Unsupported Modules Detected: Compilation is not supported for following modules: app, KeyboardView.

打开AS时出现了Unsupported Modules Detected: Compilation is not supported for following modules: app, KeyboardView. Unfortunately you can’t have non-Gradle Java modules and Android-Gradle modules in one project的错误,解决步骤如下:
(1)关闭as
(2)删除.idea目录
(3)删除app/build目录
(4)重新打开as

from:https://blog.csdn.net/qq_40600379/article/details/106485687