android - 在 Android 中获取外部 SDCard 位置

Question

我有一个应用程序，其 SD 卡中预存了大量数据。

我们支持所有 ICS 之后 的平板电脑。我无法找到在所有设备上正确访问 SDCard 位置的方法。

我查看了此处给出的各种解决方案，但它们似乎并非在所有情况下都有效。寻找通用解决方案。

就算有人能告诉我所有可能的SDCard挂载点

只有在可以缩小解决方案范围的情况下，我才会针对 android 平板电脑。

Answer 1

不幸的是，由于 Android 设备高度分散，这是一个常见问题。 Environment.getExternalStorageDirectory() 指的是设备制造商认为是“外部存储”的任何内容。在某些设备上，这是可移动媒体，如 SD 卡。在某些设备上，这是设备闪存的一部分。( http://developer.android.com/reference/android/os/Environment.html#getExternalStorageDirectory() ) 此处，“外部存储”是指“安装在主机上时可通过 USB 大容量存储模式访问的驱动器”。如果设备制造商选择将外部存储器设置为板载闪存并且还有 SD 卡，则您需要联系该制造商以确定您是否可以使用 SD 卡。对于大多数符合标准的 android 设备(来自谷歌合规列表的已知设备)，Environment.getExternalStorageDirectory() 应该可以工作。或者您可以编写一个自定义存储类来查看挂载点并为您提供到已挂载 SDCard 的正确路径。这是我已经实现的，到目前为止它一直有效。

public class StorageOptions {
    private static ArrayList<String> mMounts = new ArrayList<String>();
    private static ArrayList<String> mVold = new ArrayList<String>();

    public static String[] labels;
    public static String[] paths;
    public static int count = 0;
    private static final String TAG = StorageOptions.class.getSimpleName();

    public static void determineStorageOptions() {
        readMountsFile();

        readVoldFile();

        compareMountsWithVold();

        testAndCleanMountsList();

        setProperties();
    }

    private static void readMountsFile() {
        /*
         * Scan the /proc/mounts file and look for lines like this:
         * /dev/block/vold/179:1 /mnt/sdcard vfat
         * rw,dirsync,nosuid,nodev,noexec,
         * relatime,uid=1000,gid=1015,fmask=0602,dmask
         * =0602,allow_utime=0020,codepage
         * =cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
         * 
         * When one is found, split it into its elements and then pull out the
         * path to the that mount point and add it to the arraylist
         */

        // some mount files don't list the default
        // path first, so we add it here to
        // ensure that it is first in our list
        mMounts.add("/mnt/sdcard");

        try {
            Scanner scanner = new Scanner(new File("/proc/mounts"));
            while (scanner.hasNext()) {
                String line = scanner.nextLine();
                if (line.startsWith("/dev/block/vold/")) {
                    String[] lineElements = line.split(" ");
                    String element = lineElements[1];

                    // don't add the default mount path
                    // it's already in the list.
                    if (!element.equals("/mnt/sdcard"))
                        mMounts.add(element);
                }
            }
        } catch (Exception e) {
            // Auto-generated catch block

            e.printStackTrace();
        }
    }

    private static void readVoldFile() {
        /*
         * Scan the /system/etc/vold.fstab file and look for lines like this:
         * dev_mount sdcard /mnt/sdcard 1
         * /devices/platform/s3c-sdhci.0/mmc_host/mmc0
         * 
         * When one is found, split it into its elements and then pull out the
         * path to the that mount point and add it to the arraylist
         */

        // some devices are missing the vold file entirely
        // so we add a path here to make sure the list always
        // includes the path to the first sdcard, whether real
        // or emulated.
        mVold.add("/mnt/sdcard");

        try {
            Scanner scanner = new Scanner(new File("/system/etc/vold.fstab"));
            while (scanner.hasNext()) {
                String line = scanner.nextLine();
                if (line.startsWith("dev_mount")) {
                    String[] lineElements = line.split(" ");
                    String element = lineElements[2];

                    if (element.contains(":"))
                        element = element.substring(0, element.indexOf(":"));

                    // don't add the default vold path
                    // it's already in the list.
                    if (!element.equals("/mnt/sdcard"))
                        mVold.add(element);
                }
            }
        } catch (Exception e) {
            // Auto-generated catch block

            e.printStackTrace();
        }
    }

    private static void compareMountsWithVold() {
        /*
         * Sometimes the two lists of mount points will be different. We only
         * want those mount points that are in both list.
         * 
         * Compare the two lists together and remove items that are not in both
         * lists.
         */

        for (int i = 0; i < mMounts.size(); i++) {
            String mount = mMounts.get(i);
            if (!mVold.contains(mount))
                mMounts.remove(i--);
        }

        // don't need this anymore, clear the vold list to reduce memory
        // use and to prepare it for the next time it's needed.
        mVold.clear();
    }

    private static void testAndCleanMountsList() {
        /*
         * Now that we have a cleaned list of mount paths Test each one to make
         * sure it's a valid and available path. If it is not, remove it from
         * the list.
         */

        for (int i = 0; i < mMounts.size(); i++) {
            String mount = mMounts.get(i);
            File root = new File(mount);
            if (!root.exists() || !root.isDirectory() || !root.canWrite())
                mMounts.remove(i--);
        }
    }

    @SuppressWarnings("unchecked")
    private static void setProperties() {
        /*
         * At this point all the paths in the list should be valid. Build the
         * public properties.
         */
        Constants.mMounts = new ArrayList<String>();
        ArrayList<String> mLabels = new ArrayList<String>();

        int j = 0;
        if (mMounts.size() > 0) {
            if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD)
                mLabels.add("Auto");
            else if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
                if (Environment.isExternalStorageRemovable()) {
                    mLabels.add("External SD Card 1");
                    j = 1;
                } else
                    mLabels.add("Internal Storage");
            } else {
                if (!Environment.isExternalStorageRemovable()
                        || Environment.isExternalStorageEmulated())
                    mLabels.add("Internal Storage");
                else {
                    mLabels.add("External SD Card 1");
                    j = 1;
                }
            }

            if (mMounts.size() > 1) {
                for (int i = 1; i < mMounts.size(); i++) {
                    mLabels.add("External SD Card " + (i + j));
                }
            }
        }

        labels = new String[mLabels.size()];
        mLabels.toArray(labels);

        paths = new String[mMounts.size()];
        mMounts.toArray(paths);
        Constants.mMounts = (ArrayList<String>) mMounts.clone();
        Constants.mLabels = (ArrayList<String>) mLabels.clone();
        count = Math.min(labels.length, paths.length);

        // don't need this anymore, clear the mounts list to reduce memory
        // use and to prepare it for the next time it's needed.
        mMounts.clear();

    }
}

我从 SO 的一个类似问题中找到了这个，不幸的是我没有链接，但它可能在索尼的 Android 开发者网站上(不幸的是那里也没有链接)。 Wagic - 一个 C++ 游戏引擎库实现了相同的功能，它们的代码在这里:http://wagic.googlecode.com/svn-history/r4300/trunk/projects/mtg/Android/src/net/wagic/utils/StorageOptions.java所以你可以看看实现。我希望 Google 的人可以回答这个问题并提供一种从所有 Android 设备读取 SD 卡挂载点的单一方法