msg)        {            Bundle arguments = (Bundle) msg.obj;            String filePath = arguments.getString("filepath");//单个文件            String path = arguments.getString("path");//文件目录            try {                if (filePath != null) {                    IBinder binder = arguments.getIBinder("listener");                    IMediaScannerListener listener =                             (binder == null ? null : IMediaScannerListener.Stub.asInterface(binder));                    Uri uri = null;                    try {                        uri = scanFile(filePath, arguments.getString("mimetype"));//扫描单个文件                    } catch (Exception e) {                        Log.e(TAG, "Exception scanning file", e);                    }                    if (listener != null) {                        listener.scanCompleted(filePath, uri);                    }                } else {                    String volume = arguments.getString("volume");                    String[] directories = null;                    if (MediaProvider.INTERNAL_VOLUME.equals(volume)) {                        // scan internal media storage                        directories = new String[] {                                Environment.getRootDirectory() + "/media",                        };                    }                    else if (MediaProvider.EXTERNAL_VOLUME.equals(volume)) {                        // scan external storage volumes            if (path == null) {                          directories = mExternalStoragePaths;            } else if (path.startsWith("/mnt/usb_storage")) {                directories = new String[] {path};//{"/mnt/usb_storage"};                        } else {                            directories = new String[] {path};            }                    }                    if (directories != null) {                        if (true) Log.d(TAG, "start scanning volume " + volume + ": "                                + Arrays.toString(directories));                        scan(directories, volume);//扫描文件列表                        if (true) Log.d(TAG, "done scanning volume " + volume);                    }                }            } catch (Exception e) {                Log.e(TAG, "Exception in handleMessage", e);            }            stopSelf(msg.arg1);        }    };

最终会调用scan或者scanFile扫描

private void scan(String[] directories, String volumeName) {        Uri uri = Uri.parse("file://" + directories[0]);        // don't sleep while scanning        mWakeLock.acquire();        try {            ContentValues values = new ContentValues();            values.put(MediaStore.MEDIA_SCANNER_VOLUME, volumeName);            Uri scanUri = getContentResolver().insert(MediaStore.getMediaScannerUri(), values);            sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_STARTED, uri));            try {                if (volumeName.equals(MediaProvider.EXTERNAL_VOLUME)) {                    openDatabase(volumeName);                }            MediaScanner scanner = createMediaScanner();        if(directories!=null){              scanner.scanDirectories(directories, volumeName);        }        } catch (Exception e) {            Log.e(TAG, "exception in MediaScanner.scan()", e);        }            getContentResolver().delete(scanUri, null, null);        } finally {            sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_FINISHED, uri));            mWakeLock.release();        }    }private Uri scanFile(String path, String mimeType) {        String volumeName = MediaProvider.EXTERNAL_VOLUME;        openDatabase(volumeName);        MediaScanner scanner = createMediaScanner();        try {            // make sure the file path is in canonical form            String canonicalPath = new File(path).getCanonicalPath();            return scanner.scanSingleFile(canonicalPath, volumeName, mimeType);        } catch (Exception e) {            Log.e(TAG, "bad path " + path + " in scanFile()", e);            return null;        }    }

