找不到符号MainThread，Nullable，WorkerThread

Question

我在这里做了所有操作：Android Studio suddenly cannot resolve symbols，没有任何解决方案可以解决问题

Rebuilding the project
Cleaning the project
Syncing with Gradle Files
Closing the Project, closing AS and relaunching / reopening
File > Invalidate Caches / Restart
Examining Lint, didn't see anything obvious
Double checking all support libraries are up to date in the SDK manager
Examining my Build.gradle, although no changes and it's the same as usual, the way it was working all the time.


Exit Android Studio
Back up your project
Delete all the .iml files and the .idea folder
Relaunch Android Studio and reimport your project

已删除〜/ .AndroidStudioPreview