Crash Only in iPod - ios

Question

The CRASH is:
This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.
It is clear that the problem is that every time the ui is changed must be done on the main thread. In theory this might work
dispatch_async(dispatch_get_main_queue(), {
// code here
})
My Function is:
- (void)requestInBlock:(NSString *)keyThumbnails withArrayQuantity:(NSMutableArray *)quantityArray andOriginalQuantity:(NSInteger)originalQuantity
{
int limit = 5;
NSMutableArray *arrayFive = [[NSMutableArray alloc] init];
NSInteger idQuantityOriginalCount = [quantityArray count];
for (NSInteger i = 0; i < MIN(limit, idQuantityOriginalCount); i ++) {
[arrayFive addObject:[quantityArray objectAtIndex:0]];
[quantityArray removeObjectAtIndex:0];
}
NSInteger idLimitArrayCount = [arrayFive count];
NSInteger __block countProductsRequestLimit = 0;
for (NSNumber *j in arrayFive) {
UIImageView * thumbnailImageView = [[UIImageView alloc] initWithFrame:CGRectMake(xposThumbnails, 0, ratio * 2, 47)];
[thumbnailsView addSubview:thumbnailImageView];
NSURL *imageUrl = [NSURL URLWithString:[NSString stringWithFormat:#"https://s3-us-west-2.amazonaws.com/xxxxxxxxxxxxxx/%#_%#.jpg",keyThumbnails,j]];
[Utils loadFromURL:imageUrl callback:^(UIImage *image) {
countProductsRequestLimit++;
countThumbnailsGlobal++;
[thumbnailImageView setImage:image];
[cutVideoScroll addSubview:thumbnailsView];
if (!image) {
NSMutableDictionary *collectInfoFailImage = [[NSMutableDictionary alloc] init];
[collectInfoFailImage setValue:thumbnailImageView forKey:#"image"];
[collectInfoFailImage setValue:imageUrl forKey:#"imageUrl"];
[thumbnailsWithError addObject:collectInfoFailImage];
collectInfoFailImage = nil;
}
if (countThumbnailsGlobal == originalQuantity) {
[arrayFive removeAllObjects];
[self performSelector:#selector(reloadThumbnailsWithError) withObject:nil afterDelay:3];
} else if (idLimitArrayCount == countProductsRequestLimit) {
[arrayFive removeAllObjects];
[self requestInBlock:keyThumbnails withArrayQuantity:quantityArray andOriginalQuantity:originalQuantity];
}
}];
xposThumbnails += (ratio * 2);
}
loadingTimeLine.layer.zPosition = -1;
lblloadingTimeLine.layer.zPosition = -1;
}
I think the mistake is happening here loadFromURL. (It is not sure about this, because in all devices with I do my tests, this never happens, someone outside informed me and sent me error logs)
My question is:
which part of this code may be modifying the autoLayout, maybe [cutVideoScroll addSubview:thumbnailsView];?
Why only occurs on an iPod?
UPDATE:
I'm testing with.
dispatch_async(dispatch_get_main_queue(), ^{
[thumbnailImageView setImage:image];
[cutVideoScroll addSubview:thumbnailsView];
});
But error persist.
Thanks for your time.

Answer 1

You got it right, adding subview to view trigger layoutSubviews. So you should addViews only in main thread.
Maybe you have some code specifically for iPhone / iPod in any method which you override?

Answer 2

It seems to be a combination of 2 things.
dispatch_async(dispatch_get_main_queue(), ^{
[thumbnailImageView setImage:image];
[cutVideoScroll addSubview:thumbnailsView];
});
and in all cases, he was added to thumbnailImageView the image regardless validation if (! image)