Drawrect causing memory issues - iphone

Question

Currently I am using UIView instead of UIImageview due to Memory consumption in large scale images. following is same code I am using.
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
[myImage drawInRect:rect];
}
-(void) SetImage:(UIImage*) aImage
{
if(!aImage)
return;
if(myImage)
{
[myImage release];
myImage = nil;
}
myImage = [[[UIImage alloc]initWithCGImage:aImage.CGImage] retain];
[self setNeedsDisplay];
}
This is causing now memory leak of 8 MB ( checked with Instrument ) every time when Update and set the same image again. if I comment
[self setNeedsDisplay];
There is no leak. can anyone help me here if I am doing something wrong. OR can anyone help me to Subclass UIImageview to handle large scale image.
// Calling functions
-(void) FitToCardStart
{
UIImage* temp = ScaleImage([iImageBgView GetImage]);
[iImageBgView SetImage:temp];
[temp release];
temp = nil;
}
// ScaleImage
UIImage* ScaleImage(UIImage* image)
{
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
int kMaxResolution = 1800;
CGImageRef imgRef = image.CGImage;
CGFloat width = CGImageGetWidth(imgRef);
CGFloat height = CGImageGetHeight(imgRef);
CGAffineTransform transform = CGAffineTransformIdentity;
CGRect bounds = CGRectMake(0, 0, width, height);
if (width < kMaxResolution || height < kMaxResolution)
{
CGFloat ratio = width/height;
if (ratio > 1)
{
bounds.size.width = kMaxResolution;
bounds.size.height = bounds.size.width / ratio;
}
else
{
bounds.size.height = kMaxResolution;
bounds.size.width = bounds.size.height * ratio;
}
}
CGFloat scaleRatio = bounds.size.width / width;
CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
UIImageOrientation orient = image.imageOrientation;
switch(orient)
{
case UIImageOrientationUp: //default
transform = CGAffineTransformIdentity;
break;
default:
[NSException raise:NSInternalInconsistencyException format:#"Invalid image orientation"];
}
UIGraphicsBeginImageContext(bounds.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextScaleCTM(context, scaleRatio, -scaleRatio);
CGContextTranslateCTM(context, 0, -height);
CGContextConcatCTM(context, transform);
CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
UIImage* temp = [[[UIImage alloc] initWithCGImage:imageCopy.CGImage] retain];
CGImageRelease(imgRef);
CGContextRelease(context);
[pool release];
return temp;
}
Thanks,
Sagar

Answer 1

Your problem is this line:
myImage = [[[UIImage alloc]initWithCGImage:aImage.CGImage] retain];
alloc already gives you a retain count of 1, with the additional retain you end up with a retain count of 2 which is too high. Remove the retain and everything will be fine.

Answer 2

myImage = [[[UIImage alloc]initWithCGImage:aImage.CGImage] retain];
There's redundant retain in this line - as you're allocating new UIIMage object (use +alloc) method you don't need to extra retain it.
Edit: ScaleImage method has the same problem with redundant retain:
// remove extra retain here
UIImage* temp = [[[UIImage alloc] initWithCGImage:imageCopy.CGImage] retain];
// should be
UIImage* temp = [[UIImage alloc] initWithCGImage:imageCopy.CGImage];
And a code-style comment - it is better to indicate in your method names what memory management behavior required for returned objects - as image returned by your method needs to be released method name should contain something from "new", "alloc", "copy", "create"...

Answer 3

I suggest not creating a new image, but just keeping the aImage instance.
myImage = [aImage retain];
I you absolutely must make it a new instance, you are doing it in a very roundabout way.
Copying would be a much better alternative.
myImage = [aImage copy];