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 ) {
            //[+LEUI][BUG][SI-17406][Guo He][20150630]
            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();
        }
    }

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