调整UIImage大小时内存泄漏

我已经阅读了关于这个主题的多个帖子,但我的问题仍然存在。 当我使用以下代码调整图像大小时:

extension UIImage {
  func thumbnailWithMaxSize(image:UIImage, maxSize: CGFloat) -> UIImage {
    let width = image.size.width
    let height = image.size.height
    var sizeX: CGFloat = 0
    var sizeY: CGFloat = 0
    if width > height {
        sizeX = maxSize
        sizeY = maxSize * height/width
    }
    else {
        sizeY = maxSize
        sizeX = maxSize * width/height
    }

    UIGraphicsBeginImageContext(CGSize(width: sizeX, height: sizeY))
    let rect = CGRect(x: 0.0, y: 0.0, width: sizeX, height: sizeY)
    UIGraphicsBeginImageContext(rect.size)
    draw(in: rect)
    let thumbnail = UIGraphicsGetImageFromCurrentImageContext()!;

    UIGraphicsEndImageContext()

    return thumbnail

}


override func viewDidLoad() {
    super.viewDidLoad()

    let lionImage = UIImage(named: "lion.jpg")!

    var thumb = UIImage()

    autoreleasepool {
        thumb = lionImage.thumbnailWithMaxSize(image: lionImage, maxSize: 2000)
    }
    myImageView.image = thumb
}

...内存未释放。因此,当我在多个ViewController中导航时(例如,使用PageViewController),我最终会收到内存警告,应用程序最终崩溃。 有什么建议吗?