iOS 2个Controller 切换

效果如下

在First和Second上2个按钮点击调用switchover()

weak var currentViewController :UIViewController!
override func viewDidLoad() {
        super.viewDidLoad()
                
        currentViewController = FirstViewController()
        self.addChildViewController(currentViewController)
        self.view.addSubview(currentViewController.view)
}

private var first :Bool = true
//按钮点击事件
func switchover(){
       let toVc = first ? SecondViewController() : FirstViewController()
       self.addChildViewController(toVc)
        
        toVc.view.top = UIScreen.main.bounds.height
        self.transition(from: currentViewController, to: toVc, duration: 0.25, options: .curveLinear, animations: {
            toVc.view.top = 0
        }, completion: { finish in
            self.currentViewController.didMove(toParentViewController: self)
            self.currentViewController.removeFromParentViewController()
            self.currentViewController = toVc
        })
        self.first = !first
}

动画可以自己修改，也可以支持多个控制器，自己维护ChildViewControllers。最好不要让ViewController长期持有子控制器，对内存不够友好。