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Android Reference

MediaScanner


android.media

Class MediaScanner



  • public class MediaScanner
    extends Object
    Internal service helper that no-one should use directly. The way the scan currently works is: - 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. - the processDirectory() JNI method wraps the provided mediascanner client in a native 'MyMediaScannerClient' class, then calls processDirectory() on the native MediaScanner object (which got created when the Java MediaScanner was created). - native MediaScanner.processDirectory() calls doProcessDirectory(), which recurses over the folder, and calls native MyMediaScannerClient.scanFile() for every file whose extension matches. - native MyMediaScannerClient.scanFile() calls back on Java MediaScannerClient.scanFile, which calls doScanFile, which after some setup calls back down to native code, calling MediaScanner.processFile(). - MediaScanner.processFile() calls one of several methods, depending on the type of the file: parseMP3, parseMP4, parseMidi, parseOgg or parseWMA. - each of these methods gets metadata key/value pairs from the file, and repeatedly calls native MyMediaScannerClient.handleStringTag, which calls back up to its Java counterparts in this file. - Java handleStringTag() gathers the key/value pairs that it's interested in. - once processFile returns and we're back in Java code in doScanFile(), it calls 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 Java MediaScanner scanDirectories, which calls Java MediaScanner processDirectory (native method), which calls native MediaScanner processDirectory, which calls native MyMediaScannerClient scanFile, which calls Java MyMediaScannerClient scanFile, which calls Java MediaScannerClient doScanFile, which calls Java MediaScanner processFile (native method), which calls native MediaScanner processFile, which calls native parseMP3, parseMP4, parseMidi, parseOgg or parseWMA, which calls native MyMediaScanner handleStringTag, which calls 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.
    • Constructor Detail

      • MediaScanner

        public MediaScanner(Context c)
    • Method Detail

      • scanDirectories

        public void scanDirectories(String[] directories,
                           String volumeName)
      • isNoMediaPath

        public static boolean isNoMediaPath(String path)
      • scanMtpFile

        public void scanMtpFile(String path,
                       String volumeName,
                       int objectHandle,
                       int format)
      • setLocale

        public void setLocale(String locale)
      • release

        public void release()
        Releases resources associated with this MediaScanner object. It is considered good practice to call this method when one is done using the MediaScanner object. After this method is called, the MediaScanner object can no longer be used.
      • finalize

        protected void finalize()
        Description copied from class: Object
        Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

        Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

        If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

        Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

        Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.

        Overrides:
        finalize in class Object


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