最近项目中用到了AFNetworking，在iOS 6.0以上版本编译时可以正常运行，但在低于iOS 6.0的版本编译时，会编译失败，主要是报以下错误：
Property with 'retain (or strong)' attribute must be of object type
主要涉及AFURLConnectionOperation.h和AFURLSessionManager.h两个文件，由于低于iOS 6.0时，dispatch_queue_t ARC没有托管，所以会出现这样的情况。
解决如下
#if OS_OBJECT_USE_OBJC @property (nonatomic, strong) dispatch_queue_t completionQueue; #else @property (nonatomic, assign) dispatch_queue_t completionQueue; #endif
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