KVO lost when entering background, trying to fix - ios

Question

I have this method, adding an observer in myViewController:
-(void) observeSpeakerVolume{
[[AVAudioSession sharedInstance] setActive:YES error:nil];
[[AVAudioSession sharedInstance] addObserver:self forKeyPath:#"outputVolume" options:NSKeyValueObservingOptionNew context:nil];
}
I invoke this method in the viewdidLoad of myViewController:
- (void)viewDidLoad {
[self performSelectorInBackground:#selector(observeSpeakerVolume) withObject:nil];
[super viewDidLoad];
}
and finally I monitor the observer as follows:
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
if ([keyPath isEqualToString:#"outputVolume"]) {
if ([[change valueForKey:#"new"] isEqualToNumber:#0]){
...
} else {
...
}
}
}
This all works fine, but as soon as my app is send to the background, eg by hitting the home button, the observer seems to be automatically removed.
To fix that, I do this in my AppDelegate:
- (void)applicationWillEnterForeground:(UIApplication *)application {
myViewController * wfc = [[myViewController alloc]init];
[wfc observeSpeakerVolume];
}
That seems to work, however, switching back and forth several times between back- and foreground, eventually changing the volume of my iPhone crashes the app.
I tried to manually remove the observer when entering the background, but that also crashes the app, supporting the suggestion that the OS removes the observer automatically when entering the background.
So, I assume, that I'm adding the observer several times, but I don't see where, since ViewDidLoad is not called when the app enters the foreground.
What is wrong in my logic here?
thanks for your insights.

Answer 1

Bit late, but I had similar issue.
If you call
[[AVAudioSession sharedInstance] setActive:YES error:nil];
after your app is back from background e.g. in
- (void)applicationWillEnterForeground:(UIApplication *)application;
then the observer will work again.