Android Studio: R.jar: The process cannot access the file because it is being used by another process

Question

After a new installation of Android Studio 3.6.3 (portable). When I try to build and run my project, I keep getting

app\build\intermediates\compile_and_runtime_not_namespaced_r_class_jar\debug\R.jar: The process cannot access the file because it is being used by another process.

Not sure what it wants from me. I run Android Studio "as administrator" and even closing the project and reopening it, the first time it runs, the second time I get the error.

I tried invalidate caches and restart, I tried deleting folders under app/build but it seems to come back. What am I missing?

Thanks

Update:

When trying to clean the project, I get the following

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:clean'.
> Unable to delete directory 'C:\Users\name\Downloads\portable\android-studio\projects\appm\app\build'
    Failed to delete some children. This might happen because a process has files open or has its working directory set in the target directory.
    - C:\Users\name\Downloads\portable\android-studio\projects\appm\app\build\intermediates\compile_and_runtime_not_namespaced_r_class_jar\debug\R.jar
    - C:\Users\name\Downloads\portable\android-studio\projects\appm\app\build\intermediates\compile_and_runtime_not_namespaced_r_class_jar\debug
    - C:\Users\name\Downloads\portable\android-studio\projects\appm\app\build\intermediates\compile_and_runtime_not_namespaced_r_class_jar
    - C:\Users\name\Downloads\portable\android-studio\projects\appm\app\build\intermediates

If I wait for several minutes, for example, the time it took me to update this question, then it works again...

update: Updated to Android Studio 4 and the same problem occurs.

Answer 1

Try

taskkill /im java.exe /f 

in cmd (windows 10)

Answer 2

I encountered the same problem but on Android Studio Arctic Fox while working on a Jet Compose project.

I simply changed the run configuration and the build error was resolved.

Change DefaultPreview to app and the issue is resolved.