Question

I need to create a number of UIScrollViews dynamically and fill them with content. This is all good except when i set the delegate to self and pan the list i get this exception:

Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[__NSCFString scrollViewDidScroll:]: unrecognized selector sent to instance 0x7581230’

NSCFString obviously isn’t my view controller (which implements the protocol UIScrollViewDelegate) so from what i gather somehow the memory gets messed up and it doesn’t keep the reference correctly. Occasionally this can be something else too which strongly points to something being wrong with the memory

Here’s the code to create the list:

for (NSUInteger i = 0; i < self.stories.currentStory.selectableWordCount; i++) {
    UIScrollView *list = [[UIScrollView alloc] init];
    list.alwaysBounceVertical = YES;
    list.showsVerticalScrollIndicator = NO;
    list.clipsToBounds = NO;
    list.delegate = self;
    list.pagingEnabled = YES;
    [self.view addSubview:list];

    .. // add UILabels to the list, set the frame, contentSize etc

    [self.wordLists addObject:list]; // this is a @property (nonatomic, strong) NSMutableArray, declared in a private interface()
}

If i NSLog the delegate it’s correct. respondsToSelector also matches fine. Interestingly if i comment out the scrollViewDidScroll: respondsToSelector: doesn’t match any more and (probably because of this) the UIScrollView won’t attempt to call this method any more. This then means that it can reach the delegate correctly to check for the method availability but when it gets called something goes wrong.

I’m targeting iOS5 with ARC. If this wasn’t the case i would assume that i messed something up with the memory myself but now i don’t have the same control.

I’m having a hard time debugging this issue, any help on how to proceed would be appreciated

Answer 1

D’uh. I was obviously looking in the wrong place. The view controller was added through a .xib and the view was pointing to a subview on the stage. However i needed to create an IBOutlet to the view controller in the main view controller to make sure it stays in memory. Hopefully this can help somebody else with a similar problem 🙂