我是IOS开发的新手，我在UIView中有两个按钮，当用户选择纵向或横向选项时，改变UIView的大小，改变背景颜色以及我需要为这个过程添加动画。 如例:用户选择portraic，然后用户可以看到红色UIView。 点击景观选项后，动画应该开始，看起来像是，红色图像出现在前面，改变景观模式的大小（改变高度和宽度），然后转到以前的位置，将颜色改变为绿色。 我在代码上添加了小的UIView动画，它有助于您确定我们应该从哪里开始动画并完成它。 如果有人知道如何正确使用，请告诉我，并感谢您的帮助。 请参考下面的代码

import UIKit

class ViewController: UIViewController {
    
    let portraitWidth : CGFloat = 400
    let portraitHeight : CGFloat = 500
    
    let landscapeWidth : CGFloat = 700
    let landscapeHeight : CGFloat = 400
    
    var mainView: UIView!
    var mainStackView: UIStackView!
    
    let segment: UISegmentedControl = {
        let segementControl = UISegmentedControl()
        return segementControl
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.translatesAutoresizingMaskIntoConstraints = false
        
        mainStackView = UIStackView()
        mainStackView.axis = .vertical
        mainStackView.translatesAutoresizingMaskIntoConstraints = false
        mainStackView.alignment = .center
        mainStackView.distribution = .equalCentering
        self.view.addSubview(mainStackView)
        
        self.segment.insertSegment(withTitle: "Portrait", at: 0, animated: false)
        self.segment.insertSegment(withTitle: "Landscape", at: 1, animated: false)
        self.segment.selectedSegmentIndex = 0
        self.segment.addTarget(self, action: #selector(changeOrientation(_:)), for: .valueChanged)
        self.segment.translatesAutoresizingMaskIntoConstraints = false
        self.segment.selectedSegmentIndex = 0
        mainStackView.addArrangedSubview(self.segment)
        
        let safeAreaLayoutGuide = self.view.safeAreaLayoutGuide
        NSLayoutConstraint.activate([
            self.mainStackView.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 20),
            self.mainStackView.centerXAnchor.constraint(equalTo: safeAreaLayoutGuide.centerXAnchor, constant: 0),
        ])
        
        NSLayoutConstraint.activate([
            self.segment.heightAnchor.constraint(equalToConstant: 35),
            self.segment.widthAnchor.constraint(equalToConstant: 300)
        ])
        
        mainView = UIView(frame: .zero)
        mainView.translatesAutoresizingMaskIntoConstraints = false
        mainStackView.addArrangedSubview(mainView)
        mainView.backgroundColor = UIColor.red
        NSLayoutConstraint.activate([
            mainView.heightAnchor.constraint(equalToConstant: portraitHeight),
            mainView.widthAnchor.constraint(equalToConstant: portraitWidth),
            mainView.topAnchor.constraint(equalTo: segment.bottomAnchor, constant: 30)
        ])
        
    }
    
    @IBAction func changeOrientation(_ sender: UISegmentedControl) {
        self.mainView.constraints.forEach{ (constraint) in
            self.mainView.removeConstraint(constraint)
        }
        UIView.animate(withDuration: 1.0) {
            if (sender.selectedSegmentIndex == 0) {
                self.mainView.backgroundColor = UIColor.red
                NSLayoutConstraint.activate([
                    self.mainView.heightAnchor.constraint(equalToConstant: self.portraitHeight),
                    self.mainView.widthAnchor.constraint(equalToConstant: self.portraitWidth),
                    self.mainView.topAnchor.constraint(equalTo: self.segment.bottomAnchor, constant: 30)
                ])
            } else {
                self.mainView.backgroundColor = UIColor.green
                NSLayoutConstraint.activate([
                    self.mainView.heightAnchor.constraint(equalToConstant: self.landscapeHeight),
                    self.mainView.widthAnchor.constraint(equalToConstant: self.landscapeWidth),
                    self.mainView.topAnchor.constraint(equalTo: self.segment.bottomAnchor, constant: 30)
                ])
            }
        }
    }
    
    
}

更新逻辑

@IBAction func changeOrientation(_ sender: UISegmentedControl) {
    UIView.animate(withDuration: 4.0) {
        if (sender.selectedSegmentIndex == 0) {
            self.mainView.backgroundColor = UIColor.red
            self.widthConstraint.constant = self.portraitWidth
            self.heightConstraint.constant = self.portraitWidth
        } else {
            self.mainView.backgroundColor = UIColor.green
            self.widthConstraint.constant = self.landscapeWidth
            self.heightConstraint.constant = self.landscapeHeight
        }
        self.mainView.layoutIfNeeded()
    } }