[Android Pro] StorageManager简介

StorageManager

StorageManager is the interface to the systems storage service. The storage manager handles storage-related items such as Opaque Binary Blobs (OBBs).

OBBs contain a filesystem that maybe be encrypted on disk and mounted on-demand from an application. OBBs are a good way of providing large amounts of binary assets without packaging them into APKs as they may be multiple gigabytes in size. However, due to their size, they're most likely stored in a shared storage pool accessible from all programs. The system does not guarantee the security of the OBB file itself: if any program modifies the OBB, there is no guarantee that a read from that OBB will produce the expected output.

Get an instance of this class by calling getSystemService(java.lang.String) with an argument of STORAGE_SERVICE. 

从Android 2.3开始新增了一个OBB文件系统和StorageManager类用来管理外部存储上的数据安全。

如果我们设计一款资源包含比较多的游戏，可能你会发现最终生成的APK文件可能高达300MB，但是APK文件很大导致Android系统无法正常安装，而这么大其实都是游戏中用到的资源文件，我们放到SD卡上可能其他应用也可以访问，比如说系统的图片管理器会索引游戏中的图片资源，而音乐播放器也会索引资源中的音乐，所以Android 2.3的OBB文件(Opaque Binary Blob)可以很好的解决大文件在SD卡上分离出APK文件，同时别的程序没有权限访问这样一种隔离的文件系统。
　　android.os.storage.StorageManager类的实例化方法需要使用 getSystemService(Contxt.STORAGE_SERVICE)才可以，eoe再次提醒这是一个API Level至少为9才能调用的类，注意SDK版本以及目标设备的固件。

我们知道android上一般都有外置的存储卡, 
但是通过Environment.getExternalStorageDirectory()获取的是内置的存储卡位置 (也有的手机可以在系统中修改默认存储) 那么如何获取外置存储卡的位置呢? 

通过StorageManager来获取多个sdcard，比使用cat /proc/mounts要好：

public static String[] getStoragePaths(Context cxt) {
        List<String> pathsList = new ArrayList<String>();
        if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.GINGERBREAD) {
            StringBuilder sb = new StringBuilder();
            try {
                pathsList.addAll(new SdCardFetcher().getStoragePaths(new FileReader("/proc/mounts"), sb));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
                File externalFolder = Environment.getExternalStorageDirectory();
                if (externalFolder != null) {
                    pathsList.add(externalFolder.getAbsolutePath());
                }
            }
        } else {
            StorageManager storageManager = (StorageManager) cxt.getSystemService(Context.STORAGE_SERVICE);
            try {
                Method method = StorageManager.class.getDeclaredMethod("getVolumePaths");
                method.setAccessible(true);
                Object result = method.invoke(storageManager);
                if (result != null && result instanceof String[]) {
                    String[] pathes = (String[]) result;
                    StatFs statFs;
                    for (String path : pathes) {
                        if (!TextUtils.isEmpty(path) && new File(path).exists()) {
                            statFs = new StatFs(path);
                            if (statFs.getBlockCount() * statFs.getBlockSize() != 0) {
                                pathsList.add(path);
                            }
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
                File externalFolder = Environment.getExternalStorageDirectory();
                if (externalFolder != null) {
                    pathsList.add(externalFolder.getAbsolutePath());
                }
            }
        }
        return pathsList.toArray(new String[pathsList.size()]);
    }