Reachability的示例程序：

https://developer.apple.com/library/ios/samplecode/Reachability/Reachability.zip

不变的：

// 监听网络状态改变的通知

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkStateChange) name:kReachabilityChangedNotification object:nil];

// 创建Reachability

self.conn = [Reachability reachabilityForInternetConnection];

// 开始监控网络(一旦网络状态发生改变, 就会发出通知kReachabilityChangedNotification)

[self.conn startNotifier];

改变的

- (NSString *)networkStateChange{

NSInteger currentStatu = [[Reachability reachabilityForInternetConnection] currentReachabilityStatus];

switch (currentStatu) {

case NotReachable:

return @"无网络";

break;

case ReachableViaWiFi:

return @"Wifi";

break;

case ReachableViaWWAN:

return @"G网";

break;

default:

return @"";

break;

}

}