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