Android O Developer Preview emulator always OFFLINE

Question

I'm trying to test my app against the Android O developer preview. I can download and run the emulator, but when deploying my app, it always comes up as "[OFFLINE]". If I go ahead and try to deploy anyway, I get the following output:

com.android.ddmlib.AdbCommandRejectedException: device unauthorized.
This adb server's $ADB_VENDOR_KEYS is not set
Try 'adb kill-server' if that seems wrong.
Otherwise check for a confirmation dialog on your device.
Error while Installing APK

I've tried restarting ADB as suggested in the output above. Also, I never get a confirmation dialog in the emulator. Emulators for other versions. eg. Nougat 7.1 work fine.

I'm running Android Studio 3.0 Canary 1 (the standard channel doesn't work either).

Answer 1

I've been searching for an answer to this issue, but finally worked it out for myself.

Emulators with "Play Store" enabled are the closest they've ever been to being a real device - including now having to enable Developer Options and then USB debugging to be able to deploy to it. If you don't do this, it shows as being an offline device with unknown capabilities.

https://developer.android.com/studio/debug/dev-options.html

Once the USB debugging option is enabled and the source device is approved, it all springs to life.