Test if internet connection is available

rhuettl · December 2008

Hi there,

is there a simple piece of code testing if the internet is available on the iPhone - i know the reachability example app but that seems to be a great overhead. So i only like a network test (CFNetwork ?) who can check this - any help available?

Cheers :-)
Ralf

rhuettl · December 2008

Solved it with a example from a book (i hate reading) :-)

NewiPhoneDeveloper · December 2008

There is another way for testing network availability. I have to admit, it's not the nicest one :-)

You could use a hidden UIWebView and load a website to it. Then use methods from the UIWebView.h to detect, whether loading was successful or not.

rhuettl · December 2008

Hi,

hmm that sounds a bit crazy :-)

Here is the code (tested and working fine):

- (BOOL) connectedToNetwork
{
    // Create zero addy
    struct sockaddr_in zeroAddress;
    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.sin_len = sizeof(zeroAddress);
    zeroAddress.sin_family = AF_INET;
	
    // Recover reachability flags
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);
    SCNetworkReachabilityFlags flags;
	
    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
    CFRelease(defaultRouteReachability);
	
    if (!didRetrieveFlags)
    {
        printf(\"Error. Could not recover network reachability flags\n\");
        return 0;
    }
	
    BOOL isReachable = flags & kSCNetworkFlagsReachable;
    BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;
    return (isReachable && !needsConnection) ? YES : NO;
}

Ciao
Ralf

backwardselvis · December 2008

rhuettl;32831 said:
...is there a simple piece of code testing if the internet is available...

Hi Ralf,

What if your iPhone connects to a wireless router, and that router is not connected to the internet? Will your app fail gracefully?

-peace

erotsppa · December 2008

is that code the example from the book?

nownot · January 2009

when i try to implement this i get error's first one being storage size of zeroaddress isnt known, ideas?

ambiensignal · January 2009

I got the same code out of a book and got the same error message as the poster above.

dbrownstone · January 2009

Add the SystemConfiguration framework - also don't forget to
#import
#include

ambiensignal · January 2009

Ah, of course. That was dumb.

ash · January 2009

Hey

the code above doesn't detect cellular network. any idea on how to do that?

Bungler · February 2009

It seems there is a bit of an issue with the above code and it may need to be modified depending upon your intended use. I put this code into my app (original code provided by Apple; thank you Apple) and it only worked when the iPhone was on a WiFi connection. I did some research and testing to come up with a solution.
There are a set of flags that can be used to determine connectivity (iPhone Dev Center). Not being entirely sure which to use, I set up a tester that would show me which flags are active when I am using different connection methods. This is something that I would recommend anyone to try so that you can get a better understanding of how it works, however this is the change I made that seemed to fix the issue:

...
    isReachable = flags & kSCNetworkFlagsReachable;
    needsConnection = flags & kSCNetworkFlagsConnectionRequired;
    [B]nonWiFi = flags & kSCNetworkReachabilityFlagsTransientConnection;[/B]

 [B]return ((isReachable && !needsConnection) || nonWiFi) ? YES : NO;[/B]
...

If someone knows a better way or if im completely wrong here, please let me know.
The problem I am trying to research now is that once the iPhone has left the WiFi connection and gone on to the 3G or Edge networks, it wont go back onto the WiFi again even if I am in range of the signal. I have to exit my app and either wait or reinitialize it in the settings. Does anyone know a way around this?

Bungler · February 2009

OK, I think I have resolved the issue above with some research on this forum. I changed the last IF statement to the following:


...
return ((isReachable && !needsConnection) || nonWiFi) ? 
(([[NSURLConnection alloc] initWithRequest:[NSURLRequest 
requestWithURL: [NSURL URLWithString:@\"http://www.apple.com/\"] 
cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:20.0] 
delegate:self]) ? YES : NO) : NO;
...

What (I think) its doing is after it tests for reachability, it requests data from a www site using NSURLConnection, which makes the iPhone search for connections. Sorry for my non-technical explanations :)

EDIT: I changed the cache policy to not pull from the local cache so that it looks for the page every time. In my code, I also am not using apple.com as the request URL. I put up a simple html page on my server with the word 'true' in it and I am requesting that page for the connection testing. Keeping the request small might help the load time, even if you are doing nothing with the requested data. Even a 404 returns something.

mpramodjain · February 2009

Hi all,

This is very very good thread ,,atmost usefulllll..
but unable to understand , what does the zeroaddress contains..Any link on web would be help ful for understanding this..
Thank u all.

dbrownstone · February 2009

mpramodjain;53058 said:
Hi all,

This is very very good thread ,,atmost usefulllll..
but unable to understand , what does the zeroaddress contains..Any link on web would be help ful for understanding this..
Thank u all.

The zero address is simply 0.0.0.0 - I in fact, chose to use apple.com to check for connectivity ...[self hostAvailable:@"www.apple.com"]....

wynodir · March 2009

If the code in any case connects to a web server to try if there's a connection, why not just do this:


- (BOOL) connectedToNetwork
{
   return ([NSString stringWithContentsOfURL:[NSURL URLWithString:@\"http://www.myserver.com/smalltext.txt\"]]!=NULL)?YES:NO;
}

This function will return NO if it cannot reach the file. Otherwise, it will return YES. I tried it in flight mode and in 3G mode. It works.

