How can I share a db file between 2 applications

Question

since Enviroment.getExternalStorageDirectory() is deprecated I have a little Problem. I have 2 applications (a lite and a pro version of an app). These apps have a database which I could export and import. When switching from lite to pro app, the user could import the "old" database into the new app. The database was stored under a folder inside his "sdcard". But now on Android 12 devices we no longer have access to that External Storage.

So how could I solve the problem?

Cause I think, context.getExternalFilesDir((Environment.DIRECTORY_DOCUMENTS) doesn't work cause the namespace of both apps are different. And I guess it will not work to open a file which is not located under the namespace of the app the file is requested.

Answer 1

Yes, sharing the app's shared memory with another one is not possible. Other options are using a external server / Firbase to create profile for users and store there data in it.

Answer 2

The easiest way is not to have two apps. Make the single app work for both modes, and gate features at runtime based on the type of license. You can even make the upgrade an in app purchase.

Answer 3

I found a solution by myself, but if someone else is looking for a solution it might be helpful.

I ask the user to specify a file location via

Intent intent = new Intent(Intent.ACTION_CREATE_DOCUMENT);
intent.addCategory(Intent.CATEGORY_OPENABLE);
intent.setType("application/db");
intent.putExtra(Intent.EXTRA_TITLE, "xyz.db");

mCreateNewDatabaseFile.launch(intent);

then in the mCreateNewDatabaseFile

private final ActivityResultLauncher<Intent> mCreateNewDatabaseFile = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {
    if (result.getResultCode() == RESULT_OK) {
        if (result.getData() != null && result.getData().getData() != null) {
            Uri path = result.getData().getData();
            getContentResolver().takePersistableUriPermission(path, Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
            getContentResolver().takePersistableUriPermission(path, Intent.FLAG_GRANT_READ_URI_PERMISSION);
            mPreferences.edit().putString(PREF_KEY_DATABASE_EXPORT_PATH, path.toString()).apply();
        }
    }
});

So even with another process I can read and write the file.

So in the lite Version I can create the db file and in the pro version I can let the user choose this file for import.

I hope it will help others with similar questions.

Answer 4

You can (should) use a ContentProvider to have other apps query your database using accessible methods of your ContentProvider:

you can configure a content provider to allow other applications to securely access and modify your app data

(this will enforce Single-responsibility principle )