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");

这太棒了

  self.imgViewPreview.transform = CGAffineTransform(scaleX: 0, y: 0)
          UIView.animate(withDuration: 1, delay: 0, usingSpringWithDamping: 0.3, initialSpringVelocity: 0, options: .curveEaseOut, animations: {
              self.imgViewPreview.image = newImage
              self.imgViewPreview.transform = .identity
          }, completion: nil)

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:

使用Swift 3

extension UIImageView{   
 var imageWithFade:UIImage?{
        get{
            return self.image
        }
        set{
            UIView.transition(with: self,
                              duration: 0.5, options: .transitionCrossDissolve, animations: {
                                self.image = newValue
            }, completion: nil)
        }
    }
}

用法:

myImageView.imageWithFade = myImage

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");

在iOS 5中，这就简单多了:

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