How to find out which other UIScrollView interferes with scrollsToTop?

Question

I have several view controllers with one or multiple scrollviews. Although I have explicitly set the scrollsToTop flags in view controllers with more than one scroll view, some scroll views refuse to scroll up when I tap the status bar.

After pushing another view controller and popping it the gesture sometimes works in the view it previously hasn't.

It's very confusing and I just don't know what the problem is. How can this issue effectively be debugged? Is there a global (private) notification for the status bar tap so I could scroll the views manually?

score 22 · Accepted Answer · answered Jul 16 '12 at 16:25

I have used code like the following to debug this scenario, before:

- (void)findMisbehavingScrollViews
{
    UIView *view = [[UIApplication sharedApplication] keyWindow];
    [self findMisbehavingScrollViewsIn:view];
}

- (void)findMisbehavingScrollViewsIn:(UIView *)view
{
    if ([view isKindOfClass:[UIScrollView class]])
    {
        NSLog(@"Found UIScrollView: %@", view);
        if ([(UIScrollView *)view scrollsToTop])
        {
            NSLog(@"scrollsToTop = YES!");
        }
    }
    for (UIView *subview in [view subviews])
    {
        [self findMisbehavingScrollViewsIn:subview];
    }
}

Depending on how many UIScrollViews you find, you can modify that code to help debug your particular situation.

Some ideas:

Change the background colors of the various scrollviews to identify them on screen.
Print the view hierarchy of those scrollviews to identify all of their superviews.

Ideally, you should only find a single UIScrollView in the window hierarchy that has scrollsToTop set to YES.

Although I cannot test this solution atm, the reasoning is sound. — , Jul 16 '12 at 16:41

score 1 · Answer 2 · edited Jul 31 '21 at 04:36

I changed the accepted answers into swift for convenience:

Swift 5

func findMisbehavingScrollViews() {
    let topView = UIApplication.shared.windows.first { $0.isKeyWindow }
    findMisbehavingScrollViewsIn(topView!)
}

func findMisbehavingScrollViewsIn(_ topView: UIView) {
    if let topView = topView as? UIScrollView {
        if topView.scrollsToTop {
            print("Found UIScrollView: \(topView)")
        }
        for nextView in topView.subviews {
            findMisbehavingScrollViewsIn(nextView)
        }
    }
}

How to find out which other UIScrollView interferes with scrollsToTop?

2 Answers2

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