如何在UIView中展示启动动画？OnboardingController动画失效求助

问题根源 #

你将动画逻辑放在了Page类的init(frame:)方法中，此时视图尚未完成布局（Auto Layout约束还未计算出最终的frame），视图也还未被添加到视图层级并渲染到屏幕上，导致动画无法被系统正确触发。

解决方案一：在layoutSubviews中执行动画 #

layoutSubviews会在视图完成布局后被调用，是执行布局相关动画的合适时机。同时添加标记避免动画重复触发：

class Page: UIView {
    private let imageView: UIImageView = {
        let image = UIImageView()
        image.image = UIImage(named: "1")
        image.translatesAutoresizingMaskIntoConstraints = false
        return image
    }()
    
    // 标记动画是否已执行，防止重复触发
    private var animationPlayed = false
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(imageView)
        
        // 批量激活约束，代码更简洁
        NSLayoutConstraint.activate([
            imageView.topAnchor.constraint(equalTo: topAnchor),
            imageView.bottomAnchor.constraint(equalTo: bottomAnchor),
            imageView.leadingAnchor.constraint(equalTo: leadingAnchor, constant: -120),
            imageView.trailingAnchor.constraint(equalTo: trailingAnchor)
        ])
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        guard !animationPlayed else { return }
        animationPlayed = true
        
        // 使用当前Swift语法的transform构造方法，替代已废弃的CGAffineTransformTranslate
        UIView.animate(withDuration: 7.0) {
            self.imageView.transform = CGAffineTransform(translationX: 120, y: 0)
        }
    }
}

解决方案二：在控制器的viewDidAppear中触发动画 #

这种方式更可控，能明确控制动画触发时机：

1. 给Page类添加一个触发动画的方法：

class Page: UIView {
    private let imageView: UIImageView = {
        let image = UIImageView()
        image.image = UIImage(named: "1")
        image.translatesAutoresizingMaskIntoConstraints = false
        return image
    }()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(imageView)
        
        NSLayoutConstraint.activate([
            imageView.topAnchor.constraint(equalTo: topAnchor),
            imageView.bottomAnchor.constraint(equalTo: bottomAnchor),
            imageView.leadingAnchor.constraint(equalTo: leadingAnchor, constant: -120),
            imageView.trailingAnchor.constraint(equalTo: trailingAnchor)
        ])
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    // 暴露动画触发方法
    func startAnimation() {
        UIView.animate(withDuration: 7.0) {
            self.imageView.transform = CGAffineTransform(translationX: 120, y: 0)
        }
    }
}

2. 在OnboardingController的viewDidAppear方法中调用：

class OnboardingController: UIViewController {
    // ... 原有代码 ...
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        views.startAnimation()
    }
}

额外优化点 #

• 用NSLayoutConstraint.activate批量激活约束，替代单独设置isActive，代码更简洁易维护
• 替换已废弃的CGAffineTransformTranslate为CGAffineTransform(translationX:y:)，符合当前Swift语法规范

内容的提问来源于stack exchange，提问作者Alex Smith