Android studio error message:
To solve the problem, see the picture below:
Other learning materials:
1. Paid column "Android kotlin entry to advanced series of explanations": https://blog.csdn.net/qq_35091074/category_11036895.html
2. Free column "Android kotlin open source project-function" (source code available) ): https://blog.csdn.net/qq_35091074/category_12005202.html