In an android application we can use kt or java class but both must have an import R file. Create new activity automatically import R file otherwise manually Alt + Enter to import file. R stands for the resource. This error occurs because of the incapability to build the project .
Most common error is “R can not be resolved” error appears if there is an issue with some of your resource files. you are unable to build this project on mobile application
Method 1
Try the sync Gradle .Just follow this path File > Sync project with Gradle files.
Method 2
Make sure your package name is correct in AndroidManifest.xml Sometime R file not generated of package name in Android Manifest does not match with module package name.
Method 3
Step 1: Clean the project
To clean project : Click on build > clean project
Step 2: Rebuild project
Click on Build and click on rebuild project.
Method 4: Try Invalidate caches and restart file > Invalidate caches/restart
Happy coding!