判斷是否有開啟網路

先下載這個Library

https://gist.github.com/darkseed/1182373

- (void)viewDidLoad {
    Reachability *internetReach = [[Reachability reachabilityForInternetConnection] retain];
    [internetReach startNotifer];
    Reachability *wifiReach = [[Reachability reachabilityForLocalWiFi] retain];
    [wifiReach startNotifer];

    NetworkStatus netStatus1 = [internetReach currentReachabilityStatus];
    NetworkStatus netStatus2 = [wifiReach currentReachabilityStatus];
    if(netStatus1 == NotReachable && netStatus2 == NotReachable)
    {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Sorry" message:@"This feature requires an internet connection." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alertView show];
        [alertView release];
    }
    else
    {//wifi connection available;
}
}