AFNetworking 2.0 当Deployment Target 低于6.0时，AFURLConnectionOperation.h,AFURLSessionManager.h
@property (nonatomic, strong) dispatch_queue_t completionQueue;
由于sdk低于6.0时，dispatch_queue_t ARC没有托管，出现提示错误
Property with ‘retain (or strong)‘ attribute must be of object type
修改为
#if OS_OBJECT_USE_OBJC
@property (nonatomic, strong) dispatch_queue_t completionQueue;
#else
@property (nonatomic, assign) dispatch_queue_t completionQueue;
#endif
/**
The dispatch group for `completionBlock`. If `NULL` (default), a private dispatch group is used.
*/
#if OS_OBJECT_USE_OBJC
@property (nonatomic, strong) dispatch_group_t completionGroup;
#else
@property (nonatomic, assign) dispatch_group_t completionGroup;
#endif
AFNetworking编译报错 Property with 'retain (or strong)' attribute must be of object type
原文：http://www.cnblogs.com/shnuzxw/p/4359767.html