code小生,一个专注 Android 领域的技术分享平台
作者：kkyflying
地址：https://juejin.im/post/5b23744e6fb9a00e315c18e1
声明：本文来自 kkyflying 投稿,转发等请联系原作者授权
前言
如果你不知道RK是啥玩意,请先google或者baidu (:з」∠)
环境
RK3368
Android 6.0.1
需要解决的问题
当设备接入U盘的后,RK全家桶都读不到U盘里的多媒体的资源,例如:mp4,mp3之类的.
(不幸的是,这个功能是客户的刚需.)
解决方案
分析过程
1. 虽然RK全家桶都没有读到U盘里的数据,但是在文件夹管理器上却可以看到挂载上去的U盘,点击进去也能看到U盘里的资料,当时是判断为可能RK全家桶有点问题,回头就去下载了RK的RockVideoPlayer源码来分析.
2. 在RockVideoPlayer.java下就能看到这个播放器的基本原理了,在onCreate中调用了initLoader()
public void initLoader() {
int hasWriteContactsPermission = checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE);
if (hasWriteContactsPermission != PackageManager.PERMISSION_GRANTED) {
requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
REQUEST_CODE_ASK_PERMISSIONS);
return;
}
getLoaderManager().initLoader(0, null, this);
}
再看看
public class RockVideoPlayer extends Activity implements View.OnCreateContextMenuListener,DBUtils.Def,LoaderManager.LoaderCallbacks<Cursor>{}
基本就确定是用Android的CursorLoader来获得各种多媒体资源,CursorLoader也是有点小坑,以前我写过图片管理器也是用这个实现的.
再看看LoaderManager.LoaderCallbacks 这个接口的实现
@Override
public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) {
// TODO Auto-generated method stub
LOG("<-------------- onCreateLoader-------------->");
mSortOrder = MediaStore.Video.Media._ID;
StringBuilder where = new StringBuilder();
where.append(MediaStore.Video.Media._ID + " != ''");
where.append(" AND " + MediaStore.Video.Media.MIME_TYPE + " NOT LIKE 'audio%'");
Log.i("kky", "onCreateLoader: "+ where.toString());
Log.i("kky", "onCreateLoader: "+ MediaStore.Video.Media.EXTERNAL_CONTENT_URI);
return new CursorLoader(RockVideoPlayer.this, MediaStore.Video.Media.EXTERNAL_CONTENT_URI, PROJECT, where.toString(), null, mSortOrder);
}
@Override
public void onLoadFinished(Loader<Cursor> arg0, Cursor arg1) {
if(arg1 == null || arg1.getCount() == 0){
toastNoVideo();
}
if(arg1 != null){
cursorLoader = true;
mVideoListAdapter.swapCursor(arg1);
}else{
cursorLoader = false;
}
//getLoaderManager().getLoader(0).stopLoading();
}
@Override
public void onLoaderReset(Loader<Cursor> arg0) {
mVideoListAdapter.swapCursor(null);
}
在onCreateLoader下查询并且返回CursorLoader,在onLoadFinished中,把Cursor加载进adapter中,这一套逻辑看起来并没有任何问题.而且我很早以前也写过图片管理器,和这个的原理逻辑基本上一样.
3. 这个时候我已经怀疑不是RK全家桶的锅了,进adb看的话,能看到挂载路径.
/mnt/media_rw/BC06-A913
在这里看到U盘的全部文件,而且find一下U盘的文件,能发现以下路径下也能找到,证明驱动那边应该是没问题的,已经挂载上了,锅可能就在framework里了
/storage/BC06-A913/
讲道理这个U盘也已经挂上去了,可播放器还是一样读不到,而CursorLoader其实就设置的查询条件去查数据库的数据,最终是调用ContentProvider的query方法进行查询,因此怀疑是数据库没有更新(这个坑我踩过),因此我发送广播进行强制刷新一下其中的一个视频文件.
/**
* 通知媒体库更新文件
*
* @param context
* @param filePath 文件全路径
*/
public static void scanFile(Context context, String filePath) {
filePath = "/storage/BC06-A913/21.mp4";
Intent scanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
scanIntent.setData(Uri.fromFile(new File(filePath)));
context.sendBroadcast(scanIntent);
}
但是结果还是一样,播放器中找不到文件.
4. 去看看这个路径下的文件 ./packages/providers/MediaProvider 因为播放器是用CursorLoader实现的,那么找providers下的MediaProvider来看看,如果锅在framework的话,这里的可能性就很大了,在 /src/com/android/providers/media 下的 MediaScannerReceiver.java 能搜索到对 Intent.ACTION_MEDIA_SCANNER_SCAN_FILE的处理.
