SettingsProvider 之 FileObserver

转载请注明出处：http://blog.csdn.net/droyon/article/details/35558637

// FileObserver for external modifications to the database file.    // Note that this is for platform developers only with    // userdebug/eng builds who should be able to tinker with the    // sqlite database out from under the SettingsProvider, which is    // normally the exclusive owner of the database.  But we keep this    // enabled all the time to minimize development-vs-user    // differences in testing.    //FileObserver是外部对数据库修改的监听。    //这是userdebug或者eng版本的平台开发者，开发者也是独占数据库的所有者，能够在SettingsProvider中摆弄sqlite数据库。    //这个监听，能够保持长久运行，减小开发者和用户之间的差距。    private static SparseArray<SettingsFileObserver> sObserverInstances            = new SparseArray<SettingsFileObserver>();    private class SettingsFileObserver extends FileObserver {        private final AtomicBoolean mIsDirty = new AtomicBoolean(false);        private final int mUserHandle;        private final String mPath;        public SettingsFileObserver(int userHandle, String path) {            super(path, FileObserver.CLOSE_WRITE |                  FileObserver.CREATE | FileObserver.DELETE |                  FileObserver.MOVED_TO | FileObserver.MODIFY);            mUserHandle = userHandle;            mPath = path;        }        public void onEvent(int event, String path) {            int modsInFlight = sKnownMutationsInFlight.get(mUserHandle).get();            if (modsInFlight > 0) {                // our own modification.                return;            }            Log.d(TAG, "User " + mUserHandle + " external modification to " + mPath                    + "; event=" + event);            if (!mIsDirty.compareAndSet(false, true)) {//isDirty为true，说明在进行fullyPopulateCaches，不需要在做。                // already handled. (we get a few update events                // during an sqlite write)                return;            }            Log.d(TAG, "User " + mUserHandle + " updating our caches for " + mPath);            fullyPopulateCaches(mUserHandle);            mIsDirty.set(false);        }    }