Specifies whether image decoding and caching should happen at image creation time.

在Objc.io #7彼得·斯坦伯格(Peter Steinberger)建议这样做：

+ (UIImage *)decompressedImageWithData:(NSData *)data 
{
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)data,NULL);
    CGImageRef cgImage = CGImageSourceCreateImageAtIndex(source,(__bridge CFDictionaryRef)@{(id)kCGImageSourceShouldCacheImmediately: @YES});

    UIImage *image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    CFRelease(source);
    return image;
}

像AFNetworking和SDWebImage这样的库仍然使用CGContextDrawImage方法进行图像解压缩.从SDWebImage：

+ (UIImage *)decodedImageWithImage:(UIImage *)image {
    if (image.images) {
        // Do not decode animated images
        return image;
    }

    CGImageRef imageRef = image.CGImage;
    CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef),CGImageGetHeight(imageRef));
    CGRect imageRect = (CGRect){.origin = CGPointZero,.size = imageSize};

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

    int infoMask = (bitmapInfo & kCGBitmapAlphaInfoMask);
    BOOL anyNonAlpha = (infoMask == kCGImageAlphaNone ||
            infoMask == kCGImageAlphaNoneSkipFirst ||
            infoMask == kCGImageAlphaNoneSkipLast);

    // CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.
    // https://developer.apple.com/library/mac/#qa/qa1037/_index.html
    if (infoMask == kCGImageAlphaNone && CGColorSpaceGetNumberOfComponents(colorSpace) > 1) {
        // Unset the old alpha info.
        bitmapInfo &= ~kCGBitmapAlphaInfoMask;

        // Set noneSkipFirst.
        bitmapInfo |= kCGImageAlphaNoneSkipFirst;
    }
            // Some PNGs tell us they have alpha but only 3 components. Odd.
    else if (!anyNonAlpha && CGColorSpaceGetNumberOfComponents(colorSpace) == 3) {
        // Unset the old alpha info.
        bitmapInfo &= ~kCGBitmapAlphaInfoMask;
        bitmapInfo |= kCGImageAlphaPremultipliedFirst;
    }

    // It calculates the bytes-per-row based on the bitsPerComponent and width arguments.
    CGContextRef context = CGBitmapContextCreate(NULL,imageSize.width,imageSize.height,CGImageGetBitsPerComponent(imageRef),colorSpace,bitmapInfo);
    CGColorSpaceRelease(colorSpace);

    // If Failed,return undecompressed image
    if (!context) return image;

    CGContextDrawImage(context,imageRect,imageRef);
    CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);

    CGContextRelease(context);

    UIImage *decompressedImage = [UIImage imageWithCGImage:decompressedImageRef scale:image.scale orientation:image.imageOrientation];
    CGImageRelease(decompressedImageRef);
    return decompressedImage;
}

我的问题是我们应该在iOS 7中移动到kCGImageSourceShouldCacheImmediately方法吗？