有关信息NSURLConnection and NSURLSession看到网址
加载系统编程指南。 https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/URLLoadingSystem/URLLoadingSystem.html
查找自参考文献1 https://stackoverflow.com/questions/15718998/asihttprequest-vs-afnetworking-vs-nsurlrequest and 参考文献2 https://stackoverflow.com/questions/28105504/what-is-the-biggest-difference-between-nsurlconnection-and-nsurlsession
Thank rob https://stackoverflow.com/users/1271826/rob and dgatwood https://stackoverflow.com/users/1564391/dgatwood对于如此令人惊奇的答案...