通过变换缩放在 UIView 中不起作用

Question

在下面的程序中，无论我在 CGAffineTransform(scaleX:y:) 的参数中输入什么值，我都会得到相同的绘图结果。

这是为什么？

import UIKit

class ViewController: UIViewController {
  
  override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
    self.view.backgroundColor = .gray
  }

  override func viewWillAppear(_ animated: Bool) {
    let scalingView = ScalingView(frame: self.view.bounds)
    self.view.addSubview(scalingView)
  }
}

import UIKit

class ScalingView: UIView {
  let subview: UIView!
  
  override init(frame: CGRect) {
    subview = UIView()
    super.init(frame: frame)
    addSubview(subview)
  }
  
  required init?(coder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
  
  override func layoutSubviews() {
    subview.backgroundColor = .white
    let subviewSize = 100
    subview.frame.size = CGSize(width: subviewSize, height: subviewSize)
    subview.center = CGPoint(x: self.bounds.midX, y: self.bounds.midY)
    subview.transform = CGAffineTransform(scaleX: 1, y: 1)
  }
}

---

subview.transform = CGAffineTransform(scaleX: 1, y: 1)

---

subview.transform = CGAffineTransform(scaleX: 2, y: 2)

---

subview.transform = CGAffineTransform(scaleX: 0.5, y: 0.5)

---

https://github.com/ll3Ynxnj/Sample-Swift-ViewScaling.git

Answer 1

问题是，每次执行

subview.transform

时，

layoutSubviews

函数也会被调用，并且子视图框架也会发生变化。如果没有动画或延迟，它实际上会转换回原始帧。你可以放一些

animate

来检查：

UIView.animate(withDuration: 1) {
    self.subview.transform = CGAffineTransform(scaleX: 0.5, y: 0.5)
}

为了避免这种情况，您必须将设置大小和框架移动到

init

，这样它就会被调用一次。然后从外部改造，也许是从

ViewController

:

class ScalingView: UIView {
    override init(frame: CGRect) {
        ...
        let subviewSize = 100
        subview.frame.size = CGSize(width: subviewSize, height: subviewSize)
        subview.center = CGPoint(x: self.bounds.midX, y: self.bounds.midY)
    }

    func scaleSubView(_ scale: CGFloat = 1.5) {
        UIView.animate(withDuration: 0.3) {
            self.subview.transform = CGAffineTransform(scaleX: scale, y: scale)
        }
    }
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    scalingView.scaleSubView()
}