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");

这里有一些不同的方法:UIAnimations，在我看来，这听起来像是你的挑战。

编辑:我太懒了:)

在这篇文章中，我提到了这个方法:

[newView setFrame:CGRectMake( 0.0f, 480.0f, 320.0f, 480.0f)]; //notice this is OFF screen!
[UIView beginAnimations:@"animateTableView" context:nil];
[UIView setAnimationDuration:0.4];
[newView setFrame:CGRectMake( 0.0f, 0.0f, 320.0f, 480.0f)]; //notice this is ON screen!
[UIView commitAnimations];

但是不是动画帧，而是动画alpha:

[newView setAlpha:0.0]; // set it to zero so it is all gone.
[UIView beginAnimations:@"animateTableView" context:nil];
[UIView setAnimationDuration:0.4];
[newView setAlpha:0.5]; //this will change the newView alpha from its previous zero value to 0.5f
[UIView commitAnimations];

斯威夫特5:

当处理collectionView时。只加载一个项目或多个项目的动画。当改变单元格图像时，我尝试了一些不同的动画选项，没有区别，所以我没有在这里指明动画名称。

UIView.animate(withDuration: 1.0) { [weak self] in
                guard let self = self else { return print("gotchya!") }
                self.collectionView.reloadItems(at: [indexPath])
            }

在iOS 5中，这就简单多了:

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

为什么不试试这个呢?

NSArray *animationFrames = [NSArray arrayWithObjects:
  [UIImage imageWithName:@"image1.png"],
  [UIImage imageWithName:@"image2.png"], 
  nil];

UIImageView *animatedImageView = [[UIImageView alloc] init];
animatedImageView.animationImages = animationsFrame;
[animatedImageView setAnimationRepeatCount:1];
[animatedImageView startAnimating];

快速版本:

let animationsFrames = [UIImage(named: "image1.png"), UIImage(named: "image2.png")]
let animatedImageView = UIImageView()
animatedImageView.animationImages = animationsFrames
animatedImageView.animationRepeatCount = 1
animatedImageView.startAnimating()

Swift 5扩展:

extension UIImageView{
    func setImage(_ image: UIImage?, animated: Bool = true) {
        let duration = animated ? 0.3 : 0.0
        UIView.transition(with: self, duration: duration, options: .transitionCrossDissolve, animations: {
            self.image = image
        }, completion: nil)
    }
}