在iOS 5中，这就简单多了:

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

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

是另一种可能性

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];

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()

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)

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: