Swift：核心动画没有动画效果

Question

当谈到Core Animation时，我是一个noobie。我试图实现简单的动画，其中UILabel从A点移动到B点。我从动画代码示例中获得以下代码，但无法使其工作。标签根本不会移动。我究竟做错了什么？

let frame = self.view.frame 
let blueBox = UIView(frame: frame) 
blueBox.backgroundColor = UIColor(red: 46/255, green: 83/255, blue: 160/255, alpha: 1.0) 

let label = UILabel(frame: CGRect(x: 0, y: 0, width: 300, height: 400)) 
label.center = CGPoint(x: frame.size.width/2, y: frame.size.height/2) 
label.textAlignment = .center 
label.lineBreakMode = .byWordWrapping 
label.numberOfLines = 0 

label.layer.position = label.center 

var attrsA = [NSFontAttributeName: UIFont(name: "LemonMilk", size: 92), NSForegroundColorAttributeName: UIColor.white] 
var a = NSMutableAttributedString(string:"Hello\n", attributes:attrsA) 
var attrsB = [NSFontAttributeName: UIFont(name: "LemonMilk", size: 38), NSForegroundColorAttributeName: UIColor.white] 
var b = NSAttributedString(string:"World", attributes:attrsB) 
a.append(b) 


label.attributedText = a 

let theAnimation = CABasicAnimation(keyPath: "position"); 
theAnimation.fromValue = [NSValue(cgPoint: CGPoint(x: screenWidth/2, y: screenHeight/2))] 
theAnimation.toValue = [NSValue(cgPoint: CGPoint(x: 100.0, y: 100.0))] 
theAnimation.duration = 3.0; 
theAnimation.autoreverses = false //true - reverses into the initial value either smoothly or not 
theAnimation.repeatCount = 2 

blueBox.addSubview(label) 

view.addSubview(blueBox) 
label.layer.add(theAnimation, forKey: "animatePosition"); 

Answer 1

首先：你不能在label和add(animation:)上label.layer相提并论调用addSubview。您只能在视图层次结构中为已经设置视图。换句话说，即使你的代码的一切都很好，你也打电话给add(animation:)太快。尝试引入delay。

二：这些线是虚假：

theAnimation.fromValue = [NSValue(cgPoint: CGPoint(x: screenWidth/2, y: screenHeight/2))] 
theAnimation.toValue = [NSValue(cgPoint: CGPoint(x: 100.0, y: 100.0))] 

既不fromValue也不toValue可以是阵列。摆脱这些大括号。而在Swift 3.0.1和更高版本中，你不需要胁迫NSValue。所以：

theAnimation.fromValue = CGPoint(x: screenWidth/2, y: screenHeight/2) 
theAnimation.toValue = CGPoint(x: 100.0, y: 100.0) 

三：什么是fromValue甚至？如果您想从标签已有的位置开始动画，只需省略fromValue即可。

因此，我修改了代码，就这样结束了，我看到了动画：

label.attributedText = a 
blueBox.addSubview(label) 
view.addSubview(blueBox) 
delay(1) { 
    let theAnimation = CABasicAnimation(keyPath: "position"); 
    theAnimation.toValue = CGPoint(x: 100.0, y: 100.0) 
    theAnimation.duration = 3.0; 
    theAnimation.autoreverses = false //true - reverses into the initial value either smoothly or not 
    theAnimation.repeatCount = 2 
    label.layer.add(theAnimation, forKey: "animatePosition"); 
}