How to check which StorageVolume we have access to, and which we don't?

Here is an alternate way to get what you want. It is a work-around like you have posted without using reflection or file paths.

On an emulator, I see the following items for which I have permitted access.

persistedUriPermissions array contents (value of URI only):

0 uri = content://com.android.externalstorage.documents/tree/primary%3A
1 uri = content://com.android.externalstorage.documents/tree/1D03-2E0E%3ADownload
2 uri = content://com.android.externalstorage.documents/tree/1D03-2E0E%3A
3 uri = content://com.android.externalstorage.documents/tree/primary%3ADCIM
4 uri = content://com.android.externalstorage.documents/tree/primary%3AAlarms

"%3A" is a colon (":"). So, it appears that the URI is constructed as follows for a volume where "<volume>" is the UUID of the volume.

uri = "content://com.android.externalstorage.documents/tree/<volume>:"

If the uri is a directory directly under a volume, then the structure is:

uri = "content://com.android.externalstorage.documents/tree/<volume>:<directory>"

For directories deeper in the structure, the format is:

uri = "content://com.android.externalstorage.documents/tree/<volume>:<directory>/<directory>/<directory>..."

So, it is just a matter of extracting volumes from URIs in these formats. The volume extracted can be used as a key for StorageManager.storageVolumes. The following code does just this.

It seems to me that there should be an easier way to go about this. There must be a missing linkage in the API between storage volumes and URIs. I can't say that this technique covers all circumstances.

I also question the UUID that is returned by storageVolume.uuid which seems to be a 32-bit value. I thought that UUIDs are 128 bits in length. Is this an alternative format for a UUID or somehow derived from the UUID? Interesting, and it is all about to drop! :(

MainActivity.kt

class MainActivity : AppCompatActivity() {    override fun onCreate(savedInstanceState: Bundle?) {        super.onCreate(savedInstanceState)        setContentView(R.layout.activity_main)        val storageManager = getSystemService(Context.STORAGE_SERVICE) as StorageManager        var storageVolumes = storageManager.storageVolumes        val storageVolumePathsWeHaveAccessTo = HashSet<String>()        checkAccessButton.setOnClickListener {            checkAccessToStorageVolumes()        }        requestAccessButton.setOnClickListener {            storageVolumes = storageManager.storageVolumes            val primaryVolume = storageManager.primaryStorageVolume            val intent = primaryVolume.createOpenDocumentTreeIntent()            startActivityForResult(intent, 1)        }    }    private fun checkAccessToStorageVolumes() {        val storageVolumePathsWeHaveAccessTo = HashSet<String>()        val persistedUriPermissions = contentResolver.persistedUriPermissions        persistedUriPermissions.forEach {            storageVolumePathsWeHaveAccessTo.add(it.uri.toString())        }        val storageManager = getSystemService(Context.STORAGE_SERVICE) as StorageManager        val storageVolumes = storageManager.storageVolumes        for (storageVolume in storageVolumes) {            val uuid = if (storageVolume.isPrimary) {                // Primary storage doesn't get a UUID here.                "primary"            } else {                storageVolume.uuid            }            val volumeUri = uuid?.let { buildVolumeUriFromUuid(it) }            when {                uuid == null ->                     Log.d("AppLog", "UUID is null for ${storageVolume.getDescription(this)}!")                storageVolumePathsWeHaveAccessTo.contains(volumeUri) ->                     Log.d("AppLog", "Have access to $uuid")                else -> Log.d("AppLog", "Don't have access to $uuid")            }        }    }    private fun buildVolumeUriFromUuid(uuid: String): String {        return DocumentsContract.buildTreeDocumentUri(            "com.android.externalstorage.documents",            "$uuid:"        ).toString()    }    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {        super.onActivityResult(requestCode, resultCode, data)        Log.d("AppLog", "resultCode:$resultCode")        val uri = data?.data ?: return        val takeFlags =            Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION        contentResolver.takePersistableUriPermission(uri, takeFlags)        Log.d("AppLog", "granted uri: ${uri.path}")    }}

EDIT: Found a workaround, but it might not work some day.

It uses reflection to get the real path of the StorageVolume instance, and it uses what I had before to get the path of persistedUriPermissions . If there are intersections between them, it means I have access to the storageVolume.

Seems to work on emulator, which finally has both internal storage and SD-card.

Hopefully we will get proper API and not need to use reflections.

