MKMapView crashes app when view controller popped

Question

I have a view controller with an MKMapView that calls

[self.mapView setRegion:region animated:YES];

which repositions the map from A to B.

The view controller which holds the MKMapView is set as the delegate and in

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated

I have some code that will trigger another setRegion:animated: to the MKMapView so that the map will zoom in on the new position automatically.

Everything works fine if I popViewControllerAnimated: the view controller AFTER the MKMapView animation is done panning and zooming.

However, when I try to popViewControllerAnimated: the current view controller WHILE the MKMapView is running it's animation, the app crashes with "message sent to deallocated instance".

From the looks of the debugger, I think that MKMapView is trying to call a method from a popped and deallocated delegate.

So I tried

[self.mapView setDelegate:nil];
self.mapView = nil;

in viewDidUnload with no luck. The app still crashes consistently.

The only thing I could think of was to create a separate new delegate class and retain that class from the parent view controller so that the MKMapView would have a delegate to call even after the view controller that contains it is deallocated.

Why is this happening? Are there any other "clean" options?

This is interesting. Our app is being crippled by baffling crashes that occur when an MKMapView calls the delegate to get a view for an annotation. The problem is that there IS no MKMapView in existence at that point; or there shouldn't be. The controller containing it has long since been popped. Wonder if it's the same problem. — Oscar, Nov 19 '11 at 02:04
Looks like the same problem as this: http://stackoverflow.com/questions/2188098/why-am-i-crashing-after-mkmapview-is-freed-if-im-no-longer-using-it — Oscar, Nov 19 '11 at 20:08

score 14 · Accepted Answer · answered Sep 02 '11 at 01:26

14

A friend helped me get this one.

I implemented my own method for popping the view controller instead of using the default navigation controller's back button. I just had to add [self.mapView setDelegate:nil]; before I popped the view controller.

- (void)goBack
{
    [self.mapView setDelegate:nil];
    [self.navigationController popViewControllerAnimated:YES];
}

answered Sep 02 '11 at 01:26

Jiho Kang

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3

It wasn't possible to do this in viewWillDisappear? – Oscar Nov 19 '11 at 17:55
1

@Oscar: I was just about to take Jiho's answer then saw your your suggestion. Should work if done in viewWillDisapear. – pnizzle Jan 11 '13 at 06:55

score 8 · Answer 2 · answered Nov 20 '11 at 21:18

OK, this is the real answer. It's from the Apple doc, but it's missing from MKMapView. It's only found under the documentation for its delegate protocol:

"Before releasing an MKMapView object for which you have set a delegate, remember to set that object’s delegate property to nil. One place you can do this is in the dealloc method where you dispose of the map view."

NOTE: This also applies to UIWebView.

I set the MapView's delegate pointer to nil in the delegate's dealloc method, and our crashes seem to have been eliminated.

This applies to _any_ object which may live longer than its delegate. — jscs, Nov 20 '11 at 21:21

score 0 · Answer 3 · answered Nov 21 '15 at 09:45

My problem was not solved by setting delegate of MKMapView to nil in my view Controller

[self.mapView setDelegate:nil];

I had to make a __strong reference of my UIViewController containing MKMapView in my RootViewController.

__strong <#UIViewController#> *vcNewLocation;

score 0 · Answer 4 · answered Apr 25 '19 at 10:19

I had done Clustering and was marking the Annotation selected like so mapView.selectAnnotation(annotation, animated: true).

while popping, the deinit method used to crash.

So on press of back button I just add this line mapView.deselectAnnotation(selectedAnnotation, animated: false) and it solved the crash.

score -1 · Answer 5 · edited Apr 18 '13 at 11:54

-1

The following code is likely to asolve your problem:

-(void) viewWillDisappear:(BOOL)animated
{
    self.mapView.delegate = nil;
    mapView=Nil;
    NSLog(@"viewWillDisappear");

}

edited Apr 18 '13 at 11:54

Lorenzo Dematté

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answered Apr 18 '13 at 11:37

Jasvinder Singh Ranot

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You forgot to call super method of viewWillDisappear:animated – Neru Mar 05 '14 at 12:39

MKMapView crashes app when view controller popped

5 Answers5

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