How to differentiate between screen lock and home button press on iOS5?

Question

I'm developing an iPhone app that plays audio in the background. I want the audio to keep playing if the user locks the screen, but pause if they decide to switch to another app (by pressing the home button).

On iOS 4 there was no problem because the app would go into the inactive state when the screen was locked and only be moved to the background if the home button was pressed. On iOS 5 when the screen is locked the app is now also moved into the background, so it seems it is no longer possible to tell the difference between the two states. Is there a solution to this problem?

Answer 1

You can distinguish these two cases by checking the applicationState property of UIApplication. It will be set to UIApplicationStateInactive for an application that did enter background because of the lock screen, and to UIApplicationStateBackground otherwise.

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    UIApplicationState state = [application applicationState];
    if (state == UIApplicationStateInactive) {
        NSLog(@"Sent to background by locking screen");
    } else if (state == UIApplicationStateBackground) {
        NSLog(@"Sent to background by home button/switching to other app");
    } 
}