iOS - UIScrollView不会更新其内容，并且一些UIViews在重新加载后会消失

Question

I have UITableViewController with UIScrollView inside UIView as its header. UIScrollView is used to display slideshow of images:

UITableView
 -UITableViewHeaderView
   -UIView
      -UIScrollView
        -UIImageView
          ...
      -UIPageControl

Every image has a subview with its title and description:

UIImageView
  -UIView
    -UILabel
    -UILabel

When I need to update my tableView a delegate method is called which reloads data in a tableView and calls addImages method:

- (void)eventsUpdated
{
    if ([self respondsToSelector:@selector(setRefreshControl:)])
        [self.refreshControl endRefreshing];

    [self.tableView reloadData];
    [self addImages];
}

Here is how I add my images:

- (void)addImages
[self.scrollView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];

    for (int i = 0; i < images.count; i++) {
        CGRect frame;
        frame.origin.x = self.scrollView.frame.size.width * i;
        frame.origin.y = 0;
        frame.size = self.scrollView.frame.size;

        UIImageView *subview = [self createImageViewForEvent:[images objectAtIndex:i] inFrame:frame];
        subview.frame = frame;
        [self.scrollView addSubview:subview];
    }

    self.scrollView.contentSize = CGSizeMake(scrollView.frame.size.width*images.count, scrollView.frame.size.height);
    pageControll.currentPage = 0;
    pageControll.numberOfPages = images.count;

}

- (UIImageView *)createImageViewForEvent:(Event *)event inFrame:(CGRect)frame
{
    UIImage *image;

    NSString *imageName = [event.imageName lastPathComponent];
    NSString *bundleFilePath = [[NSBundle mainBundle] pathForResource:[imageName stringByDeletingPathExtension] ofType:[imageName pathExtension]];

    image = [UIImage imageWithContentsOfFile:bundleFilePath];


    UIImageView *output = [[UIImageView alloc] initWithImage:image];
    output.frame = frame;

    UIView *descriptionView = [[UIView alloc] initWithFrame:CGRectMake(0, frame.size.height*0.7, frame.size.width, frame.size.height*0.3)];

    descriptionView.backgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:0.5];
    descriptionView.alpha = 1.0;

    UILabel *header = [[UILabel alloc] initWithFrame:CGRectMake(10, 5, frame.size.width-20, 12)];
    header.textColor = [UIColor colorWithRed:210/256.0 green:217/256.0 blue:231/256.0 alpha:1.0];
    header.font = [UIFont fontWithName:@"Helvetica" size:17];
    header.backgroundColor = [UIColor clearColor];
    header.lineBreakMode = UILineBreakModeTailTruncation;
    header.numberOfLines = 1;

    UILabel *description = [[UILabel alloc] initWithFrame:CGRectMake(10, 22, frame.size.width-20, 28)];
    description.textColor = [UIColor colorWithRed:255/256.0 green:255/256.0 blue:255/256.0 alpha:1.0];
    description.font = [UIFont fontWithName:@"Helvetica" size:12];
    description.backgroundColor = [UIColor clearColor];
    description.lineBreakMode = UILineBreakModeTailTruncation;
    description.numberOfLines = 2;

    header.text = event.title;
    [descriptionView addSubview:header];

    description.text = event.shortDesription;
    [descriptionView addSubview:description];

    [output addSubview:descriptionView];

    return output;
}

After first launch everything works fine, but if I try to reload my tableView and call addImages again, all UILabels disappear, only UIImageView and UIView are visible.

UPD:

What I have noticed, is that my UILabels appear after some time, approximately after 30 seconds. I have never experienced something similar before

UPD 2:

After I reload my tableView and scrollview , scrollView's content is not updated right away, only after I start scrolling

Answer 1

I reproduced a sample project from the code you posted, and didn't find any refreshing issues on the labels nor on any other component. This leads me to think the problem is not in the code you posted, but rather somewhere else.

Usually when you see such a delay, it is because some code that should not be running in parallel, is running in parallel.

I would suggest you check how and when you perform your call to eventsUpdated . You must make sure that call is performed on the main thread, and only once your array of events has finished updating. To check that, you can add add the following line in eventsUpdated :

NSLog(@"Current: %@, main: %@", [NSThread currentThread], [NSThread mainThread]);

Please post the log! :-)

I would suggest you also add to your question the code from the method that calls eventsUpdated , as it could also be of help.

Answer 2

At first, never do something like

 [scrollView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];

Scroll view has some internal views (scroll indicators, for example), so you're removing them which may dealloc them and cause strange crashes any time later.

As for your problem - try calling bringSubviewToFront: of your UIImageView to get your labels infront of everything else