If there is a better way to do it, without those kinds of tricks, please let me know.

So, here's an example:

MainActivity.kt

class MainActivity : AppCompatActivity() {    override fun onCreate(savedInstanceState: Bundle?) {        super.onCreate(savedInstanceState)        setContentView(R.layout.activity_main)        val storageManager = getSystemService(Context.STORAGE_SERVICE) as StorageManager        val storageVolumes = storageManager.storageVolumes        val primaryVolume = storageManager.primaryStorageVolume        checkAccessButton.setOnClickListener {            val persistedUriPermissions = contentResolver.persistedUriPermissions            val storageVolumePathsWeHaveAccessTo = HashSet<String>()            Log.d("AppLog", "got access to paths:")            for (persistedUriPermission in persistedUriPermissions) {                val path = FileUtilEx.getFullPathFromTreeUri(this, persistedUriPermission.uri)                        ?: continue                Log.d("AppLog", "path: $path")                storageVolumePathsWeHaveAccessTo.add(path)            }            Log.d("AppLog", "storage volumes:")            for (storageVolume in storageVolumes) {                val volumePath = FileUtilEx.getVolumePath(storageVolume)                if (volumePath == null) {                    Log.d("AppLog", "storageVolume \"${storageVolume.getDescription(this)}\" - failed to get volumePath")                } else {                    val hasAccess = storageVolumePathsWeHaveAccessTo.contains(volumePath)                    Log.d("AppLog", "storageVolume \"${storageVolume.getDescription(this)}\" - volumePath:$volumePath - gotAccess? $hasAccess")                }            }        }        requestAccessButton.setOnClickListener {            val intent = primaryVolume.createOpenDocumentTreeIntent()            startActivityForResult(intent, 1)        }    }    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {        super.onActivityResult(requestCode, resultCode, data)        Log.d("AppLog", "resultCode:$resultCode")        val uri = data?.data ?: return        val takeFlags = Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION        contentResolver.takePersistableUriPermission(uri, takeFlags)        val fullPathFromTreeUri = FileUtilEx.getFullPathFromTreeUri(this, uri)        Log.d("AppLog", "granted uri:$uri $fullPathFromTreeUri")    }}

