enable Annotation Processors option in Android Studio 2.2

You can enable Annotation Processors without closing your project in Android Studio 2.3:

File -> Other Settings -> Default Settings

Build, Execution, Deployment -> Compiler -> Annotation Processors -> 
Enable annotation processing.

Don't forget to clean, build, invalidate and restart after that.
Cheers!

1. Close all your AndroidStudio Project

2. See

3. Click Configure-->Setting See

Close the project. In the "Welcome to Android Studio" dialog click "Configure" in the bottom right corner.

Then,

Settings > Build, Execution, Deployment > Compiler > Annotation Processors. Tick 'Enable annotation processing'.

If that does not work. Delete the project from "Welcome to Android Studio" dialog and open from new.

Worked for me.