在对这个MediaScannerReceiver.java文件的分析,这个是一个Receiver,在onReceive方法里,可以看到一个很明显的rk的改动(我特意去看了AOSP的代码作为对比)
if(("true".equals(SystemProperties.get("ro.udisk.visible")))){
String id = intent.getStringExtra(VolumeInfo.EXTRA_VOLUME_ID);
int state = intent.getIntExtra(VolumeInfo.EXTRA_VOLUME_STATE,-1);
if(VolumeInfo.STATE_MOUNTED == state){
Log.d(TAG,"----MediaScanner get volume mounted,start scan--- state : " + state);
/*StorageManager mStorageManager = context.getSystemService(StorageManager.class);
VolumeInfo vol = mStorageManager.findVolumeById(id);
scanFile(context, vol.getPath().getPath());*/
scan(context, MediaProvider.EXTERNAL_VOLUME);
}
}
看到这里就基本上知道读不到U盘的原因了,必须要配置ro.udisk.visible=true
解决方案
为了验证结论,直接进入adb修改 /system/build.prop 文件,添加上 ro.udisk.visible=true ,再reboot.
然后完成重启后进入播放器就能读到U盘中的数据了.但是这个样只是临时修改,要新生产的固件也能使用的话,需要添加 ./device/rockchip/common/device.mk 上添加,然后重新编译打包即可.
(PS:这里感谢一下RK那边的老哥们的指点,和他们交流下也能学到不少.)
问题解决了,现在要研究一下原理的东西了
Android usb MediaProvider 原理分析
关键的东西还是在 ./packages/providers/MediaProvider 下.
public class MediaScannerReceiver extends BroadcastReceiver {}
public class MediaScannerService extends Service implements Runnable{}
1. MediaScannerReceiver负责接受广播,接受一些U盘的路径之类的信息,在开机完成后,系统发了 Intent.ACTION_BOOT_COMPLETED ,
而MediaScannerReceiver过滤到这个action后就会扫描内部和外部储存.
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
final Uri uri = intent.getData();
if (Intent.ACTION_BOOT_COMPLETED.equals(action)) {
// Scan both internal and external storage
scan(context, MediaProvider.INTERNAL_VOLUME);
scan(context, MediaProvider.EXTERNAL_VOLUME);
Log.d(TAG,action);
}
//....还有一部分,分开解释
}
2. 这里rk添加了一个配置其实为了可以在配置文件上修改,可以简单开关此功能,原理是这里拦截的action是指卷的状态改变,就是U盘的插拔..
if((VolumeInfo.ACTION_VOLUME_STATE_CHANGED.equals(action))){
if(("true".equals(SystemProperties.get("ro.udisk.visible")))){
String id = intent.getStringExtra(VolumeInfo.EXTRA_VOLUME_ID);
int state = intent.getIntExtra(VolumeInfo.EXTRA_VOLUME_STATE,-1);
if(VolumeInfo.STATE_MOUNTED == state){
Log.d(TAG,"----MediaScanner get volume mounted,start scan--- state : " + state);
/*StorageManager mStorageManager = context.getSystemService(StorageManager.class);
VolumeInfo vol = mStorageManager.findVolumeById(id);
scanFile(context, vol.getPath().getPath());*/
scan(context, MediaProvider.EXTERNAL_VOLUME);
}
}
3. 这里就是我上文说的,接受发送过来的信息来刷新数据库,可以看到使用了同一个action, Intent.ACTION_MEDIA_SCANNER_SCAN_FILE
if (uri != null && uri.getScheme() != null && uri.getScheme().equals("file")) {
// handle intents related to external storage
String path = uri.getPath();
String externalStoragePath = Environment.getExternalStorageDirectory().getPath();
String legacyPath = Environment.getLegacyExternalStorageDirectory().getPath();
try {
path = new File(path).getCanonicalPath();
Log.d(TAG,"File(path).getCanonicalPath() : "+path);
} catch (IOException e) {
Log.e(TAG, "couldn't canonicalize " + path);
return;
}
if (path.startsWith(legacyPath)) {
path = externalStoragePath + path.substring(legacyPath.length());
Log.d(TAG,"path.startsWith : "+path);
}
String packageName = intent.getStringExtra("package");
Log.d(TAG, "action: " + action + " path: " + path + " externalStoragePath:"+externalStoragePath);
if (Intent.ACTION_MEDIA_MOUNTED.equals(action)) {
// scan whenever any volume is mounted
scan(context, MediaProvider.EXTERNAL_VOLUME);
} else if (Intent.ACTION_MEDIA_SCANNER_SCAN_FILE.equals(action) &&
path != null && path.startsWith(externalStoragePath + "/")) {
scanFile(context, path);
} else if ( Intent.ACTION_MEDIA_SCANNER_SCAN_FILE.equals(action) &&
"RockExplorer".equals(packageName)) {
scan(context, MediaProvider.INTERNAL_VOLUME);
scan(context, MediaProvider.EXTERNAL_VOLUME);
}
}
4. 而下面这个两个方法才是去启动扫描文件,上面那些都是接受信息和处理逻辑,又看到这两个方法其实是启动了一个Service,所以真正扫描处理是在MediaScannerService.java中.
