MediaScanner源码结构学习

* native MyMediaScannerClient scanFile, which calls
* Java MyMediaScannerClient scanFile, which calls
* Java MediaScannerClient doScanFile, which calls
* Java MediaScanner processFile (native method), which calls
scanFile(context, path);//扫描单个文件
}
}
}
}
privatevoidscan(Contextcdontext,Stringvolume){
//启动MediaScannerService，扫描目录
Bundle args = new Bundle();
args.putString("volume",volume);
args.putString("filepath",path);
context.startService(
newIntent(context,MediaScannerService.class).putExtras(args));
}
}
倒是很简洁，其启动了MediaScannerService，打开android4.2/packages/providers/mediaprovider/src/com/android/providers/media/MediaScannerService.java
publicvoidonReceive(Contextcontext,Intentintent){
finalStringaction=intent.getAction();
finalUriuri=intent.getData();
if(Intent.ACTION_BOOT_COMPLETED.equals(action)){
// scan whenever any volume is mounted
// sd卡挂载后扫描，也可以看出，他只扫描external ----> external.db中
scan(context,MediaProvider.EXTERNAL_VOLUME);
}elseif(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE.equals(action)&&
path!=null&&path.startsWith(externalStoragePath+"/")){
//如果是有文件拷贝进入，且路径不为空，且是在第一存储设备上（手机存储有预先制定好的ExternalStorage
//与SecondStorage，并不是说外卡就是externalStorage，内卡就是SecondStorage，我在项目中犯过这个错误理解）
* Java MyMediaScanner handleStringTag.
* Once MediaScanner processFile returns, an entry is inserted in to the database.
*
* The MediaScanner class is not thread-safe, so it should only be used in a single threaded manner.
在看MediaScanner前，先看到MediaScanner.java文件开头处的注释，官方的流程介绍：
/**
* Internal service helper that no-one should use directly.
*
* The way the scan currently works is:
Stringpath=uri.getPath();
StringexternalStoragePath=Environment.getExternalStorageDirectory().getPath();
Log.d(TAG,"action: "+action+" path: "+path);
if(Intent.ACTION_MEDIA_MOUNTED.equals(action)){
*
* {@hide}
*/
MediaScannerReceiver.java文件用于接收系统重启后，已经插拔卡，以及文件复制与拷贝等消息，收到消息后会进行扫描。启动MediaScannerService，进行相关操作，MediaScannerService的主线程接收通知，然后单独启动一个handler去处理消息。
* native MyMediaScannerClient.scanFile() for every file whose extension matches.
* - native MyMediaScannerClient.scanFile() calls back on Java MediaScannerClient.scanFile,
//onCreate 函数
@Override
publicvoidonCreate()
{
PowerManagerpm=(PowerManager)getSystemService(Context.POWER_SERVICE);
mWakeLock=pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,TAG);
MediaScannerReceiver.java文件很简单，先看一下
publicclassMediaScannerReceiverextendsBroadcastReceiver{
privatefinalstaticStringTAG="MediaScannerReceiver";
@Override
scan(context,MediaProvider.INTERNAL_VOLUME);
scan(context,MediaProvider.EXTERNAL_VOLUME);
}else{
if(uri.getScheme().equals("file")){
// handle intents related to external storage
//系统启动完毕后会发送broadcast，MediaScannerReceiver收到消息开始扫描内外存储设备，
//在此，我的理解，internal是存储系统相关的，external存储的是所有的自带存储空间以及外面插入的sd卡等信息
// Scan both internal and external storage
* Java MyMediaScannerClient.endFile(), which takes all the data that's been
* gathered and inserts an entry in to the database.
*
* In summary:
* Java MediaScannerService calls
// 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.
* object (which got created when the Java MediaScanner was created).
* - native MediaScanner.processDirectory() calls
* doProcessDirectory(), which recurses over the folder, and calls
* - the processDirectory() JNI method wraps the provided mediascanner client in a native
* 'MyMediaScannerClient' class, then calls processDirectory() on the native MediaScanner
//获取屏幕常亮，扫描期间不停歇
StorageManagerstorageManager=(StorageManager)getSystemService(Context.STORAGE_SERVICE);
mExternalStoragePaths=storageManager.getVolumePaths();
Threadthr=newThread(null,this,"MediaScannerService");
//新起线程，防止主线程阻塞，其启动run函数
thr.start();
}
publicvoidrun()
* - The Java MediaScannerService creates a MediaScanner (this class), and calls
* MediaScanner.scanDirectories on it.
* - scanDirectories() calls the native processDirectory() for each of the specified directories.