代码:

var fadeAnim:CABasicAnimation = CABasicAnimation(keyPath: "contents");

fadeAnim.fromValue = firstImage;
fadeAnim.toValue   = secondImage;
fadeAnim.duration  = 0.8;         //smoothest value

imageView.layer.addAnimation(fadeAnim, forKey: "contents");

imageView.image = secondImage;

例子:

有趣，更详细的解决方案:(切换水龙头)

    let fadeAnim:CABasicAnimation = CABasicAnimation(keyPath: "contents");

    switch imageView.image {
        case firstImage?:
            fadeAnim.fromValue = firstImage;
            fadeAnim.toValue   = secondImage;
            imageView.image    = secondImage;
        default:
            fadeAnim.fromValue = secondImage;
            fadeAnim.toValue   = firstImage;
            imageView.image    = firstImage;
    }

    fadeAnim.duration = 0.8;

    imageView.layer.addAnimation(fadeAnim, forKey: "contents");

下面是Swift中的一个例子，它将首先交叉溶解一个新图像，然后添加一个弹性动画:

var selected: Bool {
  willSet(selected) {
    let expandTransform:CGAffineTransform = CGAffineTransformMakeScale(1.15, 1.15);
    if (!self.selected && selected) {
      UIView.transitionWithView(self.imageView,
        duration:0.1,
        options: UIViewAnimationOptions.TransitionCrossDissolve,
        animations: {
          self.imageView.image = SNStockCellSelectionAccessoryViewImage(selected)
          self.imageView.transform = expandTransform
        },
        completion: {(finished: Bool) in
          UIView.animateWithDuration(0.4,
            delay:0.0,
            usingSpringWithDamping:0.40,
            initialSpringVelocity:0.2,
            options:UIViewAnimationOptions.CurveEaseOut,
            animations: {
              self.imageView.transform = CGAffineTransformInvert(expandTransform)
            }, completion:nil)
      })
    }
  }
}

var imageView:UIImageView

如果imageView被正确地作为子视图添加到视图中，在selected = false到selected = true之间切换应该用一个弹性动画交换图像。SNStockCellSelectionAccessoryViewImage只是根据当前的选择状态返回一个不同的图像，如下所示:

private let SNStockCellSelectionAccessoryViewPlusIconSelected:UIImage = UIImage(named:"PlusIconSelected")!
private let SNStockCellSelectionAccessoryViewPlusIcon:UIImage = UIImage(named:"PlusIcon")!

private func SNStockCellSelectionAccessoryViewImage(selected:Bool) -> UIImage {
  return selected ? SNStockCellSelectionAccessoryViewPlusIconSelected : SNStockCellSelectionAccessoryViewPlusIcon
}

下面的GIF例子有点慢，实际的动画发生得更快:

[UIView transitionWithView:textFieldimageView
                  duration:0.2f
                   options:UIViewAnimationOptionTransitionCrossDissolve
                animations:^{
                    imageView.image = newImage;
                } completion:nil];

是另一种可能性

在iOS 5中，这就简单多了:

[newView setAlpha:0.0];
[UIView animateWithDuration:0.4 animations:^{
    [newView setAlpha:0.5];
}];

用迈克尔·斯科特的话来说，傻瓜，保持简单。 以下是在Swift 3和Swift 4中实现这一点的简单方法:

UIView.transition(with: imageView,
                  duration: 0.75,
                  options: .transitionCrossDissolve,
                  animations: { self.imageView.image = toImage },
                  completion: nil)

弗拉基米尔的答案是完美的，但任何像我这样正在寻找快速解决方案的人

该方案适用于swift 4.2版本

var i = 0
    func animation(){
        let name = (i % 2 == 0) ? "1.png" : "2.png"
        myImageView.image = UIImage.init(named: name)
        let transition: CATransition = CATransition.init()
        transition.duration = 1.0
        transition.timingFunction = CAMediaTimingFunction.init(name: .easeInEaseOut)
        transition.type = .fade
        myImageView.layer.add(transition, forKey: nil)
        i += 1
    }

您可以在任何地方调用此方法。它将改变图像到下一个(图像)与动画。

对于Swift 4.0版本使用波纹管解决方案

var i = 0
    func animationVersion4(){
        let name = (i % 2 == 0) ? "1.png" : "2.png"
        uiImage.image = UIImage.init(named: name)
        let transition: CATransition = CATransition.init()
        transition.duration = 1.0
        transition.timingFunction = CAMediaTimingFunction.init(name: kCAMediaTimingFunctionEaseInEaseOut)
        transition.type = kCATransitionFade
        uiImage.layer.add(transition, forKey: nil)
        i += 1
    }