How to correctly use Apples Reachability class to tell if the internet works?

Question

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Are there more sophisticated alternatives to Apples Reachability class?

Here's an example:

Reachability *reachability = [Reachability reachabilityForInternetConnection];    
NetworkStatus internetStatus = [reachability currentReachabilityStatus];
if (internetStatus != NotReachable) {
    // Internet is reachable. Start download in background.
} else {
    // Create UIAlertView and tell user there is no functional internet!
}

Problem: I've heard that in some cases WiFi "may require a connection for VPN on Demand". So how am I supposed to correctly notify the user about a non-functional internet connection? I assume that the code above is not enough to deal with this.

You probably need an access to a certain host. If so, you can always restrain yourself to checking if that certain host is reachable or not. — Rok Jarc, May 29 '12 at 16:09
Yes, [here](http://stackoverflow.com/questions/8812459/easiest-way-to-detect-a-connection-on-ios) is a nice example on how to use Reachability (also) for checking if a certain host is reachable. — Rok Jarc, May 29 '12 at 16:56

score 6 · Accepted Answer · answered May 29 '12 at 16:46

Here is what I usually do, I didn't try it on VPN though! I create a standalone class for the checking the connection, say it is named WifiCheckClass.

In the .h file of the class:

#import <Foundation/Foundation.h>
#import "SystemConfiguration/SCNetworkReachability.h"

@interface UIDevice (DeviceConnectivity)
+(BOOL) cellularConnected;
+(BOOL) wiFiConnected;
+(BOOL) networkConnected;
@end

In the .m file:

#import "WiFiCheckClass.h"

@implementation UIDevice (DeviceConnectivity)

+(BOOL) cellularConnected
{
    SCNetworkReachabilityFlags  flags = 0;
    SCNetworkReachabilityRef netReachability;
    netReachability = SCNetworkReachabilityCreateWithName(CFAllocatorGetDefault(), [@"www.google.com" UTF8String]);
    if(netReachability)
    {
        SCNetworkReachabilityGetFlags(netReachability, &flags);
        CFRelease(netReachability);
    }
    if(flags & kSCNetworkReachabilityFlagsIsWWAN) return YES;
    return NO;
}

+(BOOL) networkConnected
{
    SCNetworkReachabilityFlags flags = 0;
    SCNetworkReachabilityRef netReachability;
    BOOL  retrievedFlags = NO;
    netReachability = SCNetworkReachabilityCreateWithName(CFAllocatorGetDefault(), [@"www.google.com" UTF8String]);
    if(netReachability)
    {
        retrievedFlags  = SCNetworkReachabilityGetFlags(netReachability, &flags);
        CFRelease(netReachability);
    }
    if (!retrievedFlags || !flags) return NO;
    return YES;
}

+(BOOL) wiFiConnected
{
    if ([self cellularConnected]) return NO;
    return [self networkConnected];
}

@end

Now using it is very straight forward:

if( [UIDevice wiFiConnected] || [UIDevice networkConnected] || [UIDevice cellularConnected] )
{
    //do what you want
}

Won't `SCNetworkReachabilityGetFlags` call [block the thread if it cannot reach the DNS server](http://stackoverflow.com/a/4610200/458193)? — Dan Abramov, Mar 14 '13 at 14:45
No, it returns the currently known status immediately. The status may change, so you should listen for notifications. — gnasher729, Jun 03 '16 at 14:42

How to correctly use Apples Reachability class to tell if the internet works?

1 Answers1