自定义转场切换到UINavigationController后Push控制器布局异常

1. View层级与Safe Area绑定异常
   转场动画时，目标ViewController（如UINavigationController）的view被直接添加到当前VC的view内部，而非window层级。这导致目标VC的view无法正确关联window的safe area上下文，后续push的VC自然会出现safe area失效问题。

2. 残留的视图变换干扰
   动画过程中对当前VC的view设置了transform、alpha等属性，替换rootViewController后未重置这些状态。残留的变换会破坏导航控制器内部的动画计算逻辑，导致push无动画。

3. ViewController生命周期触发不完整
   目标VC的view仅作为临时子view存在时，其完整生命周期方法（如viewWillAppear）未正确触发，导致UINavigationController的内部状态初始化异常，进一步引发导航动画失效。

1. 修正replace方法，清理残留状态 #

修改私有方法，确保重置当前VC的视图状态并清理无用视图：

private func replace(with: UIViewController, completion: (() -> Void)?) {
    guard let baseWindow = self.view.window, baseWindow.rootViewController == self else {
        completion?()
        return
    }
    
    // 重置当前视图的所有变换与透明度
    self.view.transform = .identity
    self.view.alpha = 1
    self.view.subviews.forEach { $0.alpha = 1 }
    
    // 移除动画中添加的临时背景视图
    baseWindow.subviews.forEach { subview in
        if subview.backgroundColor == self.view.backgroundColor 
            && subview != self.view 
            && subview != with.view {
            subview.removeFromSuperview()
        }
    }
    
    // 设置新的根控制器并清理旧视图
    baseWindow.rootViewController = with
    self.view.removeFromSuperview()
    
    completion?()
}

2. 统一所有动画的View层级添加逻辑 #

所有动画场景中，将目标VC的view添加到window层级，并确保frame正确：

示例：修正fade动画 #

case .fade:
    guard let window = self.view.window else { 
        replace(with: to, completion: completion)
        return
    }
    // 触发目标VC的view加载，确保生命周期正常
    _ = to.view
    to.view.frame = window.bounds
    to.view.alpha = 0
    window.insertSubview(to.view, aboveSubview: self.view)
    
    UIView.animate(withDuration: 0.3, delay: 0.0, options: [.curveEaseOut], animations: {
        to.view.alpha = 1
    }, completion: { [self] _ in replace(with: to, completion: completion) })

示例：修正slide(.left)动画 #

case .slide(.left):
    guard let window = self.view.window else { 
        replace(with: to, completion: completion)
        return
    }
    let width = window.bounds.width
    _ = to.view
    to.view.frame = window.bounds
    to.view.transform = CGAffineTransform(translationX: width, y: 0)
    window.insertSubview(to.view, aboveSubview: self.view)

    UIView.animate(withDuration: 0.7, delay: 0.0, usingSpringWithDamping: 0.8, initialSpringVelocity: 0.2, options: [.curveEaseInOut], animations: { [self] in
        self.view.transform = CGAffineTransform(translationX: -width, y: 0)
        self.view.subviews.forEach({ $0.alpha = 0 })
        to.view.transform = .identity
    }, completion: { [self] _ in replace(with: to, completion: completion) })

注意：所有其他动画（pageIn、pageOut、zoomIn、zoomOut）都需要按照此逻辑修改，将self.view.superview?.insertSubview替换为window.insertSubview，并提前设置目标view的frame。

3. 移除冗余的layoutIfNeeded调用 #

原代码中部分动画里的self.view.layoutIfNeeded()属于冗余操作，因为当前VC即将被替换，无需再触发其布局，可直接删除这些调用。

修改后，执行以下流程：

1. VC1调用transition.to(NC1, animation: .fade)
2. VC2调用self.navigationController?.pushViewController(VC3, animated: true)
   此时VC3的safe area会正常适配，push动画也能正常触发。

内容的提问来源于stack exchange，提问作者CristianMoisei