// 异步线程做耗时操作
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0)) { () -> Void in

            // 主线程更新UI
            dispatch_async(dispatch_get_main_queue(),{ () -> Void in
                
                
            })
        }

学自:http://www.jianshu.com/p/2598a4e9c139