如何使用 Core Animation 在 iPhone 上的 2 个图像之间交叉淡入淡出

Question

我这样做是为了学习如何在 iPhone 上使用 Core Animation 动画属性（而不是学习如何交叉淡化图像本身）。

阅读关于 SO 的类似问题让我相信它可以通过像这样为 UIImageView 的 layer 的 .contents 属性设置动画来完成：

UIImage *image1 = [UIImage imageNamed:@"someImage1.png"];
UIImage *image2 = [UIImage imageNamed:@"someImage2.png"];

self.imageView.image = image1;
[self.view addSubview:self.imageView];

CABasicAnimation *crossFade = [CABasicAnimation animationWithKeyPath:@"contents"];
crossFade.duration = 5.0;
self.imageView.layer.contents = image2;
[self.imageView.layer addAnimation:crossFade forKey:@"animateContents"];

我是否弄错了细节，或者这不可能。

更新：上面的代码产生了一个空白的 UIImageView。当我更改此行时：

self.imageView.layer.contents = image2.CGImage;

...我现在可以看到图像，但它不会淡入，它只是立即出现。

Answer 1

我的建议是只使用两个UIImageViews。上图是image1，下图是image2：

- (void) crossfade {
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:.5];
    imageView1.alpha = !imageView1.alpha;
    [UIView commitAnimations];
}

无论何时调用它，它都会在两个图像之间消失。如果您只想进行一次淡入淡出并在完成后删除第一张图像：

- (void) crossfade {
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:.5];
    [UIView setAnimationDelegate:imageView1];
    [UIView setAnimationDidStopSelector:@selector(removeFromSuperview)];
    imageView1.alpha = 0
    [UIView commitAnimations];
}

编辑：

如果您正在寻找代码不起作用的原因，那是因为您只是将属性设置为新图像，然后添加了无用的动画。 CABasicAnimation 有 fromValue 和 toValue 需要设置，然后将该动画添加到图层，它应该做动画。不要手动设置内容。

Answer 2

你快到了。

CABasicAnimation *crossFade = [CABasicAnimation animationWithKeyPath:@"contents"];
crossFade.duration = 5.0;
crossFade.fromValue = image1.CGImage;
crossFade.toValue = image2.CGImage;
[self.imageView.layer addAnimation:crossFade forKey:@"animateContents"];

请注意，动画独立于 UIImageView 的实际值/内容。因此，您需要

self.imageView.image = image2;

...为您的图像设置最终结果。

Answer 3

我在某个地方找到了这个 - 效果很好。

斯威夫特

UIView.transition(with: imageView, duration: 0.33, options: .transitionCrossDissolve, animations: {
      imageView.image = image
}, completion: nil)

对象

UIImage * toImage = [UIImage imageNamed:@"image.png"];
[UIView transitionWithView:self.view
                  duration:0.33f
                   options:UIViewAnimationOptionTransitionCrossDissolve
                animations:^{
                    self.imageview.image = toImage;
                } completion:NULL];

Answer 4

extension UIImageView
{
    func mySetImage(image:UIImage)
    {
        guard let currentImage = self.image where currentImage != image else { return }
        let animation = CATransition()
        animation.duration = 0.3
        animation.type = kCATransitionFade
        layer.add(animation, forKey: "ImageFade")
        self.image = image
    }
}

Answer 5

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
self.navigationController.navigationBarHidden=false;
UIImage *img=[UIImage imageNamed:@"images.jpeg"];
imgview=[[UIImageView alloc]init];
imgview.frame=CGRectMake(30,90, img.size.width, img.size.height);
[self.view addSubview:imgview];
[self animateImages];
}
- (void)animateImages
{
static int count = 0;
NSArray *animationImages = @[[UIImage imageNamed:@"images.jpeg"], [UIImage imageNamed:@"images (1).jpeg"]];
UIImage *image = [animationImages objectAtIndex:(count % [animationImages count])];

[UIView transitionWithView:imgview
                  duration:2.0f // animation duration
                   options:UIViewAnimationOptionTransitionCrossDissolve
                animations:^{
                    imgview.image = image;
                } completion:^(BOOL finished) {
                    [self animateImages];
                    count++;
                }];

}

Answer 6

快速解决

let image1:UIImage = UIImage(named: "someImage1")!;
let image2:UIImage = UIImage(named: "someImage2")!;
let crossFade:CABasicAnimation = CABasicAnimation(keyPath: "contents");
crossFade.duration = 5.0;
crossFade.fromValue = image1.CGImage;
crossFade.toValue = image2.CGImage;
imageView.layer.addAnimation(crossFade, forKey:"animateContents");