如何展开和折叠UILabel？

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var label: UILabel!
    @IBOutlet weak var expandButton: UIButton!
    
    var isExpanded = false
    let collapsedHeight: CGFloat = 50
    var expandedHeight: CGFloat = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置初始状态为折叠
        label.numberOfLines = 2
        label.lineBreakMode = .byTruncatingTail
        
        // 计算展开状态下的高度
        let labelSize = label.sizeThatFits(CGSize(width: label.frame.width, height: CGFloat.greatestFiniteMagnitude))
        expandedHeight = labelSize.height
        
        // 设置按钮点击事件
        expandButton.addTarget(self, action: #selector(expandButtonTapped), for: .touchUpInside)
    }
    
    @objc func expandButtonTapped() {
        isExpanded = !isExpanded
        
        // 更新UILabel的约束
        label.numberOfLines = isExpanded ? 0 : 2
        label.sizeToFit()
        
        // 动画地更新UILabel的约束
        UIView.animate(withDuration: 0.3) {
            self.view.layoutIfNeeded()
        }
    }
}