我不确定你是否可以用渐隐效果动画UIViews，因为似乎所有支持的视图转换都在UIViewAnimationTransition枚举中定义。渐变效果可以使用CoreAnimation实现。该方法的示例示例:

#import <QuartzCore/QuartzCore.h>
...
imageView.image = [UIImage imageNamed:(i % 2) ? @"3.jpg" : @"4.jpg"];

CATransition *transition = [CATransition animation];
transition.duration = 1.0f;
transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
transition.type = kCATransitionFade;

[imageView.layer addAnimation:transition forKey:nil];

CABasicAnimation* fadeAnim = [CABasicAnimation animationWithKeyPath:@"contents"];
fadeAnim.fromValue = (__bridge id)imageView.image.CGImage;
fadeAnim.toValue = (__bridge id)[UIImage imageNamed:@"newImage.png"].CGImage;
fadeAnim.duration = 2.0;
[imageView.layer addAnimation:fadeAnim forKey:@"contents"];
imageView.layer.contents = (__bridge id)[UIImage imageNamed:@"newImage.png"].CGImage;

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()

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

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
    }

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])
            }