Background
I have searched around SO and apple forum. Quite a lot of people talked about performance of collection view cell with image. Most of them said it is lag on scroll since loading the image in the main thread.
By using SDWebImage, the images should be loading in separate thread. However, it is lag only in the landscape mode in the iPad simulator.
Problem description
In the portrait mode, the collection view load 3 cells for each row. And it has no lag or insignificant delay. In the landscape mode, the collection view load 4 cells for each row. And it has obvious lag and drop in frame rate.
I have checked with instrument tools with the core animation. The frame rate drop to about 8fps when new cell appear. I am not sure which act bring me such a low performance for the collection view.
Hope there would be someone know the tricks part.
Here are the relate code
In The View Controller
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
ProductCollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"ProductViewCell" forIndexPath:indexPath];
Product *tmpProduct = (Product*)_ploader.loadedProduct[indexPath.row];
cell.product = tmpProduct;
if (cellShouldAnimate) {
cell.alpha = 0.0;
[UIView animateWithDuration:0.2
delay:0
options:(UIViewAnimationOptionCurveLinear | UIViewAnimationOptionAllowUserInteraction)
animations:^{
cell.alpha = 1.0;
} completion:nil];
}
if(indexPath.row >= _ploader.loadedProduct.count - ceil((LIMIT_COUNT * 0.3)))
{
[_ploader loadProductsWithCompleteBlock:^(NSError *error){
if (nil == error) {
cellShouldAnimate = NO;
[_collectionView reloadData];
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
cellShouldAnimate = YES;
});
} else if (error.code != 1){
#ifdef DEBUG_MODE
ULog(@"Error.des : %@", error.description);
#else
CustomAlertView *alertView = [[CustomAlertView alloc]
initWithTitle:@"Connection Error"
message:@"Please retry."
buttonTitles:@[@"OK"]];
[alertView show];
#endif
}
}];
}
return cell;
}
PrepareForReuse in the collectionViewCell
- (void)prepareForReuse
{
[super prepareForReuse];
CGRect bounds = self.bounds;
[_thumbnailImgView sd_cancelCurrentImageLoad];
CGFloat labelsTotalHeight = bounds.size.height - _thumbnailImgView.frame.size.height;
CGFloat brandToImageOffset = 2.0;
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
brandToImageOffset = 53.0;
}
CGFloat labelStartY = _thumbnailImgView.frame.size.height + _thumbnailImgView.frame.origin.y + brandToImageOffset;
CGFloat nameLblHeight = labelsTotalHeight * 0.46;
CGFloat priceLblHeight = labelsTotalHeight * 0.18;
_brandLbl.frame = (CGRect){{15, labelStartY}, {bounds.size.width - 30, nameLblHeight}};
CGFloat priceToNameOffset = 8.0;
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
priceToNameOffset = 18.0;
}
_priceLbl.frame = (CGRect){{5, labelStartY + nameLblHeight - priceToNameOffset}, {bounds.size.width-10, priceLblHeight}};
[_spinner stopAnimating];
[_spinner removeFromSuperview];
_spinner = nil;
}
Override the setProduct method
- (void)setProduct:(Product *)product
{
_product = product;
_spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
_spinner.center = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
[self addSubview:_spinner];
[_spinner startAnimating];
_spinner.hidesWhenStopped = YES;
// Add a spinner
__block UIActivityIndicatorView *tmpSpinner = _spinner;
__block UIImageView *tmpImgView = _thumbnailImgView;
ProductImage *thumbnailImage = _product.images[0];
[_thumbnailImgView sd_setImageWithURL:[NSURL URLWithString:thumbnailImage.mediumURL]
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
// dismiss the spinner
[tmpSpinner stopAnimating];
[tmpSpinner removeFromSuperview];
tmpSpinner = nil;
if (nil == error) {
// Resize the incoming images
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
CGFloat imageHeight = image.size.height;
CGFloat imageWidth = image.size.width;
CGSize newSize = tmpImgView.bounds.size;
CGFloat scaleFactor = newSize.width / imageWidth;
newSize.height = imageHeight * scaleFactor;
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *small = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
dispatch_async(dispatch_get_main_queue(),^{
tmpImgView.image = small;
});
});
if (cacheType == SDImageCacheTypeNone) {
tmpImgView.alpha = 0.0;
[UIView animateWithDuration:0.2
delay:0
options:(UIViewAnimationOptionCurveLinear | UIViewAnimationOptionAllowUserInteraction)
animations:^{
tmpImgView.alpha = 1.0;
} completion:nil];
}
} else {
// loading error
[tmpImgView setImage:[UIImage imageNamed:@"broken_image_small"]];
}
}];
_brandLbl.text = [_product.brand.name uppercaseString];
_nameLbl.text = _product.name;
[_nameLbl sizeToFit];
// Format the price
NSNumberFormatter * floatFormatter = [[NSNumberFormatter alloc] init];
[floatFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
[floatFormatter setDecimalSeparator:@"."];
[floatFormatter setMaximumFractionDigits:2];
[floatFormatter setMinimumFractionDigits:0];
[floatFormatter setGroupingSeparator:@","];
_priceLbl.text = [NSString stringWithFormat:@"$%@ USD", [floatFormatter stringFromNumber:_product.price]];
if (_product.salePrice.intValue > 0) {
NSString *rawStr = [NSString stringWithFormat:@"$%@ $%@ USD", [floatFormatter stringFromNumber:_product.price], [floatFormatter stringFromNumber:_product.salePrice]];
NSMutableAttributedString * string = [[NSMutableAttributedString alloc] initWithString:rawStr];
// Change all the text to red first
[string addAttribute:NSForegroundColorAttributeName
value:[UIColor colorWithRed:157/255.0 green:38/255.0 blue:29/255.0 alpha:1.0]
range:NSMakeRange(0,rawStr.length)];
// find the first space
NSRange firstSpace = [rawStr rangeOfString:@" "];
// Change from zero to space to gray color
[string addAttribute:NSForegroundColorAttributeName
value:_priceLbl.textColor
range:NSMakeRange(0, firstSpace.location)];
[string addAttribute:NSStrikethroughStyleAttributeName
value:@2
range:NSMakeRange(0, firstSpace.location)];
_priceLbl.attributedText = string;
}
}
