Image in UITableView using too much memory - objective-c

Question

I created a class for download images from URLs for UITableViewCells (in this project I cannot use SDWebImageView or other codes from internet) but it looks like it's using a lot of memory and my tableview is not loading so fast. Can anybody point what is the problem?
Code:
//MyHelper class
+(NSString *)pathForImage:(NSString *)urlImageString{
if ([urlImageString class] == [NSNull class] || [urlImageString isEqualToString:#"<null>"] || [urlImageString isEqualToString:#""]) {
return #"";
}
NSArray *pathsInString = [urlImageString componentsSeparatedByString:#"/"];
NSString *eventCodeString = [pathsInString objectAtIndex:[pathsInString count] - 2];
NSString *imageNameString = [pathsInString lastObject];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *cachePath = [paths objectAtIndex:0];
cachePath = [MyHelper validateString:[cachePath stringByAppendingString:eventCodeString]];
[cachePath stringByAppendingString:#"/"];
return [cachePath stringByAppendingString:imageNameString];
}
+(BOOL)imageExistsForURL:(NSString *)urlString{
if (!([urlString class] == [NSNull class]))
{
NSString *filePath = [MyHelper pathForImage:urlString];
NSFileManager *fileManager = [NSFileManager defaultManager];
return [fileManager fileExistsAtPath:filePath];
}
return false;
}
+(void)setAsyncImage:(UIImageView *)imageView forDownloadImage:(NSString *)urlString{
CGRect activityFrame = CGRectMake(0, 0, 60, 60);
UIActivityIndicatorView *activity = [[UIActivityIndicatorView alloc] initWithFrame:activityFrame];
activity.layer.cornerRadius = activity.frame.size.width / 2;
activity.clipsToBounds = YES;
activity.activityIndicatorViewStyle = UIActivityIndicatorViewStyleGray;
[imageView addSubview:activity];
[activity startAnimating];
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(concurrentQueue, ^{
NSData *image;
if ([urlString class] == [NSNull class]) {
image = nil;
} else {
image = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:urlString]];
}
dispatch_async(dispatch_get_main_queue(), ^{
[activity stopAnimating];
[activity removeFromSuperview];
if (image)
{
[UIView animateWithDuration:0.9 animations:^{
imageView.alpha = 0;
imageView.image = [UIImage imageWithData:image];
imageView.alpha = 1;
}];
NSString *filePath = [MyHelper pathForImage:urlString];
NSError *error;
[image writeToFile:filePath options:NSDataWritingAtomic error:&error];
}
else
{
imageView.image = [UIImage imageNamed:#"icn_male.png"];
}
});
});
}
+(NSString *)validateString:(NSString *)string{
if (string == (id)[NSNull null] || string.length == 0 )
return #"";
return string;
}
+ (UIImage*)imageWithImage:(UIImage*)image
scaledToSize:(CGSize)newSize;
{
float proportion;
if (image.size.height > image.size.width) {
proportion = image.size.height / newSize.height;
} else {
proportion = image.size.width / newSize.width;
}
UIGraphicsBeginImageContext( newSize );
[image drawInRect:CGRectMake(newSize.width - (image.size.width/proportion),
newSize.height/2 - (image.size.height/proportion)/2,
image.size.width/proportion,
image.size.height/proportion)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
Using this code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSString *cellIdentifier = #"MyCell";
MyCell *cell = (MyCell *)[tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];
if ([MyHelper imageExistsForURL:photoURLString ]) {
UIImage *image = [UIImage imageWithContentsOfFile:[MyHelper pathForImage:photoURLString]];
eventImageView.image = [MyHelper imageWithImage:image scaledToSize:CGSizeMake(60, 60)];
} else {
[MyHelper setAsyncImage:eventImageView forDownloadImage:photoURLString ];
}
}

Answer 1

Since it is now clear that you are using oversized images, the solution is to figure out how big your images need to be in order to look good in your app.
There are several courses of action depending on how much you can change the server side portion of your system.
Use an image that is optimally sized for the highest-res case (3x) and let 2x and 1x devices do the scaling. This is again a bit wasteful.
Create some scheme whereby you will be able to get the right size image for your device type (perhaps by appending 2x, 3x etc.) to the image file name. Arguably the best choice.
Do the resizing on the client side. This can be somewhat CPU intensive and is probably the worst approach in my opinion because you will be doing a lot of work unnecessarily. However, if you can't change how your server works, then this is your only option.
Another problem with your code is that you are doing the resizing on the main/UI thread, which is blocking your UI, which is a no-no. Never perform long operations on the main thread.
You should be doing it on a background thread using dispatch_async or perhaps NSOperation and a sequential queue to reduce memory usage. Note that this can create new problems because you have to update your image view when the image is ready and consider things such as whether the cell is still visible or not. I came across a nice blog post on this a while back so I suggest searching the web.
However, if the images are really huge, then maybe you could consider setting up a proxy server and then getting resized images from there instead of the main server. Of course, you would have to consider intellectual property issues in this case.