AFNetworking 2.0 ERROR:Property with 'retain (or strong)' attribute must be of object type [duplicate]

Question

Updated my project to AFNetworking, Xcode show this error:

@property (nonatomic, strong) dispatch_queue_t completionQueue;

Property with 'retain or strong' attribute must be of object type.

I cannot understand why the official example there is no error warning?

Answer 1

I get it, because I test on iOS5, dispatch_queue_t is objcet begin at iOS6