Get permanent path to a directory after user picks it with SAF with file picker

[decipher-cs]

My end goal is to allow the user to select favorite folders from their device storage (e.g. Music/playlist or Movies/horror) and then display the folder contents in the app. I am using capawesome's file picker to get permission to the folder but I want to persist the path of the user selected folder and also read its contents.

Is there any capacitor native way to do this or will I have to write my own plugin for it? I noticed that apps like VLC already support this so it's definitely something that android allows.

[erickdronski]

Android does not provide a permanent filesystem path for an SAF directory. The durable identifier is the returned content:// tree URI.

The intended pattern is:

1. Launch ACTION_OPEN_DOCUMENT_TREE.
2. Call takePersistableUriPermission on the returned URI.
3. Store uri.toString() in Preferences or a database.
4. Use ContentResolver and DocumentFile.fromTreeUri() to list and open its children.

For example, in the native Android result callback:

val uri = result.data?.data ?: return
val flags = result.data!!.flags and
    (Intent.FLAG_GRANT_READ_URI_PERMISSION or
     Intent.FLAG_GRANT_WRITE_URI_PERMISSION)

context.contentResolver.takePersistableUriPermission(uri, flags)

val files = DocumentFile
    .fromTreeUri(context, uri)
    ?.listFiles()
    .orEmpty()

Add the grant flags when creating the picker intent:

Intent(Intent.ACTION_OPEN_DOCUMENT_TREE).apply {
    addFlags(
        Intent.FLAG_GRANT_READ_URI_PERMISSION or
        Intent.FLAG_GRANT_WRITE_URI_PERMISSION or
        Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION or
        Intent.FLAG_GRANT_PREFIX_URI_PERMISSION
    )
}

One important Capawesome detail: its current Android pickDirectory implementation returns uri.toString() as path, but it does not call takePersistableUriPermission. Therefore saving result.path alone does not make the access durable across restarts.

Unless the plugin adds a persistence option, you will need a small native Capacitor plugin, a fork, or an upstream PR that persists the grant and exposes directory enumeration. Also check contentResolver.persistedUriPermissions when reopening the app because the user or provider can still revoke access.

So VLC is not holding a permanent POSIX path either; it is persisting the SAF tree URI and accessing it through Android's document APIs.

[robingenz]

The File Picker plugin now sets FLAG_GRANT_PERSISTABLE_URI_PERMISSION on the pickDirectory intent (see capawesome-team/capacitor-plugins#928), so the returned tree URI is now persistable. Note that takePersistableUriPermission() still needs to be called natively by whatever consumes the returned path — the plugin only makes the grant persistable, it doesn't take it for you.

[decipher-cs]

I have yet to try it but I'll mark this as the answer for now.

So I don't need to dabble in any native android code and it will just work?