如何在Cocoa Touch中實現復雜的約束動畫

在Cocoa Touch中實現復雜的約束動畫通常涉及使用Auto Layout和Core Animation。以下是一個示例代碼，演示如何在iOS應用中使用Auto Layout和Core Animation實現復雜的約束動畫：

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var redView: UIView!
    @IBOutlet weak var blueView: UIView!
    
    var redViewCenterConstraint: NSLayoutConstraint!
    var blueViewCenterConstraint: NSLayoutConstraint!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        redViewCenterConstraint = redView.centerXAnchor.constraint(equalTo: view.centerXAnchor)
        blueViewCenterConstraint = blueView.centerXAnchor.constraint(equalTo: view.centerXAnchor)
        
        NSLayoutConstraint.activate([redViewCenterConstraint, blueViewCenterConstraint])
        
        animateViews()
    }
    
    func animateViews() {
        UIView.animate(withDuration: 1.0, animations: {
            // Update constraints
            self.redViewCenterConstraint.isActive = false
            self.redViewCenterConstraint = self.redView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: -50)
            self.redViewCenterConstraint.isActive = true
            
            self.blueViewCenterConstraint.isActive = false
            self.blueViewCenterConstraint = self.blueView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: 50)
            self.blueViewCenterConstraint.isActive = true
            
            // Trigger layout update
            self.view.layoutIfNeeded()
        }) { (_) in
            UIView.animate(withDuration: 1.0, animations: {
                // Update constraints
                self.redViewCenterConstraint.isActive = false
                self.redViewCenterConstraint = self.redView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor)
                self.redViewCenterConstraint.isActive = true
                
                self.blueViewCenterConstraint.isActive = false
                self.blueViewCenterConstraint = self.blueView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor)
                self.blueViewCenterConstraint.isActive = true
                
                // Trigger layout update
                self.view.layoutIfNeeded()
            }) { (_) in
                // Animation complete
            }
        }
    }
}

在這個示例中，我們有兩個視圖redView和blueView，它們分別位于屏幕中央。我們首先創建了兩個約束redViewCenterConstraint和blueViewCenterConstraint，并在viewDidLoad方法中激活它們。

在animateViews方法中，我們首先通過更新約束來改變視圖的位置，然后使用UIView.animate方法在1秒鐘內執行動畫。在動畫完成后，我們再次更新約束，將視圖恢復到原始位置。

這是一個簡單的示例，你可以根據自己的需求和設計來編寫更復雜的約束動畫。使用Auto Layout和Core Animation可以輕松實現各種動畫效果，并確保視圖的布局在動畫過程中保持一致和穩定。