Objective C Memory Crash, UIImageView - objective-c

Question

My app assigns and displays an image inside of a UIImageView. This happens with 24 imageViews all at viewDidLoad. The images are assigned randomly from a list of fifty images. The view controller is pushed to modally from the main screen. The first time it takes a while to load. If I'm lucky, the view loads a second time. The third time, it almost always crashes. I've tried resizing the images to around 200 pixels. I've tried assigning the images with :
image1 = [UIImage imageNamed:#"image1.png"];
[self.imageView setImage: image1];
and also with:
NSString *imagePath = [[NSBundle mainBundle] pathForResource:#"image1" ofType:#"png"];
image1 = [[UIImage alloc] initWithContentsOfFile:imagePath];
This second one seemed to only make things worse.
I also tried running the app with Instruments, which didn't recognize any memory leaks.
I really don't know where else to turn. This app represents an enormous investment of time and I would really like to see this problem resolved...
Thank you so much

Answer 1

The most efficient way to load a smaller version of an image from disk is this: instead of using imageNamed:, use the Image I/O framework to request a thumbnail that is the actual size you'll be displaying, by calling CGImageSourceCreateThumbnailAtIndex. Here's the example from my book:
NSURL* url =
[[NSBundle mainBundle] URLForResource:#"colson"
withExtension:#"jpg"];
CGImageSourceRef src =
CGImageSourceCreateWithURL((__bridge CFURLRef)url, nil);
CGFloat scale = [UIScreen mainScreen].scale;
CGFloat w = self.iv.bounds.size.width*scale;
NSDictionary* d =
#{(id)kCGImageSourceShouldAllowFloat: (id)kCFBooleanTrue,
(id)kCGImageSourceCreateThumbnailWithTransform: (id)kCFBooleanTrue,
(id)kCGImageSourceCreateThumbnailFromImageAlways: (id)kCFBooleanTrue,
(id)kCGImageSourceThumbnailMaxPixelSize: #((int)w)};
CGImageRef imref =
CGImageSourceCreateThumbnailAtIndex(src, 0, (__bridge CFDictionaryRef)d);
UIImage* im =
[UIImage imageWithCGImage:imref scale:scale
orientation:UIImageOrientationUp];
self.iv.image = im;
CFRelease(imref); CFRelease(src);
It is a huge waste of memory to ask a UIImageView to display an image larger than the UIImageView itself, as the bitmap for the full-size image must be maintained in memory. The Image I/O framework generates the smaller version without even ever unpacking the entire original image into memory as a bitmap.

Answer 2

I had this problem once before with images from a regular website that were way larger than the view I was using. The images are being uncompressed to their full resolution and then fit into the image view, if I remember correctly, hogging up your memory. I had to scale them down to the image view size first before showing them. Add CoreGraphics.framework and use this class to make an image object to use with your image view. I found it online and tweaked it a little looking for the same answer but don't remember where, so thanks to that person who posted the original, whoever they are.
ImageScale.h
#import <Foundation/Foundation.h>
#interface ImageScale : NSObject
+ (UIImage*)imageWithImage:(UIImage*)sourceImage scaledToSize:(CGSize)newSize;
#end
ImageScale.m
#import "ImageScale.h"
#implementation ImageScale
+ (UIImage*)imageWithImage:(UIImage*)sourceImage scaledToSize:(CGSize)newSize
{
CGFloat targetWidth = newSize.width;
CGFloat targetHeight = newSize.height;
CGImageRef imageRef = [sourceImage CGImage];
CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
if (bitmapInfo == kCGImageAlphaNone) {
bitmapInfo = kCGImageAlphaNoneSkipLast;
}
CGContextRef bitmap;
if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
} else {
bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
}
if (sourceImage.imageOrientation == UIImageOrientationLeft) {
CGContextRotateCTM (bitmap, M_PI_2); // + 90 degrees
CGContextTranslateCTM (bitmap, 0, -targetHeight);
} else if (sourceImage.imageOrientation == UIImageOrientationRight) {
CGContextRotateCTM (bitmap, -M_PI_2); // - 90 degrees
CGContextTranslateCTM (bitmap, -targetWidth, 0);
} else if (sourceImage.imageOrientation == UIImageOrientationUp) {
// NOTHING
} else if (sourceImage.imageOrientation == UIImageOrientationDown) {
CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
CGContextRotateCTM (bitmap, -M_PI); // - 180 degrees
}
CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage* newImage = [UIImage imageWithCGImage:ref];
CGContextRelease(bitmap);
CGImageRelease(ref);
return newImage;
}
#end