问题及原文链接：Error: Unfortunately you can't have non-Gradle Java modules and > Android-Gradle modules in one project

解决方案：

• 1- close the project
• 2- close Android Studio IDE
• 3- delete the .idea directory
• 4- delete all .iml files
• 5- open Android Studio IDE and import the project

shift + cmd + > 可以查看隐藏目录。