Question

我过去常常从"/storage/external_storage"获取 USB / SD卡中的所有文件

File = new File("/storage/external_storage");
file.listFiles()

并在我自己的Fragment中显示文件和文件夹，它在API 23之前运行良好。现在我无法从路径中获取文件列表。

我知道在Android Marshmallow（23）中有权限更改和某些USB Connection行为更改。

如果您的应用支持用户通过USB端口与设备进行互动，请考虑必须明确启用互动。

不解释用户何时或何时可以明确启用交互。

我的问题是是否可以访问USB文件和文件夹列表。如果有，我们怎样才能做到这一点？

编辑：我打开了Android设备监视器，我在external_storage找不到/storage/external_storage。

Answer 1

文档对此并不十分清楚......但似乎您必须要求系统为您安装媒体设备。你可以尝试使用吗？ Environment.getExternalStorageState()看看它给你的回报是什么？

否则，您也可以尝试使用此类访问SD /外部USB：

public class ExternalStorage {

public static final String SD_CARD = "sdCard";
public static final String EXTERNAL_SD_CARD = "externalSdCard";

/**
 * @return True if the external storage is available. False otherwise.
 */
public static boolean isAvailable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state) || Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        return true;
    }
    return false;
}

public static String getSdCardPath() {
    return Environment.getExternalStorageDirectory().getPath() + "/";
}

/**
 * @return True if the external storage is writable. False otherwise.
 */
public static boolean isWritable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        return true;
    }
    return false;

}

/**
 * @return A map of all storage locations available
 */
public static Map<String, File> getAllStorageLocations() {
    Map<String, File> map = new HashMap<String, File>(10);

    List<String> mMounts = new ArrayList<String>(10);
    List<String> mVold = new ArrayList<String>(10);
    mMounts.add("/mnt/sdcard");
    mVold.add("/mnt/sdcard");

    try {
        File mountFile = new File("/proc/mounts");
        if(mountFile.exists()){
            Scanner scanner = new Scanner(mountFile);
            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) {
        e.printStackTrace();
    }

    try {
        File voldFile = new File("/system/etc/vold.fstab");
        if(voldFile.exists()){
            Scanner scanner = new Scanner(voldFile);
            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(":"));
                    if (!element.equals("/mnt/sdcard"))
                        mVold.add(element);
                }
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }


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

    List<String> mountHash = new ArrayList<String>(10);

    for(String mount : mMounts){
        File root = new File(mount);
        if (root.exists() && root.isDirectory() && root.canWrite()) {
            File[] list = root.listFiles();
            String hash = "[";
            if(list!=null){
                for(File f : list){
                    hash += f.getName().hashCode()+":"+f.length()+", ";
                }
            }
            hash += "]";
            if(!mountHash.contains(hash)){
                String key = SD_CARD + "_" + map.size();
                if (map.size() == 0) {
                    key = SD_CARD;
                } else if (map.size() == 1) {
                    key = EXTERNAL_SD_CARD;
                }
                mountHash.add(hash);
                map.put(key, root);
            }
        }
    }

    mMounts.clear();

    if(map.isEmpty()){
             map.put(SD_CARD, Environment.getExternalStorageDirectory());
    }
    return map;
}
}

用法是这样的：

Map<String, File> externalLocations = ExternalStorage.getAllStorageLocations();
File sdCard = externalLocations.get(ExternalStorage.SD_CARD);
File externalSdCard = externalLocations.get(ExternalStorage.EXTERNAL_SD_CARD);

来源：Find an external SD card location

Answer 2

看看getExternalFilesDirs()。如果插入micro SD卡，则第二个条目将指向卡。如果您随后连接USB OTG驱动器，则第三个条目将指向驱动器。

使用Intent.ACTION_OPEN_DOCUMENT_TREE，您可以让用户从所有驱动器中进行选择，然后使用存储访问框架。

Android - API 23无法获取USB / SD卡目录

2 个答案: