Storage Access Framework

[ahmedre]

In preparation for the Storage Access Framework, Quran for Android should reconsider how it deals with files. This is required since we'll lose the ability to write to external storage (outside of our own data directory) in the next version (and, potentially, even on Android Q if we don't set the legacy storage flag).

Proposal:

• make the default for storing images one of the /Android/data directories.
• for people pre-api 29, allow specifying a custom path for data storage (as per #705).

This will require a migration - people currently using /sdcard/quran_android need to be explicitly migrated to internal storage somehow - especially people on newer api versions that are either on Q now and/or are likely to get upgraded to the next version of Android.

on launch, the app today requests sd card permissions - some initial thoughts are that perhaps the phases can be as follows:

• phase 1 - sdcard permission is still asked, and, if granted, we check if the images are there - if they are, copy them into /Android/data, otherwise, set the data directory to /Android/data. this only happens for fresh installs. if we can detect if this is a new install (i.e. nothing in shared prefs that are backed up to Google), perhaps don't even prompt.
• phase 2 - existing installs on newer versions that write to the sdcard (without having explicitly changed the directory) do a one time copy into /Android/data and stop using the sdcard.
• phase 3 - stop asking for external write permissions for fresh installs and provide a way to check and copy the files from the old path.

[ahmedre]

i actually did all 3 steps mentioned above in one go -

as of #1452, the default write directory for all new installations (or cleared data installations) is context.getExternalFilesDir, which is the application specific directory that no longer needs special permissions to read or write.

moreover, on Android 29 and above, a migration happens whenever someone is using /sdcard - the data is copied to context.getExternalFilesDir and the old directory is removed. note that we opt out of scoped storage in Android 29 to make this possible.

(note that this is safe irrespective of someone having set a custom location - the reason is that as of api 19 and above, the only custom locations settable are those returned by getExternalFilesDirs, which are all writeable without permissions on new apis and are safe to write to).

in sha' Allah after some time, we can target Android 30 with almost no additional changes (except for adding preserveLegacyExternalStorage to the manifest and removing /sdcard as an option from the advanced settings dialog).

note that, for now, i am keeping the /sdcard option in advanced settings - this is to allow someone who copied the data from another device and then installed the app to be able to go to advanced settings, switch to the sdcard, and regain their data without re-downloading everything. in the future, however, this should be removed for api 30 and above in sha' Allah.