[Interest] Is there a full FileDialog example for Android with writing and saving files?

[Marius Kittler]

> W DRC     : java.lang.SecurityException: Permission Denial: reading
> com.android.externalstorage.ExternalStorageProvider uri
> content://com.android.externalstorage.documents/document/primary%3ADownload
> %2Fbankdrc.dbf from pid=15086, uid=10502 requires that you obtain access
> using ACTION_OPEN_DOCUMENT or related APIs
> 
> There is a lot of boiler plate to handle the permissions to write to the
> system.
> 
> Is there any example where this boiler plate code can be found?
> 

Hi, I don't know any official example. The last Android-related point on the 
QFile documentation suggests that Qt might not be of much help when it comes 
to consuming content URLs (see https://doc.qt.io/qt-6/qfile.html).

I once wrote an app that is able to read and write content URLs using standard 
I/O streams. You can find it here: https://github.com/Martchus/passwordmanager
It was written before Qt had support for Android file dialogs so I did that 
part manually (but now you should of course rely on Qt for that). You could 
probably also just use the QFile overload that takes a file descriptor instead 
of using standard I/O streams because the latter is actually very involved. (I 
only did it because my code was already using I/O streams.)

Another approach is to ditch the weird content URLs and work with normal 
paths. For this you need to "convert" the content URL to a normal path. You 
can find (probably very hacky) code on another project I'm currently working 
on:
https://github.com/Martchus/syncthingtray/blob/master/tray/android/src/io/
github/martchus/syncthingtray/Util.java
Here I chose this approach because I also wanted to use std::filesystem and Go 
code so this content stuff just gets in the way. I have actually just tested 
whether this works on a real device and it does on an Android 14 one - even 
writing to the SD card. You will most likely run into permission errors under 
older Android versions. Not sure as of what version this approach works. I 
think this approach also relies much on super greedy permissions (see https://
github.com/Martchus/syncthingtray/blob/
49e898644b8c1f4bdbcef2a2ddb8f4fcd410bdef/tray/resources/
AndroidManifest.xml.in#L11C55-L11C78) so that would be problematic if you 
wanted to publish the app on Google Play.

Best Regards
Marius