1. 简介

MediaScannerService简称MSS, 是一个运行于后台的Service, 实现了Runnable接口.
MediaScannerReceiver接收广播, 然后由MSS具体完成工作. MSS中主要工作在ServiceHandler实现

2. 初始化

2.1 onCreate()

完成2项工作
(1)启动线程

        // Start up the thread running the service.  Note that we create a        // separate thread because the service normally runs in the process's        // main thread, which we don't want to block.        Thread thr = new Thread(null, this, "MediaScannerService");        thr.start();

之后会调用run方法, 参见2.2
(2) 注册/监听SDCard 卸载事件

        IntentFilter filter = new IntentFilter(Intent.ACTION_MEDIA_EJECT);        filter.addDataScheme("file");        filter.setPriority(100);        registerReceiver(mUnmountReceiver, filter);

2.2 run

MSS实现Runable的run方法, onCreate时会调用此方法启动线程.
run方法主要功能就是启动ServiceHandler

    public void run()    {        Looper.prepare();        mServiceLooper = Looper.myLooper();        mServiceHandler = new ServiceHandler();        /// M: reduce thread priority after ServiceHandler have been created to avoid cpu starvation        /// which may cause ANR because create service handler too slow.        // reduce priority below other background threads to avoid interfering        // with other services at boot time.        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND + Process.THREAD_PRIORITY_LESS_FAVORABLE);        Looper.loop();    }

2.3 onStartCommand

(1) 等待ServiceHandler启动

        while (mServiceHandler == null) {            synchronized (this) {                try {                    wait(100);                } catch (InterruptedException e) {                    MtkLog.e(TAG, "onStartCommand: InterruptedException!");                }            }        }

(2) 处理Intent消息

        Bundle arguments = intent.getExtras();        int what;        if (arguments.getString("filepath") != null) {            what = MSG_SCAN_SINGLE_FILE;        } else if ( arguments.getString( "thumbPath" ) != null ) {            Log.d( TAG, "get do extract thumb action " );            what = MSG_EXTRACT_THUMBNAILS;        } else {            what = MSG_SCAN_DIRECTORY;        }

(3) 把消息传给ServiceHandler

        Message msg = mServiceHandler.obtainMessage(what, startId, -1, arguments);        mServiceHandler.sendMessage(msg);

2.4 onBind

    @Override    public IBinder onBind(Intent intent)    {        return mBinder;    }    private final IMediaScannerService.Stub mBinder =             new IMediaScannerService.Stub() {        public void requestScanFile(String path, String mimeType, IMediaScannerListener listener)        {            if (false) {                Log.d(TAG, "IMediaScannerService.scanFile: " + path + " mimeType: " + mimeType);            }            Bundle args = new Bundle();            args.putString("filepath", path);            args.putString("mimetype", mimeType);            if (listener != null) {                args.putIBinder("listener", listener.asBinder());            }            startService(new Intent(MediaScannerService.this,                    MediaScannerService.class).putExtras(args));        }        public void scanFile(String path, String mimeType) {            requestScanFile(path, mimeType, null);        }    };

3. ServiceHandler

处理2中类型
文件夹:
scan(directories, volume);
文件:
uri = scanFile(filePath, arguments.getString(“mimetype”));

private final class ServiceHandler extends Handler    {        @Override        public void handleMessage(Message msg)        {            Bundle arguments = (Bundle) msg.obj;            String filePath = arguments.getString("filepath");            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"));                    } 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",                                Environment.getOemDirectory() + "/media",                        };                    }                    else if (MediaProvider.EXTERNAL_VOLUME.equals(volume)) {                        // scan external storage volumes                        directories = mExternalStoragePaths;                    }                    if (directories != null) {                        if (false) Log.d(TAG, "start scanning volume " + volume + ": "                                + Arrays.toString(directories));                        scan(directories, volume);                        if (false) Log.d(TAG, "done scanning volume " + volume);                    }                }            } catch (Exception e) {                Log.e(TAG, "Exception in handleMessage", e);            }            stopSelf(msg.arg1);        }    };}

4. scanFile & scan

scanFile 和scan 逻辑上基本相同, 都是调用framworks/base/media/java/android/media/MediaScanner.java完成具体工作

4.1 createMediaScanner

framworks/base/media/java/android/media/MediaScanner.java

    private MediaScanner createMediaScanner() {        MediaScanner scanner = new MediaScanner(this);        Locale locale = getResources().getConfiguration().locale;        if (locale != null) {            String language = locale.getLanguage();            String country = locale.getCountry();            String localeString = null;            if (language != null) {                if (country != null) {                    scanner.setLocale(language + "_" + country);                } else {                    scanner.setLocale(language);                }            }            }        return scanner;    }

4.2 scanFile

核心:
scanner.scanSingleFile(canonicalPath, volumeName, mimeType);

    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;        }    }

4.3 scan

核心语句
scanner.scanDirectories(directories, volumeName);

    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();                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();        }    }

Android(安卓)MediaScannerService源码分析