R file in Android studio turns red and error

Last night came across a very puzzling question, want to share, hope to help you.

The previous use of studio R files is not an error. When you copy some code from another program, you will find that the R file turns red and the application does not run. There are no errors except the R file, and only the app is running with an error.

This is because when you copy some code from another program. Your r file does not automatically load and you need to remove the error code and re-enter it in Android studio so your application can run.

R file in Android studio turns red and error