核心动画不适用于“alpha”价值

发布于 2024-12-05 23:39:14 字数 466 浏览 7 评论 0原文

在此代码之前，我的电影图片 alpha 设置为 0，

CABasicAnimation* fadein= [CABasicAnimation animationWithKeyPath:@"alpha"];
    [fadein setToValue:[NSNumber numberWithFloat:1.0]];
    [fadein setDuration:0.5];
    [[moviepic layer]addAnimation:fadein forKey:@"alpha"];

什么也没有发生，如果我事先将 alpha 设置为 0.5，则 alpha 保持在 0.5 并且不会动画为 1。

我见过使用 UIView beginAnimations:< 的代码/code> 周围，但我正在教授核心动画，所以我想知道为什么 CABasicAnimation 不能完成这样的简单任务？

原文

Before this code, my movie pic alpha is set to 0,

CABasicAnimation* fadein= [CABasicAnimation animationWithKeyPath:@"alpha"];
    [fadein setToValue:[NSNumber numberWithFloat:1.0]];
    [fadein setDuration:0.5];
    [[moviepic layer]addAnimation:fadein forKey:@"alpha"];

Nothing happened, if I set alpha to 0.5 beforehand instead, the alpha remains at 0.5 and not animating to 1.

I've seen a code using UIView beginAnimations: around, but I'm teaching core animation so I wondered why CABasicAnimation can't do simple task like this?

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各自安好 2024-12-12 23:39:14

[CABasicAnimation animationWithKeyPath:@"opacity"];

UIView 将其公开为 alpha，而 CALayer 将其公开为 opacity。

[CABasicAnimation animationWithKeyPath:@"opacity"];

UIView exposes this as alpha where as CALayer exposes this as opacity.

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独孤求败 2024-12-12 23:39:14

对于 Swift：

let opacity = CABasicAnimation(keyPath: "opacity")
opacity.fromValue = fromValue
opacity.toValue = toValue
opacity.duration = duration
opacity.beginTime = CACurrentMediaTime() + beginTime  //If a delay is needed

view.layer.add(opacity, forKey: nil)

如果你想保留最终的 alpha 值，你必须将当前视图控制器设置为不透明度动画的委托：

opacity.delegate = self

并且，在委托函数中animationDidStop ，你应该这样做：

extension ViewController: CAAnimationDelegate {

    func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {   
        view.alpha = toValue
    }
}

For Swift:

let opacity = CABasicAnimation(keyPath: "opacity")
opacity.fromValue = fromValue
opacity.toValue = toValue
opacity.duration = duration
opacity.beginTime = CACurrentMediaTime() + beginTime  //If a delay is needed

view.layer.add(opacity, forKey: nil)

If you want to keep the final alpha value, you have to set the current view controller as the delegate of the opacity animation:

opacity.delegate = self

And, in the delegate function animationDidStop, you should do:

extension ViewController: CAAnimationDelegate {

    func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {   
        view.alpha = toValue
    }
}

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