UIGraphicsBeginImageContext created image stays in memory forever

问题

I'm creating many colour variations of an image using Core Graphics. I need to create about 320 in total but gradually, the memory usage of the app keeps increasing until it crashes. From Instruments, I see that more CGImage objects are being created and stay alive. I want to release them because I store the images to the cache directory in PNG format.

I have searched through all other solutions I could find without success. Any help is appreciated. Thanks.

Here's the main part:

+(UIImage *)tintedImageFromImage:(UIImage *)sourceImage colour:(UIColor *)color intensity:(float)intensity {

    if (UIGraphicsBeginImageContextWithOptions != NULL) {

        UIGraphicsBeginImageContextWithOptions(sourceImage.size, NO, 0.0);

    } else {

        UIGraphicsBeginImageContext(sourceImage.size);
    }

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGRect rect = CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height);

    // draw alpha-mask
    CGContextSetBlendMode(context, kCGBlendModeNormal);
    CGContextDrawImage(context, rect, sourceImage.CGImage);

    // draw tint color, preserving alpha values of original image
    CGContextSetBlendMode(context, kCGBlendModeSourceIn);
    [color setFill];
    CGContextFillRect(context, rect);


    //Set the original greyscale template as the overlay of the new image
    sourceImage = [self verticallyFlipImage:sourceImage];
    [sourceImage drawInRect:CGRectMake(0,0, sourceImage.size.width,sourceImage.size.height) blendMode:kCGBlendModeMultiply alpha:intensity];

    UIImage *colouredImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    colouredImage = [self verticallyFlipImage:colouredImage];


    return colouredImage;
}

this is used to flip the image:

+(UIImage *)verticallyFlipImage:(UIImage *)originalImage {

    UIImageView *tempImageView = [[UIImageView alloc] initWithImage:originalImage];

    UIGraphicsBeginImageContext(tempImageView.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, tempImageView.frame.size.height);

    CGContextConcatCTM(context, flipVertical);

    [tempImageView.layer renderInContext:context];

    UIImage *flippedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return flippedImage;
}

回答1:

Add to verticallyFlipImage the line tempImageView.image = nil; in order to make the image view release the image. This solves the problem.

来源：https://stackoverflow.com/questions/17263533/uigraphicsbeginimagecontext-created-image-stays-in-memory-forever

标签

memory-leaks

uiimage

core-graphics

cgcontext

cgimage