Xcode的#import比#include的好处是解决多重包含的问题，遇到了相互包含头文件的问题
property with ‘retain(or strong)‘ attribute must be of object type”
解决方案就是在出错头文件中实现
@class 文件名;即可解决例如
#import "BaseViewModelService.h"
#import "NavigationImpl.h"
@class NavigationImpl;
@interface BaseViewModel : NSObject
@property(nonatomic,strong) NavigationImpl *naviImpl;
关于iOS开发property with 'retain(or strong)' attribute must be of object type
原文：https://www.cnblogs.com/OIMM/p/10916290.html