Android studio design editor is unavailable until after a successful project sync

Question

what is the actual root cause of this issue? I already sync with gradle files but eventually failed.

Answer 1

Issue happened to me when I changed the res>values>styles.xml

What I change was
"Theme.AppCompat.Light.DarkActionBar" --->>> "Base.Theme.AppCompat.Light.DarkActionBar"

Solutions I tried.

1. Build -> Rebuild Project (Not worked)
2. Close all files and Open again. Then Build -> Clean Project (Not worked) File -> Sync project with gradle files (Not worked)
3. Close the Android Studio while project still opened. Opened it again. - It Worked.