When met with this error in ObjC project while compiling, it means:
Example class is declared by @class in its invoker's class header but not directly #import.
We have 2 ways to solve this problem:
- Directly declare Example class by #import “Example.h” in the header.
- Add a method to return specific Example you want in invoker’s class header. (use this way if you use both ObjC and Swift and Example is a Swift class in a framework project.)