Android MediaScanner原始碼解析

標籤：android   mediascann   media   

1. 簡介

MediaScanner向上和MediaProvider.MediaScannerService互動, 響應其請求;
向下和JNI互動.
MediaScanner主要工作內容:
（1）接收MediaScannerService的scanDirectories和scanSingleFile請求
（2）擷取各個ContentProvider 環境（Audio，Video，Image，File） initialize
（3）擷取需要掃描檔案清單，移除已刪除檔案資訊 prescan
（4）通過media_jni(android_media_MediaScanner.cpp)調用底層介面處理掃描
（5）接收media_jni處理結果，在android_media_MediaScanner.cpp中儲存一個MyMediaScannerClient用於調用MediaScanner
（6）儲存擷取的檔案資訊 postscan
代碼位置:
frameworks/base/media/java/android/media/MediaScanner.java

2. scanDirectories

scanDirectories(String[] directories, String volumeName)
掃描檔案夾，被MSS調用
MediaScanner處理檔案夾的具體流程是：
在MediaScanner中
核心代碼如下：

    public void scanDirectories(String[] directories, String volumeName) {            ......            initialize(volumeName);            prescan(null, true);            ......            for (int i = 0; i < directories.length; i++) {                processDirectory(directories[i], mClient);            }            ......            postscan(directories);             ......            releaseResources();        }    }

3. initialize

void initialize(String volumeName)
initialize和releaseResources相對應
功能就是初始化各個ContentProvider （Audio，Video，Image，File）

    private void initialize(String volumeName) {        mMediaProvider = mContext.getContentResolver().acquireProvider("media");        mAudioUri = Audio.Media.getContentUri(volumeName);        mVideoUri = Video.Media.getContentUri(volumeName);        mImagesUri = Images.Media.getContentUri(volumeName);        mThumbsUri = Images.Thumbnails.getContentUri(volumeName);        mFilesUri = Files.getContentUri(volumeName);        mFilesUriNoNotify = mFilesUri.buildUpon().appendQueryParameter("nonotify", "1").build();        if (!volumeName.equals("internal")) {            // we only support playlists on external media            mProcessPlaylists = true;            mProcessGenres = true;            mPlaylistsUri = Playlists.getContentUri(volumeName);            mCaseInsensitivePaths = true;        }    }

4. prescan

void prescan(String filePath, boolean prescanFiles)
擷取需要掃描檔案清單，移除已刪除檔案資訊

5. postscan

void postscan(String[] directories)
把擷取的檔案資訊寫回資料庫
其主要工作在
void processPlayLists()
和
void processPlayList(FileEntry entry, Cursor fileList)
完成

5.1 processPlayLists()

    private void processPlayLists() throws RemoteException {        Iterator<FileEntry> iterator = mPlayLists.iterator();        Cursor fileList = null;        try {            // use the files uri and projection because we need the format column,            // but restrict the query to just audio files            fileList = mMediaProvider.query(mPackageName, mFilesUri, FILES_PRESCAN_PROJECTION,                    "media_type=2", null, null, null);            while (iterator.hasNext()) {                FileEntry entry = iterator.next();                // only process playlist files if they are new or have been modified since the last scan                if (entry.mLastModifiedChanged) {                    processPlayList(entry, fileList);                }            }        }    }

5.2 processPlayList(FileEntry entry, Cursor fileList)
processPlayList(FileEntry entry, Cursor fileList)的工作是把資訊寫回資料庫

6. processDirectory

調用native層

private native void processDirectory(String path, MediaScannerClient client);

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Android MediaScanner原始碼解析