How to call method/code when app is paused in iOS - ios

Question

As the title reads; I am currently playing a sound file on loop using this code:
NSString *soundFilePath = [[NSBundle mainBundle] pathForResource:#"smoothjazz" ofType:#".mp3"];
NSURL *soundFileURL = [NSURL fileURLWithPath:soundFilePath];
player = [[AVAudioPlayer alloc] initWithContentsOfURL:soundFileURL error:nil];
NSFileManager *filemgr = [NSFileManager defaultManager];
if ([filemgr fileExistsAtPath:soundFilePath])
{
// Your code to play the sound file
[player setVolume:1.0];
player.numberOfLoops = 5; //infinite
[player play];
}
However, the music keeps playing when you pause the app (hit the home button). How can I call [player setVolume:0.0] when the app is paused and [player setVolume:1.0] when it is resumed?
All help appreciated.

Answer 1

You can use NSNotificationCenter to listen to the UIApplicationWillResignActiveNotification and UIApplicationDidBecomeActiveNotification notifications in your view controller (or whatever object your above code is in) and the pause/resume playing you sounds there.
You should probably not set the volume on your player. It would probably be better to call
[player pause] and [player play]

Answer 2

There is a protocol that handles state change: UIApplicationDelegate. The ones you are interested in right now are willResignActive and didBecomeActive.
Note that these are not didEnterBackground and willEnterForeground. The difference is the former will get hit when apps takeover, such as Siri, and the latter will not.
You can implement this protocol in your audio manager class and set the volume at that point, like so:
- (void)applicationWillResignActive:(UIApplication *)application {
self.currentVolume = self.player.volume;
self.player.volume = 0;
}
- (void)applicationDidBecomeActive:(UIApplication *)application {
self.player.volume = self.currentVolume;
}
There may be no need to store the current volume, but designing on it to be used like that now will allow you to implement that in the future.
You should consider whether or not you want to mute the player or pause it. I'm sure you have, but a general better practice here would be to pause it rather that mute it, but that's not something that applies to every situation.
Additionally, you should know that some programmers are of the school of thought that only the AppDelegate should implement the UIApplicationDelegate protocol. There's some good arguments for it, and personally, I'm not really decided on what's best practice on that, but if you want to follow that, then you can either set up a protocol to delegate these in your AppDelegate and have your audio manager implement that delegate or you can use NSNotificationCenter to broadcast the event to any listeners - so, your audio manager in this case. Of the two, I would say using notifications is a cleaner way to handle it (delegating to delegates is a bit silly to me), but they also can get messy if you're not careful.

Answer 3

Here's the code I added to the viewDidLoad to call the method on the app pausing:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(muteMusic)
name:UIApplicationWillResignActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(activateMusic)
name:UIApplicationDidBecomeActiveNotification object:nil];
Then, of course, my two methods:
- (void) muteMusic {
[player pause];
}
- (void) activateMusic {
[player play];
}
Enjoy!