无法访问 Android 上的外部 sd 卡

Question

I have easily accessed Internal Storage Files using

File internalStorage = new File( Environment.getExternalStorageDirectory().getAbsolutePath() );     
internalStorage.listFiles();

And i am getting all the files. But i am unable to get any file from my mounted sd-card. i have checked. if SD-Card is mounted

boolean isSdCard = android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED);

And i have also tried different solutions like.

File sdCardFolder = new File(System.getenv("SECONDARY_STORAGE"));   
//RESULT.    
sdCardFolder.getName() //sdcard0.   
sdCardFolder.listFile() //null.

Here it's giving the folder name but sending null for listFile.

And also i have tried different other methods to listFiles from my SD Card but unable to find a working one.

in build.gradle.

compileSdkVersion 31.    
targetSdkVersion 31

Answer 1

Check and ask for permission to access external cards in your manifest or by code

Answer 2

After a lot of research and time consumed. I finally got a solution for my Question. There are plenty of questions asked for the same problem but not any relevant and working is availible, up-till my exposure.

I am answering my own question to help others facing same problem. I have used the following code to get the path of SD-Card. And then i have accessed it normally as i have accessed internel storage of Android Device.

//THE FOLLOWING FUNCTION WILL RETURN THE PATH OF SD-Card, AND NULL IF NO SD CARD MOUNTED


public static String getExternalStoragePath(Context mContext, boolean is_removable) {

        StorageManager mStorageManager = (StorageManager) mContext.getSystemService(Context.STORAGE_SERVICE);
        Class<?> storageVolumeClazz = null;
        try {
            storageVolumeClazz = Class.forName("android.os.storage.StorageVolume");
            Method getVolumeList = mStorageManager.getClass().getMethod("getVolumeList");
            Method getPath = storageVolumeClazz.getMethod("getPath");
            Method isRemovable = storageVolumeClazz.getMethod("isRemovable");
            Object result = getVolumeList.invoke(mStorageManager);
            final int length = Array.getLength(result);
            for (int i = 0; i < length; i++) {
                Object storageVolumeElement = Array.get(result, i);
                String path = (String) getPath.invoke(storageVolumeElement);
                boolean removable = (Boolean) isRemovable.invoke(storageVolumeElement);
                if (is_removable == removable) {
                    return path;
                }
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return null;
    }

Answer 3

To add on to @Saqib's answer, I've simplified the code by removing the need to use his helper/wrapper class.

 StorageManager storageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);
 List<StorageVolume> storageArray = storageManager.getStorageVolumes();
 String path = "";
 for (StorageVolume item : storageArray)
     if (item.isRemovable())
           if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R)
                path = item.getDirectory().getPath();

To handle null case, simply check if the path string is empty or null and handle that appropriately.