How to tell with Objective-C if the iPhone is connected to a wifi network?
As others mentioned, the Reachablity sample is a good place to start, however, their answers don't spell it out enough for my tastes. Within the Reachablity sample the code is spread out and doesn't show you how to handle the simplest case. For the simplest case (not listening to changes in state) I can save you the effort of having to collate the right lines yourself.
Copy the Reachability class from the Reachablity sample into your project, include it in your class, and use the following code:
if ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != ReachableViaWiFi) { //Code to execute if WiFi is not enabled}
Look at the Reachability sample provided by Apple in the developer site. It does this.