R file not found problem

Package is used for classification, and remember that the class name should be big hump

When creating an activity in a new subdirectory, the R file will not be found, and R is red

Solution:

Press alt+enter to automatically import the package, or put it in the red place, click more action, and see the recommended processing method for you. Generally, the import package can be solved.

As for why the activity created outside the subdirectory does not have this R import package
Probably because com.xidian.diankan
already contains the R file
and you naturally need to import it in the subdirectory