Update the next idea, the results of the project can not find a lot of class, suggesting that "can not resolve symbol", but can function properly.
Many online solution is to reduce the idea to check the level, but raises another problem, if it lacks class, there would be an error.
In fact, under the idea as long as the clear cache and restart under it.
Specifically: Click on the menu "File" -> "Invalidate Caches / Restart" → "Invalidate and Restart", empty the cache and reboot .
problem solved.
end !!
