Question

So I have a method that checks for internet connection, but only during the -(id):init method. Can I set it up so that it constantly checks for connection? If it helps, here is the code:

- (id) checkConnected
    {

        NSError *error = nil;
        NSString *URLString = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com"] encoding:NSASCIIStringEncoding error:&error];
        if (URLString != NULL)
            {
                connected = YES;
            }
        else connected = NO;

        if(connected == YES)
            NSLog(@"Connected");
        else if (connected == NO)
            NSLog(@"NotConnected");

        return self;
    }

Answer 1

While Reachability is a good first-pass check as others have suggested, it only tests the negative case: is it impossible to make a connection? If a firewall is blocking you, or the remote server is down, or any of a thousand other things happens, Reachability might tell you a system is in principle reachable (i.e. you have a network connection and the host if routeable) but the host is not in fact reachable.

So for some applications what you are asking is not unreasonable. The thing you have to be careful about is not to block your main thread with constant tests. Here is some code that will repeatedly run tests in the background:

NSURL *url = [NSURL URLWithString:@"http://www.google.com"];
NSURLRequest *req = [NSURLRequest requestWithURL:url];
__block NSHTTPURLResponse *response = nil;
__block NSError *error = nil;
dispatch_queue_t netQueue = dispatch_queue_create("com.mycompany.netQueue", DISPATCH_QUEUE_SERIAL);
dispatch_async(netQueue, ^{
    while (! [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:&error]) {
        NSLog(@"Connection failed.");
    }
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"Connection succeeded");
    });
});
dispatch_release(netQueue);

Where “Connection succeeded” is logged you could instead write some main thread code that runs when a connection is successful. Note that I am passing in *response and *error from outside the block so they too will be available on your main thread inside or outside the block (assuming you keep them in scope) for your use.

You may want to throttle (i.e. just not use while()), but this is an implementation detail. Using NSTimer() as Richard suggested would work.

Finally, even with this code you still need to handle a potential failure of a subsequent connection. Just because it worked once doesn’t mean the connection is available a millisecond later.