这里定义的是C的类型数据。直接在文件中加入#import <UIKit/UIKit.h>解决

I had the same issue on my project when I was trying to mix C code (.h and .c) with Objective-C code. Found the reason of the issue:

Check your .pch file to make sure every Objective-C framework #import (such as #import <UIKit/UIKit.h>) is enclosed in:

#ifdef __OBJC__#endif

iOS中遇到Unkown type name NSString Unkown type name CGFloat