How to gain access to a specific folder and write a file into it using Scoped Storage

Question

My app has a feature that exports GPS data in txt format into a shared folder (now accessed with getExternalStorageDirectory), and I have to switch it to Scoped Storage (API 30).
(As information, the app is the open source GPS Logger for Android.)

In the future I would let the users choose the folder to be used for the exportation, using:

public void openDirectory(Uri uriToLoad) {
    // Choose a directory using the system's file picker.
    Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
    startActivityForResult(intent, your-request-code);
}

public void onActivityResult(int requestCode, int resultCode,
        Intent resultData) {
    if (requestCode == your-request-code && resultCode == Activity.RESULT_OK) {
        // The result data contains a URI for the directory that the user selected.
        Uri uri = null;
        if (resultData != null) {
            uri = resultData.getData();
            // Perform operations on the document using its URI.
        }
    }
}

This way my app will gain access to the selected folder.

How can I create a text file into that folder and write data using a BufferedWriter?

I know that maybe I can use something like:

...
Uri fileUri = // Something related to the previous uri, but I cannot find the solution
OutputStream outputStream = getContentResolver().openOutputStream(fileUri, "rw");
txtBW = new BufferedWriter(new OutputStreamWriter(outputStream));
...

but I found nothing that works.

Answer 1

DocumentFile is Google's somewhat clunky solution for navigating through document trees. The recipe for what you want should be:

• Take the Uri that you got for your tree and wrap it in a DocumentFile using DocumentFile.fromTreeUri()
• Call createFile() on that DocumentFile, supplying a filename or other display name, which will give you a DocumentFile representing that document
• Call getUri() on the document's DocumentFile to get a Uri representing the document
• Use openOutputStream() on a ContentResolver to write your desired content to that Uri

Note that if you need long-term access to this tree, be sure to call takePersistableUriPermission() on a ContentResolver, passing in the Uri for the document tree. That should give you access to the tree and all documents inside of it.

Answer 2

1-You can create a target path like this (I'm targetting the "Android/media" folder)

 private const val ROOT_FOLDER = "primary:"
 private const val ANDROID_MEDIA = "${ROOT_FOLDER}Android/media"
 private const val EXTERNAL_STORAGE_PROVIDER_AUTHORITY = "com.android.externalstorage.documents"

2- Create URI and intent object

val storageManager = getSystemService(Context.STORAGE_SERVICE) as StorageManager
val uri =DocumentsContract.buildDocumentUri(EXTERNAL_STORAGE_PROVIDER_AUTHORITY,
                ANDROID_MEDIA)
val intent = storageManager.primaryStorageVolume.createOpenDocumentTreeIntent()
                .putExtra(DocumentsContract.EXTRA_INITIAL_URI,uri)

3- Register activity for results

for example

private val openDocumentTreeLauncher =
    registerForActivityResult(ActivityResultContracts.StartActivityForResult()) {
        if (it.resultCode == RESULT_OK) {
            val data: Uri = it.data?.data!!
            contentResolver.takePersistableUriPermission(
                data,
                Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION
            )}

finally launch the Activity for results

openDocumentTreeLauncher.launch(intent)