标签：http com art os html htm
http://www.appcoda.com/background-transfer-service-ios7/
http://www.raywenderlich.com/51127/nsurlsession-tutorial
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/URLLoadingSystem/Articles/UsingNSURLSession.html
ios后台传输机制,布布扣,bubuko.com
ios后台传输机制
原文地址：http://www.cnblogs.com/trying/p/3790501.html