然后进入MediaScanner实现扫描

// this function is used to scan a single file    public Uri scanSingleFile(String path, String volumeName, String mimeType) {        try {            initialize(volumeName);            prescan(path, true);            File file = new File(path);            if (!file.exists()) {                return null;            }            // lastModified is in milliseconds on Files.            long lastModifiedSeconds = file.lastModified() / 1000;            // always scan the file, so we can return the content://media Uri for existing files            return mClient.doScanFile(path, mimeType, lastModifiedSeconds, file.length(),                    false, true, MediaScanner.isNoMediaPath(path));        } catch (RemoteException e) {            Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e);            return null;        }    }//初始化默认的uriprivate void initialize(String volumeName) {        mMediaProvider = mContext.getContentResolver().acquireProvider("media");        mAudioUri = Audio.Media.getContentUri(volumeName);        mVideoUri = Video.Media.getContentUri(volumeName);        mImagesUri = Images.Media.getContentUri(volumeName);        mThumbsUri = Images.Thumbnails.getContentUri(volumeName);        mFilesUri = Files.getContentUri(volumeName);        mFilesUriNoNotify = mFilesUri.buildUpon().appendQueryParameter("nonotify", "1").build();        if (!volumeName.equals("internal")) {            // we only support playlists on external media            mProcessPlaylists = true;            mProcessGenres = true;            mPlaylistsUri = Playlists.getContentUri(volumeName);            mCaseInsensitivePaths = true;        }    }//扫描预处理，暂时不知道做什么用private void prescan(String filePath, boolean prescanFiles) throws RemoteException {        Cursor c = null;        String where = null;        String[] selectionArgs = null;        if (mPlayLists == null) {            mPlayLists = new ArrayList<FileEntry>();        } else {            mPlayLists.clear();        }        if (filePath != null) {            // query for only one file            where = MediaStore.Files.FileColumns._ID + ">?" +                " AND " + Files.FileColumns.DATA + " like '"+filePath+"%' ";            selectionArgs = new String[] { "" };        } else {            where = MediaStore.Files.FileColumns._ID + ">?";            selectionArgs = new String[] { "" };        }        if (DEBUG_MEDIASCANNER)            Log.d(TAG,"-----------enter prescan,filePath = "+filePath+"where = "+where);        // Tell the provider to not delete the file.        // If the file is truly gone the delete is unnecessary, and we want to avoid        // accidentally deleting files that are really there (this may happen if the        // filesystem is mounted and unmounted while the scanner is running).        Uri.Builder builder = mFilesUri.buildUpon();        builder.appendQueryParameter(MediaStore.PARAM_DELETE_DATA, "false");        MediaBulkDeleter deleter = new MediaBulkDeleter(mMediaProvider, mPackageName,                builder.build());        // Build the list of files from the content provider        try {            if (prescanFiles) {                // First read existing files from the files table.                // Because we'll be deleting entries for missing files as we go,                // we need to query the database in small batches, to avoid problems                // with CursorWindow positioning.                long lastId = Long.MIN_VALUE;                Uri limitUri = mFilesUri.buildUpon().appendQueryParameter("limit", "1000").build();                mWasEmptyPriorToScan = true;                while (true) {                    selectionArgs[0] = "" + lastId;                    if (c != null) {                        c.close();                        c = null;                    }                    c = mMediaProvider.query(mPackageName, limitUri, FILES_PRESCAN_PROJECTION,                            where, selectionArgs, MediaStore.Files.FileColumns._ID, null);                    if (c == null) {                        break;                    }                    int num = c.getCount();                    if (num == 0) {                        break;                    }                    mWasEmptyPriorToScan = false;                    while (c.moveToNext()) {                        long rowId = c.getLong(FILES_PRESCAN_ID_COLUMN_INDEX);                        String path = c.getString(FILES_PRESCAN_PATH_COLUMN_INDEX);                        int format = c.getInt(FILES_PRESCAN_FORMAT_COLUMN_INDEX);                        long lastModified = c.getLong(FILES_PRESCAN_DATE_MODIFIED_COLUMN_INDEX);                        lastId = rowId;                        // Only consider entries with absolute path names.                        // This allows storing URIs in the database without the                        // media scanner removing them.                        if (path != null && path.startsWith("/")) {                            boolean exists = false;                            try {                                exists = Libcore.os.access(path, libcore.io.OsConstants.F_OK);                            } catch (ErrnoException e1) {                            }                            if (!exists && !MtpConstants.isAbstractObject(format)) {                                // do not delete missing playlists, since they may have been                                // modified by the user.                                // The user can delete them in the media player instead.                                // instead, clear the path and lastModified fields in the row                                MediaFile.MediaFileType mediaFileType = MediaFile.getFileType(path);                                int fileType = (mediaFileType == null ? 0 : mediaFileType.fileType);                                if (!MediaFile.isPlayListFileType(fileType)) {                                    deleter.delete(rowId);                                    if (path.toLowerCase(Locale.US).endsWith("/.nomedia")) {                                        deleter.flush();                                        String parent = new File(path).getParent();                                        mMediaProvider.call(mPackageName, MediaStore.UNHIDE_CALL,                                                parent, null);                                    }                                }                            }                        }                    }                }            }        }        finally {            if (c != null) {                c.close();            }            deleter.flush();        }        // compute original size of images        mOriginalCount = 0;        c = mMediaProvider.query(mPackageName, mImagesUri, ID_PROJECTION, null, null, null, null);        if (c != null) {            mOriginalCount = c.getCount();            c.close();        }    }

下面是真正的扫描实现

public Uri doScanFile(String path, String mimeType, long lastModified,                long fileSize, boolean isDirectory, boolean scanAlways, boolean noMedia) {            Uri result = null;//            long t1 = System.currentTimeMillis();            try {                FileEntry entry = beginFile(path, mimeType, lastModified,                        fileSize, isDirectory, noMedia);                if (path.startsWith("/mnt/usb_storage"))                    mIsUsbStorage =true;                else                    mIsUsbStorage =false;                // if this file was just inserted via mtp, set the rowid to zero                // (even though it already exists in the database), to trigger                // the correct code path for updating its entry                if (mMtpObjectHandle != 0) {                    entry.mRowId = 0;                }                // rescan for metadata if file was modified since last scan                if (entry != null && (entry.mLastModifiedChanged || scanAlways)) {                    if (noMedia) {                        result = endFile(entry, false, false, false, false, false);                    } else {                        String lowpath = path.toLowerCase(Locale.ROOT);                        boolean ringtones = (lowpath.indexOf(RINGTONES_DIR) > 0);                        boolean notifications = (lowpath.indexOf(NOTIFICATIONS_DIR) > 0);                        boolean alarms = (lowpath.indexOf(ALARMS_DIR) > 0);                        boolean podcasts = (lowpath.indexOf(PODCAST_DIR) > 0);                        boolean music = (lowpath.indexOf(MUSIC_DIR) > 0) ||                            (!ringtones && !notifications && !alarms && !podcasts);//判断是否是音视频格式，来决定下面是否对其扫描。 boolean isaudio = MediaFile.isAudioFileType(mFileType); boolean isvideo = MediaFile.isVideoFileType(mFileType); boolean isimage = MediaFile.isImageFileType(mFileType); if (isaudio || isvideo || isimage) {                            if (mExternalIsEmulated && path.startsWith(mExternalStoragePath)) {  // try to rewrite the path to bypass the sd card fuse layer String directPath = Environment.getMediaStorageDirectory() +                                 path.substring(mExternalStoragePath.length());       File f = new File(directPath);   if (f.exists()) {                   path = directPath;                      }               }       } // we only extract metadata for audio and video files    if (isaudio /*|| isvideo */)            {             //jni方法调用，真正的扫描开始             processFile(path, mimeType, this);             }   //if (isimage) {      //    processImageFile(path);//}  result = endFile(entry, ringtones, notifications, alarms, music, podcasts);                    }                }            } catch (RemoteException e) {                Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e);            }//            long t2 = System.currentTimeMillis();//            Log.v(TAG, "scanFile: " + path + " took " + (t2-t1));            return result;        }