Why doesn't Android Studio see the R class?

Question

linux

The studio does not see the R class.

I am sitting under kali linux.
Here is the error:

Exception in thread "png-cruncher_18" java.lang.RuntimeException: Timed out while waiting for slave aapt process, make sure the aapt execute at /home/Android/Sdk/build-tools/23.0.2/aapt can run successfully (some anti-virus may block it) or try setting environment variable SLAVE_AAPT_TIMEOUT to a value bigger than 5 seconds
at com.android.builder.png.AaptProcess.waitForReady(AaptProcess.java:108)
at com.android.builder.png.QueuedCruncher$1 .creation(QueuedCruncher.java:110)
at com.android.builder.tasks.WorkQueue.run(WorkQueue.java:203)
at java.lang.Thread.run(Thread.java:745)

aapt file in place.
Grandel is constantly loading something and apparently doesn't want to stop...

Answer 1

The following helped me:
Tab Build - Clean Project

Answer 2

if you click on the light bulb, will it prompt you to insert the missing import?