Yesterday I have Updated my android studio, since then auto completion and error detection is not working.

Solution 1: Varun Kumar

Try resetting Android Studio settings. Close Android Studio, locate and delete this folder (copy to another location before deleting, so you can return to it if something goes wrong).

C:\Users<Your User>\AppData\Roaming\Google\AndroidStudio< version >

This should reset your Android Studio settings to default. Now check if auto-complete and error detection works or not.

Solution 2: Carlos P.

First close Android Studio.

On mac just go to ~/Library/Application Support/Google/

And delete all the AndroidStudio< version > folders, after this you will see the errors.