Reachability

代码说明：

  iOS 网络状态监测。网络实时检测，用到Reachability（自行下载）,需加框架:SystemConfiguration.framework ios程序需要用到网络检测，有些程序是刚启动时检测一次，而有些则从头到尾检测网络状态。(IOS network status monitoring.Real-time detection and Reachability (download), frame: SystemConfiguration.framework IOS programs need to use network detection, some detection once when the program is launched, while others detect the network status start to finish.)