刚开始建项目 会出现 Version 28 (intended for Android Pie and below) is the last version of the legacy support library, so we recommend that you migrate to AndroidX libraries when using Android Q and moving forward. The IDE can help with this: Refactor > Migrate to AndroidX... less... (Ctrl+F1） 等等字样，修改方法：targetSDKversion 改成 28 就行了
