Hey there, NVIDIA Shield user here too. I've managed to do this without root. You should use something similar to this in the launcher config:
<application>/system/bin/am</application>
<args>start --user 0 -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -e ROM "%rom%" -e LIBRETRO /data/data/com.retroarch/cores/picodrive_libretro_android.so -e CONFIGFILE sdcard/Android/data/com.retroarch/files/retroarch.cfg -e IME com.android.inputmethod.latin/.LatinIME -n com.retroarch/.browser.retroactivity.RetroActivityFuture</args>
What you're doing with the command and arguments is simulating what a home launcher would do:
/system/bin/am is the activity manager from Android which is pretty much the thing that actually does the starting of the program.
The arguments itself is a mix of a few things: It gives over the start command and starts the activity through the LAUNCHER intent. The LAUNCHER intent is what makes the app know what to do when you're starting from your home screen on your phone/tablet/Mi.
There are two reasons for why we're doing this:
1. The installed APK of an app actually gets extracted on installation and the executable dex is moved to dalvik-cache (see [url="https://android.stackexchange.com/questions/5147/the-installation-steps-of-android-package"]this tiny explanation[/url]) which is the thing that Android knows what com.retroarch is.
2. Apps has to be used as generally Android apps can have different activites for when it's booted for specific situations (standard is DEFAULT and LAUNCHER) so we have to specify this.
This is pretty much the reason why with the combination of /system/bin/am and the arguments you're able to boot up apps without root.
You can mix and match this up with anything (best way would be to google). For example for Yabause I'm ujsing this:
<application>/system/bin/am</application>
<args>start --user 0 -n org.uoyabause.uranus/org.uoyabause.android.Yabause -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -e org.uoyabause.android.FileNameEx "$rom$"</args>
Now for the permission question:
The app has to ask for permissions at start first. That's indicated by the pop up asking "Allow xxxx to access photos, media, and fies on your device?". If you say yes then:
- The app has full read permissions on the
whole drive.
- The app has limited write permissions on the external drive. This is for example /data/com.retroarch
I've been able to get AEL to access a ROM folder on my drive and let RetroArch load the ROMs just fine. It's always important that if there's anything that needs to be rewritable, like a config file, you have to use the designated /data/ folder.
