[Interest] Problems writing files to Android file system on some newer devices using QStandardPaths

[Jérôme Godbout]

You might check the best path for the Android application depending on your needs:
https://developer.android.com/guide/topics/data

Then compare with the QStandards path, I’m not sure they are all friendly with the scoped storage.

For the actual path resolving are written down into the documentation (scroll down a little after the enum):
https://doc.qt.io/qt-5/qstandardpaths.html#StandardLocation-enum

Anything that use <APPROOT> for mobile is protected against other now and are part of the scoped storage. Note, you cannot write into the actual application binary anymore and other application based binary.

AppLocalDataLocation, ConfigLocation
should be safe for example. DataLocation should also be ok too normally. But make sure the path resolved make sense and play well with scoped storage. Try to keep the data as private as much as possible depending on your requirement. It’s easier to expose data later then loosing access to it! You can expose the data into a more public when needed with an application update, loosing access to a path with an update will prevent you from migrating those data.

Make sure you ask for the proper permission (manifest.xml) and at runtime to access the storage with your application (note the read/write external storage on Android 11 doesn’t do much since there is now the scoped storage that is more restrictive, but you will still need them for older Android version). Normally that should work for both internal and external storage data, the internal data storage is now encrypted and therefore should be used for sensitive data.

Jérôme Godbout, B. Ing.

Software / Firmware Team Lead
O: (418) 682-3636 ext.: 114
C: (581) 777-0050
godboutj at dimonoff.com<mailto:godboutj at dimonoff.com>
[signature_1620770654]<https://www.dimonoff.com/>
dimonoff.com<https://www.dimonoff.com/>
1015 Avenue Wilfrid-Pelletier,
Québec, QC G1W 0C4, 4e étage


From: Nuno Santos <nuno.santos at imaginando.pt>
Date: Tuesday, May 25, 2021 at 12:02 PM
To: Jérôme Godbout <godboutj at amotus.ca>
Cc: Qt Interest <interest at qt-project.org>
Subject: Re: [Interest] Problems writing files to Android file system on some newer devices using QStandardPaths
Jerome,

Thank you very much for your reply and for the link.

DocumentsLocation is point to /storage/emulated/…

But I’ve been trying with other QStandardPath such as ConfigLocation and DataLocation. Those were point to something like /user/app_identififier_/files/, can’t remember exactly now. But when trying to write to those locations, it would always fail.

Are QStandardPath Android locations compatible with Scoped Storage? Would I need to refactor my Qt code or this is just a thing we need to enable in the app manifest?

Thank you!

Best regards,

Nuno

On 25 May 2021, at 14:22, Jérôme Godbout <godboutj at amotus.ca<mailto:godboutj at amotus.ca>> wrote:

Where the standard path resolve on the device?

On Android 10, they changed the way we can access the file system, you can opt out with android:requestLegacyExternalStorage=“true” but this flag doesn’t work for Android 11+. If removing this flag break your applications, it means your application won’t work on any Android 11 devices.

The application are now sandboxed, Android 10 make it optional, Android 11 enforce it. You need to move to scoped storage.
https://developer.android.com/about/versions/11/privacy/storage


Jérôme Godbout, B. Ing.

Software / Firmware Team Lead
O: (418) 682-3636 ext.: 114
C: (581) 777-0050
godboutj at dimonoff.com<mailto:godboutj at dimonoff.com>
<image001.png><https://www.dimonoff.com/>
dimonoff.com<https://www.dimonoff.com/>
1015 Avenue Wilfrid-Pelletier,
Québec, QC G1W 0C4, 4e étage


From: Interest <interest-bounces at qt-project.org<mailto:interest-bounces at qt-project.org>> on behalf of Nuno Santos <nuno.santos at imaginando.pt<mailto:nuno.santos at imaginando.pt>>
Date: Monday, May 24, 2021 at 8:17 AM
To: Qt Interest <interest at qt-project.org<mailto:interest at qt-project.org>>
Subject: [Interest] Problems writing files to Android file system on some newer devices using QStandardPaths
Hi,

Is anyone aware of changes to the way that Android filesystem works and how Qt interacts with it?

I’ve been writing to QStandardPaths::DocumentLocations without any issues until. However, on some newer devices, it fails to open files for writing. One example is Samsung Tab A (SM-T500)

It seems though that using android:requestLegacyExternalStorage=“true” seems to fix the problem but this solution will not last long because it seems it will be ignored when the app targets API 30 (Android 11):

https://developer.android.com/training/data-storage/use-cases

Caution: After you update your app to target Android 11 (API level 30), the system ignores the requestLegacyExternalStorage attribute<https://developer.android.com/about/versions/11/privacy/storage#scoped-storage> when your app is running on Android 11 devices, so your app must be ready to support scoped storage and to migrate app data<https://developer.android.com/training/data-storage/use-cases#migrate-legacy-storage> for users on those devices.

Is there any common knowledge about this?

Thanks!

Regards,

Nuno

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.qt-project.org/pipermail/interest/attachments/20210525/b932f94a/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 13928 bytes
Desc: image001.png
URL: <http://lists.qt-project.org/pipermail/interest/attachments/20210525/b932f94a/attachment-0001.png>