Android中如何判断SD卡是否挂载？

Question

我正在开发一个 Android 应用程序，需要查看用户存储了哪些图像。 问题是，如果用户通过 USB 电缆安装了 SD 卡，我无法读取磁盘上的图像列表。

有谁知道有什么方法可以判断 USB 是否已安装，以便我可以弹出一条消息，通知用户它无法工作？

Answer 1

如果您尝试访问设备上的图像，最好的方法是使用 MediaStore 内容提供商。 作为内容提供商访问它将允许您查询图像并在适当的情况下将 content:// URL 映射到设备上的文件路径。

如果您仍然需要访问 SD 卡，相机应用程序包含 ImageUtils 类，用于检查 SD 卡是否安装如下：

static public boolean hasStorage(boolean requireWriteAccess) {
    //TODO: After fix the bug,  add "if (VERBOSE)" before logging errors.
    String state = Environment.getExternalStorageState();
    Log.v(TAG, "storage state is " + state);

    if (Environment.MEDIA_MOUNTED.equals(state)) {
        if (requireWriteAccess) {
            boolean writable = checkFsWritable();
            Log.v(TAG, "storage writable is " + writable);
            return writable;
        } else {
            return true;
        }
    } else if (!requireWriteAccess && Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        return true;
    }
    return false;
}

Answer 2

这是 jargonjustin 帖子中缺少的 checkFsWritable 函数

private static boolean checkFsWritable() {
        // Create a temporary file to see whether a volume is really writeable.
        // It's important not to put it in the root directory which may have a
        // limit on the number of files.
        String directoryName = Environment.getExternalStorageDirectory().toString() + "/DCIM";
        File directory = new File(directoryName);
        if (!directory.isDirectory()) {
            if (!directory.mkdirs()) {
                return false;
            }
        }
        return directory.canWrite();
    }

Answer 3

public static boolean isSdPresent() {

return android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED);

}

Answer 4

我很抱歉发布了一种非 Android 方式来执行此操作，希望有人可以使用 Android API 提供答案。

您可以列出 SD 卡根目录下的文件。 如果没有，则 SD 卡要么完全空白（不常见，但可能），要么已卸载。 如果您尝试在 sdcard 上创建一个空文件并且失败，则意味着您尝试在 sdcard 的挂载点中创建一个文件，该文件会因权限问题而被拒绝，因此您会知道 sdcard 不是安装。

是的，我知道这很丑......

Answer 5

在行话贾斯汀的帖子上：

文件 ImageManager.java

方法hasStorage -->

public static boolean hasStorage(boolean requireWriteAccess) {
        String state = Environment.getExternalStorageState();

        if (Environment.MEDIA_MOUNTED.equals(state)) {
            if (requireWriteAccess) {
                boolean writable = checkFsWritable();
                return writable;
            } else {
                return true;
            }
        } else if (!requireWriteAccess
                && Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
            return true;
        }
        return false;
    }

方法checkFsWritable -->

 private static boolean checkFsWritable() {
        // Create a temporary file to see whether a volume is really writeable.
        // It's important not to put it in the root directory which may have a
        // limit on the number of files.
        String directoryName =
                Environment.getExternalStorageDirectory().toString() + "/DCIM";
        File directory = new File(directoryName);
        if (!directory.isDirectory()) {
            if (!directory.mkdirs()) {
                return false;
            }
        }
        File f = new File(directoryName, ".probe");
        try {
            // Remove stale file if any
            if (f.exists()) {
                f.delete();
            }
            if (!f.createNewFile()) {
                return false;
            }
            f.delete();
            return true;
        } catch (IOException ex) {
            return false;
        }
    }

Answer 6

我使用光标从 SD 卡检索图像，当设备中没有插入 SD 卡时，光标为空。
实际上，这是通过从设备中物理移除卡来卸载 SD 卡卷时的情况。 这是我使用过的代码：

  Cursor mCursor = this.getContentResolver().query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, null, null, null, null);
    if (mCursor == null || !mCursor .moveToFirst()) {
                /**
                 *mCursor == null:
                 * - query failed; the app don't have access to sdCard; example: no sdCard 
                 *
                 *!mCursor.moveToFirst():
                 *     - there is no media on the device
                 */
            } else {
                 // process the images...
                 mCursor.close(); 
    }

更多信息：http://developer .android.com/guide/topics/media/mediaplayer.html#viacontentresolver

Answer 7

在对外部存储进行任何操作之前，您应该始终调用 getExternalStorageState() 来检查媒体是否可用。 该介质可能已安装到计算机、丢失、只读或处于某种其他状态。 例如，您可以使用以下几种方法来检查可用性：

/* Checks if external storage is available for read and write */
public boolean isExternalStorageWritable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        return true;
    }
    return false;
}

/* Checks if external storage is available to at least read */
public boolean isExternalStorageReadable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state) ||
        Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        return true;
    }
    return false;
}

来源：
http://developer.android.com/guide/topics/data/data -存储.html

Answer 8

Cool....Check it out...
try {
            File mountFile = new File("/proc/mounts");
            usbFoundCount=0;
            sdcardFoundCount=0;
            if(mountFile.exists())
             {
                Scanner usbscanner = new Scanner(mountFile);
                while (usbscanner.hasNext()) {
                    String line = usbscanner.nextLine();
                    if (line.startsWith("/dev/fuse /storage/usbcard1")) {
                        usbFoundCount=1;
                        Log.i("-----USB--------","USB Connected and properly mounted---/dev/fuse /storage/usbcard1" );
                    }
            }
         }
            if(mountFile.exists()){
                Scanner sdcardscanner = new Scanner(mountFile);
                while (sdcardscanner.hasNext()) {
                    String line = sdcardscanner.nextLine();
                    if (line.startsWith("/dev/fuse /storage/sdcard1")) {
                        sdcardFoundCount=1;
                        Log.i("-----USB--------","USB Connected and properly mounted---/dev/fuse /storage/sdcard1" );
                    }
            }
         }
            if(usbFoundCount==1)
            {
                Toast.makeText(context,"USB Connected and properly mounted", 7000).show();
                Log.i("-----USB--------","USB Connected and properly mounted" );
            }
            else
            {
                Toast.makeText(context,"USB not found!!!!", 7000).show();
                Log.i("-----USB--------","USB not found!!!!" );

            }
            if(sdcardFoundCount==1)
            {
                Toast.makeText(context,"SDCard Connected and properly mounted", 7000).show();
                Log.i("-----SDCard--------","SDCard Connected and properly mounted" );
            }
            else
            {
                Toast.makeText(context,"SDCard not found!!!!", 7000).show();
                Log.i("-----SDCard--------","SDCard not found!!!!" );

            }
        }catch (Exception e) {
            e.printStackTrace();
        }