每当我尝试使用命令清理我的颤振项目时，
flutter clean我都会收到一条错误消息
Failed to remove build. A program may still be using a file in the directory or the directory itself. To find and stop such a program, see:
https://superuser.com/questions/1333118/cant-delete-empty-folder-because-it-is-used
我可以理解打开了一些目录，它必须关闭才能清理。但我无法理解它是哪一个。我尝试重新启动计算机以解决此问题。但是当我运行命令flutter clean时，我仍然收到错误。