Load remote server image in UIScrollView with NSOperatoinQueue - ios

Question

I want to load some "image" (In remote server) in a UIScrollView with NSOperatoinQueue. Because If I load it with normal NSURL, NSData or with NSMutableURLRequest it takes too much time to load for all the images. After that I show those images in UIButton. Here is my code:
- (void)viewDidLoad
{
[super viewDidLoad];
[self startAnimation:nil];
self.imageDownloadingQueue = [[NSOperationQueue alloc] init];
self.imageDownloadingQueue.maxConcurrentOperationCount = 4; // many servers limit how many concurrent requests they'll accept from a device, so make sure to set this accordingly
self.imageCache = [[NSCache alloc] init];
[self performSelector:#selector(loadData) withObject:nil afterDelay:0.5];
}
-(void) loadData
{
adParser = [[AdParser alloc] loadXMLByURL:getXMLURL];
adsListArray = [adParser ads];
displayArray = [[NSMutableArray alloc] init];
for (AdInfo *adInfo1 in adsListArray)
{
AdInfo *adInfo2 = [[AdInfo alloc] init];
[adInfo2 setBannerIconURL:adInfo1.bannerIconURL];
[adInfo2 setBannerIconLink:adInfo1.bannerIconLink];
[displayArray addObject:adInfo2];
}
[self loadScrollView];
[activityIndicator stopAnimating];
}
-(void) loadScrollView
{
[self.scrollView setScrollEnabled:YES];
[self.scrollView setContentSize:CGSizeMake([displayArray count] * ScrollerWidth, ScrollerHight)];
for (int i = 0; i < [displayArray count]; i++)
{
adButtonOutLet = [[UIButton alloc] initWithFrame:CGRectMake(i*320, 0, ButtonWidth, ButtonHight)];
currentAd = [displayArray objectAtIndex:i];
NSString *imageUrlString = [currentAd bannerIconURL];
UIImage *cachedImage = [self.imageCache objectForKey:imageUrlString];
if (cachedImage)
{
[adButtonOutLet setImage:cachedImage forState:UIControlStateNormal];
}
else
{
[self.imageDownloadingQueue addOperationWithBlock:^
{
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:imageUrlString]];
UIImage *image = nil;
image = [UIImage imageWithData:imageData];
// add the image to your cache
[self.imageCache setObject:image forKey:imageUrlString];
// finally, update the user interface in the main queue
[[NSOperationQueue mainQueue] addOperationWithBlock:^
{
[adButtonOutLet setImage:image forState:UIControlStateNormal];
}];
}];
}
adButtonOutLet.userInteractionEnabled= YES;
[adButtonOutLet setTag:i];
[adButtonOutLet addTarget:self action:#selector(goToURL:) forControlEvents:UIControlEventTouchUpInside];
[self.scrollView addSubview:adButtonOutLet];
}
}
Can anyone tell me what's wrong with the above code? There is no problem of parsing or retrieving data from Remote server. I check it by NSLog. I think the NSOperationQueue have some problem, which I can't manage properly. Thanks in advance. If you needed more information, I will attach here.
Have a nice day.

Answer 1

Not sure if this is your problem or your solution, its hard to tell without testing myself.
Taken from RayWenderlich
addOperationWithBlock: if you have a simple operation that does not
need to be subclassed, you can create an operation using the block
API. If you want to reference any object from outside in the block,
remember that you should pass in a weak reference. Also, if you want
to do something that is related to the UI in the block, you must do it
on the main thread:
// Create a weak reference
__weak MyViewController *weakSelf = self;
// Add an operation as a block to a queue
[myQueue addOperationWithBlock: ^ {
NSURL *aURL = [NSURL URLWithString:#"http://www.somewhere.com/image.png"];
NSError *error = nil;
NSData *data = [NSData dataWithContentsOfURL:aURL options:nil error:&error];
UIImage *image = nil;
If (data)
image = [UIImage imageWithData:data];
// Update UI on the main thread.
[[NSOperationQueue mainQueue] addOperationWithBlock: ^ {
weakSelf.imageView.image = image;
}];
}];