private void scan(Context context, String volume) {
Log.d(TAG, "volume: " + volume);
Bundle args = new Bundle();
args.putString("volume", volume);
context.startService(
new Intent(context, MediaScannerService.class).putExtras(args));
}
private void scanFile(Context context, String path) {
Log.d(TAG, "filepath: " + path);
Bundle args = new Bundle();
args.putString("filepath", path);
context.startService(
new Intent(context, MediaScannerService.class).putExtras(args));
}
5. MediaScannerService也就一个Service,按照生命周期去看,就做了一些初始化,注意这里开了新的线程,毕竟扫描是耗时的,而Service其实是在main中的.
@Override
public void onCreate()
{
PowerManager pm = (PowerManager)getSystemService(Context.POWER_SERVICE);
mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG);
StorageManager storageManager = (StorageManager)getSystemService(Context.STORAGE_SERVICE);
mExternalStoragePaths = storageManager.getVolumePaths();
// 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();
}
6. 到onStartCommand下的写法我觉得这就很骚了…一直在等待mServiceHandler的完成new(这里我也特意去对比AOSP的代码,原生的也是这样写…),而且在判断intent是否为空,空的话返回Service.START_NOT_STICKY,这样这个Service被kill后就不会restart了,执行到最后返回Service.START_REDELIVER_INTENT,如果Service被kill了,那么系统会把之前的Intent再次发送给Service,直到Service完成处理.(细节处理好评)
@Override
public int onStartCommand(Intent intent, int flags, int startId)
{
while (mServiceHandler == null) {
synchronized (this) {
try {
wait(100);
} catch (InterruptedException e) {
}
}
}
if (intent == null) {
Log.e(TAG, "Intent is null in onStartCommand: ",
new NullPointerException());
return Service.START_NOT_STICKY;
}
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent.getExtras();
Log.d(TAG, "msg.arg1 : "+ startId+" msg.obj : " + msg.obj);
mServiceHandler.sendMessage(msg);
// Try again later if we are killed before we can finish scanning.
return Service.START_REDELIVER_INTENT;
}
7. 看到这里就直到上文的mServiceHandler一直在等待new吧,毕竟不能确定是先执行到onStartCommand,还是在线程中的mServiceHandler先new,看到这里就能发现,处理扫描的任务应该都是在这个ServiceHandler中了.
public void run(){
// 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.prepare();
mServiceLooper = Looper.myLooper();
mServiceHandler = new ServiceHandler();
Looper.loop();
}
8. 在ServiceHandler中就是一堆逻辑处理后调用了scanFile和scan两个方法,上文就说了CursorLoader最后也是调用ContentProvider的query方法进行查询,那ContentProvider的数据哪里来?就是这个在scanFile里调用openDatabase了然后getContentResolver().insert().
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;
}
}
private void openDatabase(String volumeName) {
try {
ContentValues values = new ContentValues();
values.put("name", volumeName);
getContentResolver().insert(Uri.parse("content://media/"), values);
} catch (IllegalArgumentException ex) {
Log.w(TAG, "failed to open media database");
}
}
在scan下用WakeLock.acquire()锁住不让进入休眠,告知系统开始扫描这个路径下的文件,getContentResolver().insert插入数据,完成扫描再告诉系统扫描完成,mWakeLock.release()释放WakeLock,可以进入休眠
private void scan(String[] directories, String volumeName) {
Uri uri = Uri.parse("file://" + directories[0]);
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();
}
}
总结
原理 : 插入U盘后MediaScannerReceiver接受到系统发出的action后,启动MediaScannerService去进行扫描文件,把数据插入到ContentProvider,通过ContentResolver来进行操作,然后在播放器中用CursorLoader来读取.
github链接
https://kkyflying.github.io/android/framework/2018/06/12/RK-Android-Usb.html