FileUtilEx.java

/** * Get the full path of a document from its tree URI. * * @param treeUri The tree RI. * @return The path (without trailing file separator). */public static String getFullPathFromTreeUri(Context context, final Uri treeUri) {    if (treeUri == null)        return null;    String volumePath = getVolumePath(context, getVolumeIdFromTreeUri(treeUri));    if (volumePath == null)        return File.separator;    if (volumePath.endsWith(File.separator))        volumePath = volumePath.substring(0, volumePath.length() - 1);    String documentPath = getDocumentPathFromTreeUri(treeUri);    if (documentPath.endsWith(File.separator))        documentPath = documentPath.substring(0, documentPath.length() - 1);    if (documentPath.length() > 0)        if (documentPath.startsWith(File.separator))            return volumePath + documentPath;        else return volumePath + File.separator + documentPath;    return volumePath;}public static String getVolumePath(StorageVolume storageVolume){    if (VERSION.SDK_INT < VERSION_CODES.LOLLIPOP)        return null;    try{        final Class<?> storageVolumeClazz = StorageVolume.class;        final Method getPath = storageVolumeClazz.getMethod("getPath");        return (String) getPath.invoke(storageVolume);    } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {        e.printStackTrace();    }    return null;}/** * Get the path of a certain volume. * * @param volumeId The volume id. * @return The path. */@SuppressLint("ObsoleteSdkInt")private static String getVolumePath(Context context, final String volumeId) {    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP)        return null;    try {        final StorageManager storageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {            final Class<?> storageVolumeClazz = StorageVolume.class;            //noinspection JavaReflectionMemberAccess            final Method getPath = storageVolumeClazz.getMethod("getPath");            final List<StorageVolume> storageVolumes = storageManager.getStorageVolumes();            for (final StorageVolume storageVolume : storageVolumes) {                final String uuid = storageVolume.getUuid();                final boolean primary = storageVolume.isPrimary();                // primary volume?                if (primary && PRIMARY_VOLUME_NAME.equals(volumeId)) {                    return (String) getPath.invoke(storageVolume);                }                // other volumes?                if (uuid != null && uuid.equals(volumeId))                    return (String) getPath.invoke(storageVolume);            }            return null;        }        final Class<?> storageVolumeClazz = Class.forName("android.os.storage.StorageVolume");        final Method getVolumeList = storageManager.getClass().getMethod("getVolumeList");        final Method getUuid = storageVolumeClazz.getMethod("getUuid");        //noinspection JavaReflectionMemberAccess        final Method getPath = storageVolumeClazz.getMethod("getPath");        final Method isPrimary = storageVolumeClazz.getMethod("isPrimary");        final Object result = getVolumeList.invoke(storageManager);        final int length = Array.getLength(result);        for (int i = 0; i < length; i++) {            final Object storageVolumeElement = Array.get(result, i);            final String uuid = (String) getUuid.invoke(storageVolumeElement);            final Boolean primary = (Boolean) isPrimary.invoke(storageVolumeElement);            // primary volume?            if (primary && PRIMARY_VOLUME_NAME.equals(volumeId)) {                return (String) getPath.invoke(storageVolumeElement);            }            // other volumes?            if (uuid != null && uuid.equals(volumeId))                return (String) getPath.invoke(storageVolumeElement);        }        // not found.        return null;    } catch (Exception ex) {        return null;    }}/** * Get the document path (relative to volume name) for a tree URI (LOLLIPOP). * * @param treeUri The tree URI. * @return the document path. */@TargetApi(VERSION_CODES.LOLLIPOP)private static String getDocumentPathFromTreeUri(final Uri treeUri) {    final String docId = DocumentsContract.getTreeDocumentId(treeUri);    //TODO avoid using spliting of a string (because it uses extra strings creation)    final String[] split = docId.split(":");    if ((split.length >= 2) && (split[1] != null))        return split[1];    else        return File.separator;}/** * Get the volume ID from the tree URI. * * @param treeUri The tree URI. * @return The volume ID. */@TargetApi(VERSION_CODES.LOLLIPOP)private static String getVolumeIdFromTreeUri(final Uri treeUri) {    final String docId = DocumentsContract.getTreeDocumentId(treeUri);    final int end = docId.indexOf(':');    String result = end == -1 ? null : docId.substring(0, end);    return result;}

activity_main.xml

<LinearLayout  xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"  android:gravity="center" android:orientation="vertical" tools:context=".MainActivity">  <Button    android:id="@+id/checkAccessButton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="checkAccess"/>  <Button    android:id="@+id/requestAccessButton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="requestAccess"/></LinearLayout>

To put it in a simple function, here:

/** for each storageVolume, tells if we have access or not, via a HashMap (true for each iff we identified it has access*/fun getStorageVolumesAccessState(context: Context): HashMap<StorageVolume, Boolean> {    val storageManager = context.getSystemService(Context.STORAGE_SERVICE) as StorageManager    val storageVolumes = storageManager.storageVolumes    val persistedUriPermissions = context.contentResolver.persistedUriPermissions    val storageVolumePathsWeHaveAccessTo = HashSet<String>()    //            Log.d("AppLog", "got access to paths:")    for (persistedUriPermission in persistedUriPermissions) {        val path = FileUtilEx.getFullPathFromTreeUri(context, persistedUriPermission.uri)                ?: continue        //                Log.d("AppLog", "path: $path")        storageVolumePathsWeHaveAccessTo.add(path)    }    //            Log.d("AppLog", "storage volumes:")    val result = HashMap<StorageVolume, Boolean>(storageVolumes.size)    for (storageVolume in storageVolumes) {        val volumePath = FileUtilEx.getVolumePath(storageVolume)        val hasAccess = volumePath != null && storageVolumePathsWeHaveAccessTo.contains(volumePath)        result[storageVolume] = hasAccess    }    return result}

for API 30 (Android 11)

@TargetApi(30)private fun getVolumePathApi30(context:Context, uuid: String): String{    // /storage/emulated/0/Android/data/{packageName}/files    // /storage/0222-9FE1/Android/data/{packageName}/files    val list = ContextCompat.getExternalFilesDirs(context, null).map{ it.canonicalPath.replace(reAndroidDataFolder, "") }    // /storage/emulated/0    // /storage/0222-9FE1    val path = if( uuid == "primary") {        list.firstOrNull()    }else {        list.find { it.contains(uuid, ignoreCase = true) }    }    return path ?: error("can't find volume for uuid $uuid")}