I once tried to use MediaScanner to resolve problems; however it turned out to be a failure. Now I make it.This post is to write down why I failed and how I work it out now. I think it could be deeper that other posts.
Android Media Scanning Mechanism
Android provides a great application for developers to add created media files to add them into the library. The application is called MediaProvider. Now let’s have a glance of MediaProvider. The receiver part of its manifest
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | <receiver android:name="MediaScannerReceiver"> <intent-filter> <action android:name="android.intent.action.BOOT_COMPLETED" /> </intent-filter> <intent-filter> <action android:name="android.intent.action.MEDIA_MOUNTED" /> <data android:scheme="file" /> </intent-filter> <intent-filter> <action android:name="android.intent.action.MEDIA_UNMOUNTED" /> <data android:scheme="file" /> </intent-filter> <intent-filter> <action android:name="android.intent.action.MEDIA_SCANNER_SCAN_FILE" /> <data android:scheme="file" /> </intent-filter> </receiver> |
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The MediaScannerReceiver will receive the above intents with right action and data scheme.
How the MediaScannerRecieve handles the intent
- It will scan internal storage only after receiving the action android.intent.action.BOOT_COMPLETED
- All intent but the android.intent.action.BOOT_COMPLETED intent should carry the file scheme data
- It will scan external storage when receiving the Intent.ACTION_MEDIA_MOUNTED intent.
- It will scan the single file when receiving the Intent.ACTION_MEDIA_SCANNER_SCAN_FILE intent. How the MediaScannerService works Actually receiver does not do scanning. It will start a service called MediaScannerService. The service part of its manifest
1 2 3 4 5 | <service android:name="MediaScannerService" android:exported="true"> <intent-filter> <action android:name="android.media.IMediaScannerService" /> </intent-filter> </service> |
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scanFile Method
1 2 3 4 5 6 | private Uri scanFile(String path, String mimeType) { String volumeName = MediaProvider.EXTERNAL_VOLUME; openDatabase(volumeName); MediaScanner scanner = createMediaScanner(); return scanner.scanSingleFile(path, volumeName, mimeType); } |
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scan Method
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | private void scan(String[] directories, String volumeName) { // don't sleep while scanning mWakeLock.acquire(); ContentValues values = new ContentValues(); values.put(MediaStore.MEDIA_SCANNER_VOLUME, volumeName); Uri scanUri = getContentResolver().insert(MediaStore.getMediaScannerUri(), values); Uri uri = Uri.parse("file://" directories[0]); 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); sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_FINISHED, uri)); mWakeLock.release(); } |
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Actually the scan code is not really in the MediaScannerService
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | 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; } |
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It’s using the android.media.MediaScanner https://android.googlesource.com/platform/frameworks/base/ /cd92588/media/java/android/media/MediaScanner.java
How To Scan A Created File
Now I am going to introduce two ways to add a created file into the media library.
The Simplest Method
Just send a broadcast, as we have posted above. Just send a broadcast intent to MediaScannerReceiver.
1 2 3 4 | String saveAs = "Your_Created_File_Path" Uri contentUri = Uri.fromFile(new File(saveAs)); Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE,contentUri); getContext().sendBroadcast(mediaScanIntent); |
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The above method maybe has been seen thousands of times. Actually it should work. However I failed and failed in sending broadcast intent. In the following section. I will point out why the sending broadcast not works. Even though you get well on with sending broadcast,it’s strongly recommended to read the Section Why Sending MEDIA_SCANNER_SCAN_FILE broadcast not works.
Use MediaScannerConnection
1 2 3 4 5 6 7 8 9 10 11 | public void mediaScan(File file) { MediaScannerConnection.scanFile(getActivity(), new String[] { file.getAbsolutePath() }, null, new OnScanCompletedListener() { @Override public void onScanCompleted(String path, Uri uri) { Log.v("MediaScanWork", "file " path " was scanned seccessfully: " uri); } }); } |
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the scanFile method is introduced since API 8
Create an instance and call scanFile (String path, String mimeType)
It’s really easy, just read the post http://developer.android.com/reference/android/media/MediaScannerConnection.html
How To Scan Mutiple Files
- Sending Mutiple Intent.ACTION_MEDIA_SCANNER_SCAN_FILE broadcast intents.
- Use the second method by filled the second params with an array of paths.
Why Sending MEDIA_SCANNER_SCAN_FILE broadcast not works
Actually someone may think sending ACTION_MEDIA_SCANNER_SCAN_FILE works on some devices but not on other devices. Actually it’s. Is it a API limit? No, It’s has someting to do with your file path. Take a look at this
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | public void onReceive(Context context, Intent intent) { String action = intent.getAction(); Uri uri = intent.getData(); if (action.equals(Intent.ACTION_BOOT_COMPLETED)) { // scan internal storage scan(context, MediaProvider.INTERNAL_VOLUME); } else { if (uri.getScheme().equals("file")) { // handle intents related to external storage String path = uri.getPath(); String externalStoragePath = Environment.getExternalStorageDirectory().getPath(); Log.d(TAG, "action: " action " path: " path); if (action.equals(Intent.ACTION_MEDIA_MOUNTED)) { // scan whenever any volume is mounted scan(context, MediaProvider.EXTERNAL_VOLUME); } else if (action.equals(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE) && path != null && path.startsWith(externalStoragePath "/")) { scanFile(context, path); } } } } |
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Every part is right except the intent data. I mean the file path. You may hardcode the filepath. This is my example
1 2 3 4 5 6 7 8 9 10 | final String saveAs = "/sdcard/" System.currentTimeMillis() "_add.png"; Uri contentUri = Uri.fromFile(new File(saveAs)); Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE,contentUri); getContext().sendBroadcast(mediaScanIntent); Uri uri = mediaScanIntent.getData(); String path = uri.getPath(); String externalStoragePath = Environment.getExternalStorageDirectory().getPath(); Log.i("LOGTAG", "Androidyue onReceive intent= " mediaScanIntent ";path=" path ";externalStoragePath=" externalStoragePath); |
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And this is the output log
1 | LOGTAG Androidyue onReceive intent= Intent { act=android.intent.action.MEDIA_SCANNER_SCAN_FILE dat=file:///sdcard/1390136305831_add.png };path=/sdcard/1390136305831_add.png;externalStoragePath=/mnt/sdcard |
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So in the sending broadcast, your action is right, your data schema OK, your data path not null;but your path /sdcard/1390136305831_add.png does not startswith the externalStoragePath /mnt/sdcard/ And so the scan file is actually not called. In conclusion your hardcoding path results in the failure.
Remove From Media Library
If we deleted a file ,it means that we need to remove the file from the media library.
Simply sending a broadcast?
Can we simple sending a broadcast to the MediaScannerReceiver? I also wish it could. But actually it does not work. Look at this code for the explanation.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | // 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; } } |
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As the above code points out, It does have a check before the real scanning. Then how should I do?
1 2 3 4 5 6 7 8 | public void testDeleteFile() { String existingFilePath = "/mnt/sdcard/1390116362913_add.png"; File existingFile = new File(existingFilePath); existingFile.delete(); ContentResolver resolver = getActivity().getContentResolver(); resolver.delete(Images.Media.EXTERNAL_CONTENT_URI, Images.Media.DATA "=?", new String[]{existingFilePath}); } |
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The above code works. Just remove from Media Provider
Special
- You could check the external.db or internal.db file under /data/data/com.android.providers.media/ for more detailed information.
Others
- Professional Android 4 Application Development
- Android Hacker’s Handbook
