I'm trying to build a kiosk app using android 5's screen pinning feature. It seems that all I need to do in the app was to call startLockTask(), but this still allows the user to leave the app by pressing the recent and back buttons.
To pin the app in a way that does not allow the user to leave it requires the app to be a device owner. Based on sites such as this one, one needs to run
adb shell dpm set-device-owner my.package.name/.MyAdminReceiver
in order to set the device owner. However, that command failed with
java.lang.IllegalStateException: Trying to set device owner but device is already provisioned.
which, I heard, is caused by the file /data/system/device_owner.xml already being present on the device.
Since the device had just been freshly factory-reset, I suspect that it had come with an app already provisioned by the manufacturer, so I rooted the device. I would rather do it without rooting (since there will be some 70 devices I have to run the procedure on) but for research purposes, it can't be helped.
After rooting the device, I tried to find the device_owner.xml file but it wasn't there. I tried creating one anyway based on this answer, but the app still shows the pinning message and the recent+back buttons still unpinned the app.
So why can't I set the device owner? is there any way around it?
While it's true that I tried dpm provisioning on a newly reset device, @basilisk's comment hinted me at the answer. The device comes loaded with bloatware that provides default accounts. Disabling these apps finally allowed me to provision the device with dpm.