`cb?.let {}` in andriod studio, give me error tip...

# android

[ngubenson]

cb?.let {} in andriod studio, give me error tip: unresolved reference: let. But I can build it successfully by gradle. I use kotlin in my old java project. Any body knows why?

[pablisco]

Have you tried invalidate and restart?

[ngubenson]

I restarted android studio twice, and made it. Thank you. @pablisco