Question

My iPad app crashes when you scroll the UIImagePickerController popover, either the PhotoLibrary or PhotosAlbum variety. I have about 130 images in the album and the crash occurs when you scroll the list to bring additional thumbnails into view. I found some other mentions of UIImagePicker issues in the simulator in iOS 2.x here, but that does not seem relevant. Here’s the crash report:

2011-10-07 11:18:17.309 Experiences[1419:707] *** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSArrayM: 0x343fe0> was mutated while being enumerated.(
    "<PLImageTableSegment: 0x343fc0>",
    "<null>",
    "<null>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>",
    "<PLImageTableSegment: 0x343fc0>"
)'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x319b864f __exceptionPreprocess + 114
    1   libobjc.A.dylib                     0x34af4c5d objc_exception_throw + 24
2   CoreFoundation                      0x319b7edf __NSFastEnumerationMutationHandler   + 214
    3   libobjc.A.dylib                     0x34afb36d objc_enumerationMutation + 24
    4   CoreFoundation                      0x31922b9d -[__NSArrayM dealloc] + 80
5   CoreFoundation                      0x3191cc43 -[NSObject(NSObject) release] + 30
6   PhotoLibrary                        0x3733ba81 +[PLImageTable releaseSegmentCache] + 20
7   PhotoLibrary                        0x3732a4ed -[PLPhotoLibrary dealloc] + 116
8   CoreFoundation                      0x3191cc43 -[NSObject(NSObject) release] + 30
9   CoreFoundation                      0x3191d1a1 CFRelease + 68
10  CoreFoundation                      0x3191febb _CFAutoreleasePoolPop + 146
11  Foundation                          0x30efe1cb -[NSAutoreleasePool release] + 98
12  UIKit                               0x36f0ff0f _UIApplicationHandleEvent + 5790
13  GraphicsServices                    0x35a10e77 PurpleEventCallback + 666
14  CoreFoundation                      0x3198fa97 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 26
15  CoreFoundation                      0x3199183f __CFRunLoopDoSource1 + 166
16  CoreFoundation                      0x3199260d __CFRunLoopRun + 520
17  CoreFoundation                      0x31922ec3 CFRunLoopRunSpecific + 230
18  CoreFoundation                      0x31922dcb CFRunLoopRunInMode + 58
19  GraphicsServices                    0x35a1041f GSEventRunModal + 114
20  GraphicsServices                    0x35a104cb GSEventRun + 62
21  UIKit                               0x36f3ad69 -[UIApplication _run] + 404
22  UIKit                               0x36f38807 UIApplicationMain + 670
23  Experiences                         0x00002e77 main + 82
24  Experiences                         0x00002e20 start + 40
)
terminate called after throwing an instance of 'NSException'

And here’s the code that invokes the UIImagePickerController popover:

- (void)showImagePickerForSourceType:(UIImagePickerControllerSourceType)sourceType
{
    if ([self.cameraPopoverViewController isPopoverVisible]) {
        DLog(@"requesting cameraPopover dismissal");
        [self.cameraPopoverViewController dismissPopoverAnimated:YES];
    }

    // Set up the imagePicker common parameters
    UIImagePickerController* imagePicker    = [[UIImagePickerController alloc] init];
    imagePicker.delegate                    = self;
    imagePicker.mediaTypes                  = [NSArray arrayWithObjects:(NSString *) kUTTypeImage, nil];
    imagePicker.allowsEditing               = YES;
    imagePicker.sourceType                  = sourceType;
    DLog(@"imagePicker %@", imagePicker);

    self.newMedia = NO;

    switch (imagePicker.sourceType) {
        case UIImagePickerControllerSourceTypeCamera: {
            [self presentModalViewController:imagePicker
                                    animated:YES];
            self.newMedia = YES;
            break;
        }
        case UIImagePickerControllerSourceTypePhotoLibrary: 
            // These two cases are identical, just fall through into PhotosAlbum case...
        case UIImagePickerControllerSourceTypeSavedPhotosAlbum: {
            if (self.pickerPopoverViewController) {
                // Should never occur if pickers are getting dismissed properly...
                ALog(@"had a stranded pickerPopover!");
                self.pickerPopoverViewController = nil;
            }
            pickerPopoverViewController = [[UIPopoverController alloc] initWithContentViewController:imagePicker];
            // Set up the rect from which the popover should hang
            CGRect popoverRect = [cameraBtn convertRect:cameraBtn.bounds
                                                 toView:self.view];
            // ...and display the popover "hanging" from the cameraBtn
            [self.pickerPopoverViewController presentPopoverFromRect:popoverRect
                                                              inView:self.view 
                                            permittedArrowDirections:UIPopoverArrowDirectionUp
                                                            animated:YES];            
            break;
        }

        default:
            break;
    }
    [imagePicker release];
}

It looks to me like some of the image/imageThumbnails are getting deallocated, (and hence mutating the collection). But I don’t know what to do about it…

Answer 1

I just encountered similar problem.
By trial and error, I found out that if you use UIImagePickerControllerSourceTypePhotoLibrary as the imagepicker’s source type, it will work ok.
But using UIImagePickerControllerSourceTypeSavedPhotosAlbum will crash the app.