Ben. · March 2009

Wynodir: How does ur suggestion handle timeouts?

I tested it this way but my application will just wait and wait and wait and wait... I need to set a timeout. Can u tell me how?

EDIT: What datatype is this nonWifi?

sirjec · November 2009

The Reachability sample code is what you should be looking at here. Although the class it uses is almost 1000 lines long, it shows you how it all works. I'm about to start picking through it all for what I need:p

redon · November 2009

wynodir;62798 said:
If the code in any case connects to a web server to try if there's a connection, why not just do this:
- (BOOL) connectedToNetwork
{
   return ([NSString stringWithContentsOfURL:[NSURL URLWithString:@\"http://www.myserver.com/smalltext.txt\"]]!=NULL)?YES:NO;
}
This function will return NO if it cannot reach the file. Otherwise, it will return YES. I tried it in flight mode and in 3G mode. It works.

i tryed the following code, put my iphone in airplane mode and ran the app. it appears to not work...at all

- (BOOL) connectedToNetwork {
	return ([NSString stringWithContentsOfURL:[NSURL URLWithString:@\"http://www.apple.com/\"]]!=NULL)?YES:NO;
	
	if (YES) {
	}
	
	if (NO) {
		UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@\"no internet connection\" 
													   delegate:self cancelButtonTitle:@\"OK\" otherButtonTitles:nil];
		[alert show];
	    [alert release];
	}
}

Steaps · November 2009

redon;143532 said:

i tryed the following code, put my iphone in airplane mode and ran the app. it appears to not work...at all

- (BOOL) connectedToNetwork {
	return ([NSString stringWithContentsOfURL:[NSURL URLWithString:@\"http://www.apple.com/\"]]!=NULL)?YES:NO;
	
	if (YES) {
	}
	
	if (NO) {
		UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@\"no internet connection\" 
													   delegate:self cancelButtonTitle:@\"OK\" otherButtonTitles:nil];
		[alert show];
	    [alert release];
	}
}

Nothing after the return statement is being called. Try using NSLog() to see where code ends/if it's called.

ziophase · December 2009

I like the idea of loading a small string from the web. I tested it on the simulator and the following code works fine if my internet is connected or not connected. I gave it a 2 second timeout...


-(void)viewDidAppear:(BOOL)animated {
	NSString *connected = [NSString stringWithContentsOfURL:[NSURL URLWithString:@\"http://www.mysite.com/smallfile.php\"]];
	wait(20000);
	if (connected == NULL) {
		NSLog(@\"Not connected\");
	} else {
		NSLog(@\"Connected - %@\",connected);
	}
}

EDIT: Tested it on the device as part of a much bigger app. Works as expected in flight mode / normal connection. If you want to increase the timeout perhaps it might be worth it, but it's working fine for me!

rocotilos · January 2010

Holy cow! You guys are awesome.
Thanks for the code ziophase.

KennyChong · January 2010

rhuettl;32831 said:
Hi there,

is there a simple piece of code testing if the internet is available on the iPhone - i know the reachability example app but that seems to be a great overhead. So i only like a network test (CFNetwork ?) who can check this - any help available?

Cheers :-)
Ralf

Two methods I tried. Reachability is still the best for me. It detect even changes from WifI to 3G to EDGE, etc...

Easier to use method is the UIWebView protocol itself. Hope the code below helps.

#pragma mark UIWebView delegate methods

- (void)webViewDidStartLoad:(UIWebView *)webView
{
// starting the load, show the activity indicator in the status bar
[myActivityIndicatorView startAnimating];
}

- (void)webViewDidFinishLoad:(UIWebView *)webView
{
[myActivityIndicatorView stopAnimating];
}

- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error
{
int myErrorCode;

[myActivityIndicatorView stopAnimating];

myErrorCode = [error code]; // myErrorCode = -999 if user cancel action, not network problem
if (ckErrorCode != -999)
{
// Your error handling code here
NSLog(@"UIWebView Load Failed-Error");
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Connection Error!" message:@"Unable to connect to the website." delegate:self cancelButtonTitle:nil otherButtonTitles:@"OK", nil];
[alert show];
}
}

// #pragma mark UIWebView delegate methods

rocotilos · January 2010

Whoa KennyChong, Another fellow countryman. :D

ziophase · January 2010

rocotilos;164505 said:
Holy cow! You guys are awesome.
Thanks for the code ziophase.

There's a much better way to do it!

Download the apple sample code reachability.

Then follow the steps listed in post 29 here:

http://www.iphonedevsdk.com/forum/iphone-sdk-development/19546-no-wifi-connection-best-practice-2.html#post118631

Cheerio

mirap · February 2010

Hi!
I read all the posts here and there is currently no working solution for setting timeout. Fe.: wait(20000); writes "Passing argument 1 of wait makes pointer from integer without a cast"...

Is there any way how to create timeout for:

- (BOOL) connectedToNetwork
{
return ([NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com"] encoding:NSASCIIStringEncoding error:nil]!=NULL)?YES:NO;
}
?

Thanks a lot.

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