Programming background behavior when iPhone is locked and user presses power button

Question

Sorry, I am new to iPhone development and my google searches have failed me, so I have had to resort to posting a potentially idiotic question on SO.

I would like to write an app that, when suspended, performs an action when the user presses the home or power button (presumably to unlock the phone). I read the section in the iOS App Programming Guide's App States and Multitasking and the "Processing Queued Notifications at Wakeup Time" discusses handling queued events upon waking up. However, this isn't what I'm after.

I'd like to know if it is possible to:

1. From the phone sleeping state (I couldn't find a document for phone states, so I am talking about the case where the user presses the power button to turn off the screen), I would like my app to be ready to respond to the event where the user presses the power or home button (to unlock the phone)
2. I would like my app to respond to the event that occurs when the user unlocks the phone. I found an answer here that's close.
3. I don't want any funkiness when calls come in, get ignored, etc. :)

From what I can tell, it's a very gray area in the API around locking and unlocking, and I'd like to verify whether or not I'm wasting my time trying to do this.

It looks like I can use the accelerometer to detect when the phone is locked, but I also assume that I won't be able to count on this behavior in all future versions of iOS.

EDIT - I think I can handle the locking and unlocking requirements by assuming that the application has to be running at the time the phone is locked and unlocked, but I still cannot figure out if it is possible to determine #1 above, which is that the power button has been pressed and the unlock screen is displayed. Likewise, I'd like to know if the power button has been pressed again and is no longer displayed (i.e. screen is off).

Answer 1

All of the behaviors for your app being suspended/backgrounded are in the document you referenced. The AppDelegate will receive these messages and pass them on to whatever view you want to listen for them.

-applicationWillTerminate
-applicationWillEnterBackground
-applicationDidBecomeActive
-applicationWillResignActive

You can set up a notification observer in your view if you would like the view to be notified of any of these events. Then just override them or set up a custom method to do any work that needs to be done.

While the Apple docs might be a little foggy at first, all the information is in there to let you know which state your app will go to and how it will be handled. It is up to you to figure out what your app needs to do for each of these events. Hope this helps.