This app tries to access GPIO through NDK to achieve higher speeds than are possible using Java API.
Before running app start listening server with
./app/src/main/scripts/runListener.sh
Keep it opened. You only need to run it once each time you boot your Android Thing. Tested on Raspberry Pi 3 only. If it stops running start it again at anytime.
To check that it's actually check that gpio_export_pipe exists:
adb -s Android.local shell "ls -l /data/data/com.amazingapps.sample.thingssample/gpio_export_pipe"
While your program is running you'll see some text on the terminal every time a new pin is opened. Verify that it's working as expected by:
adb -s Android.local shell "ls -l /sys/class/gpio/gpio23"
and check that gpio23 folder exists, and both direction and value have read and write permissions for all users (you should see -rw-rw-rw next to it).