CGAffineTransform：同时应用平移和缩放

Question

我有两个UILabels。屏幕左侧较大，右侧较小。

我正在尝试使用CGAffineTransform 将较小的标签移动到较大标签的位置并将其缩放到相同大小，然后将较大的标签移出屏幕。

我实际上并没有移动标签，动画完成后，我更改了标签上的文本属性并将它们的变换设置为identity。

我的问题是我不知道如何计算必须转换较小标签的确切 x 和 y 值。我认为我的值不准确，因为我在翻译标签的同时缩放标签，tx 和 ty 值是使用较小标签的未缩放大小计算的。

我目前在做什么： tx：大标签的宽度+与小标签的距离，ty：y轴上两个标签中心的距离

Answer 1

有多种方法可以做到这一点 - 这里有一个......

首先计算平移值和比例值，然后将它们连接起来：

    let translation = CGAffineTransform(translationX: xMove, y: yMove)
    let scaling = CGAffineTransform(scaleX: xScale, y: yScale)
    
    let fullTransform = scaling.concatenating(translation)
    

这是一个完整的示例...我们添加了两个具有不同字体大小、位置和背景颜色的标签（以便于查看）。点击任意位置运行变换动画：

class ViewController: UIViewController {

    let labelA = UILabel()
    let labelB = UILabel()
    
    var aTop: NSLayoutConstraint!
    var aLeading: NSLayoutConstraint!

    var bTop: NSLayoutConstraint!
    var bLeading: NSLayoutConstraint!
    
    override func viewDidLoad() {
        super.viewDidLoad()

        [labelA, labelB].forEach { v in
            v.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(v)
        }
        
        labelA.text = "Label A"
        labelB.text = "Label B"
        
        labelA.backgroundColor = .green
        labelB.backgroundColor = .cyan
        
        labelA.font = .systemFont(ofSize: 40.0)
        labelB.font = .systemFont(ofSize: 20.0)

        // respect safe area
        let g = view.safeAreaLayoutGuide
        
        aTop = labelA.topAnchor.constraint(equalTo: g.topAnchor, constant: 100.0)
        aLeading = labelA.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0)
        
        bTop = labelB.topAnchor.constraint(equalTo: g.topAnchor, constant: 300.0)
        bLeading = labelB.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 240.0)
        
        NSLayoutConstraint.activate([
            aTop, aLeading,
            bTop, bLeading,
        ])
        
        let t = UITapGestureRecognizer(target: self, action: #selector(self.doAnim(_:)))
        view.addGestureRecognizer(t)
        
    }
    
    @objc func doAnim(_ g: UITapGestureRecognizer?) -> Void {
        
        let targetPoint = labelA.center
        let originPoint = labelB.center
        
        let xMove = targetPoint.x - originPoint.x
        let yMove = targetPoint.y - originPoint.y

        let xScale = labelA.frame.width / labelB.frame.width
        let yScale = labelA.frame.height / labelB.frame.height
        
        let translation = CGAffineTransform(translationX: xMove, y: yMove)
        let scaling = CGAffineTransform(scaleX: xScale, y: yScale)
        
        let fullTransform = scaling.concatenating(translation)
        
        UIView.animate(withDuration: 1.0, animations: {
            self.labelB.transform = fullTransform
        }) { [weak self] b in
            guard let self = self else { return }
            self.labelB.transform = .identity
            self.labelB.font = self.labelA.font
            self.bTop.constant = self.aTop.constant
            self.bLeading.constant = self.aLeading.constant
        }

    }
    
}