Getting an exception when using KVO

I am implementing MKMapView based application. In that 开发者_StackOverflow社区I am using an observer when we tap on a pin. the observer is code is follows,

[annView  addObserver:self
       forKeyPath:@"selected" 
       options:NSKeyValueObservingOptionNew
       context:@"ANSELECTED"];

It is working as expected, but some time it is getting exception 'EXC_BAD_ACCESS'. My log is as follows and it is showing me a leaking memory. Do I need to release the server?. If I ? then where should I release this?

An instance 0x1b21f0 of class MKAnnotationView is being deallocated
while key value observers are still registered with it. Observation
info is being leaked, and may even become mistakenly attached to
some other object. Set a breakpoint on NSKVODeallocateBreak to stop
here in the debugger. Here's the current observation info:

<NSKeyValueObservationInfo 0x11e5f0> (
<NSKeyValueObservance 0x1b1da0: Observer: 0x120f70, Key path: selected, Options: <New: YES, Old: NO, Prior: NO> Context: 0x2b588, Property: 0x1acaa0>

It is working as excepted, but some time it is getting exception 'EXC_BAD_ACCESS'. My log is as follows and it is showing me a leaking memory. …

An instance 0x1b21f0 of class MKAnnotationView is being deallocated while key value observers are still registered with it.

That's the opposite of a leak. It is being deallocated; a leak is when an object will never be deallocated.

The problem is that it's being deallocated while something else is still observing it. Anything that's still observing this object may also send it other messages later; when it does, those messages will go to a dead object (causing the crash you saw, which happened after that message) or to a different object.

If the object that is observing the MKAnnotationView is owning it and releasing it, it needs to remove itself as an observer before releasing it. If it does not own it, it probably should.

You have to stop observing the annotation view before you release it:

[annView removeObserver:self forKeyPath:@"selected"];

I know that it's quite old but I see that this code is used a lot on stackoverflow and in other repositories, and here is a solution to the problem.

You should create an NSMutableArray ivar in your view controller class in order to store a reference to your annotations view:

MyMapViewController <MKMapViewDelegate> {
NSMutableArray *annot;

}

Initialize it in your viewDidLoad and in your - (MKAnnotationView *) mapView:(MKMapView *)theMapView viewForAnnotation:(id <MKAnnotation>) annotation you should add the MKAnnotationView to the mutable array itself right before the annView addObserver code:

 if(nil == annView) {
    annView = [[MyAnnotationView alloc] initWithAnnotation:myAnnotation reuseIdentifier:identifier];
    [annot addObject:annView];
}


[annView addObserver:self
          forKeyPath:@"selected"
             options:NSKeyValueObservingOptionNew
             context:(__bridge void *)(GMAP_ANNOTATION_SELECTED)];

Then, in your viewDidDisappear method you can iterate the array and remove manually all the observers:

    //remove observers from annotation
for (MKAnnotationView *anView in annot){
    [anView removeObserver:self forKeyPath:@"selected"];
}

[annot removeAllObjects];

[super viewDidDisappear:animated];