ios - Is it possible to distinguish between locking the device and sending an app to background?

Question

I have an app that needs to do something when it’s sent to background using the Home button and something else when the device is locked using the top hardware button. The standard way of solving these requirements are the notifications and delegate methods sent out by UIApplication. On iOS?4 they look like this:

// Pressing the home button
Will resign active.
Did enter background.
// Tapping app icon on Springboard
Will enter foreground.
Did become active.

// Pressing the lock button
Will resign active.
// Unlocking the device
Did become active.

In other words, it’s quite easy to tell between locking and backgrounding. On iOS?5 the behaviour changed:

// Pressing the home button
Will resign active.
Did enter background.
// Tapping app icon on Springboard
Will enter foreground.
Did become active.

// Pressing the lock button
Will resign active.
Did enter background.
// Unlocking the device
Will enter foreground.
Did become active.

Notice that the didEnterBackground and willEnterForeground notifications are now sent out even when (un)locking the device, making it impossible to tell between locking and backgrounding. Is this change documented somewhere? Is it a regression? Do you know another way to distinguish the two cases?

Answer 1

iOS 6

In my preliminary testing via the simulator, checking the application state with

[[UIApplication sharedApplication] applicationState]

in either

- (void)applicationWillEnterForeground:(UIApplication *)application

- (void)applicationDidEnterBackground:(UIApplication *)application

allows you to differentiate between a call to lock the device and just switching back to the homescreen. A lock screen will return 1 (UIApplicationStateInactive), whereas a home button press will register as a 2 (UIApplicationStateBackground).

It seems consistent and should work on an iOS device just as reliably as it does in the simulator.

iOS 7

The iOS 6 method no longer works in iOS 7. In order to do this now, you have to utilize CFNotificationCenter and listen for a darwin notification (labeled: com.apple.springboard.lockcomplete). You can find the github repo with the sample project here: https://github.com/binarydev/ios-home-vs-lock-button

Credit for the iOS 7 fix goes out to wqq