IOS在同一屏幕上的子viewControllers之间转换

import UIKit

class FirstViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Customize the view accordingly
    }
}

class SecondViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Customize the view accordingly
    }
}

class ViewController: UIViewController, UIViewControllerTransitionCoordinator {
    let firstViewController = FirstViewController()
    let secondViewController = SecondViewController()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Add the first and second view controllers
        addChildViewController(firstViewController)
        addChildViewController(secondViewController)
        
        // Set the initial view controller
        setViewControllers([firstViewController], direction: .forward, animated: true, completion: nil)
    }
}

import UIKit

class FirstViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Customize the view accordingly
    }
}

class SecondViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Customize the view accordingly
    }
}

class ViewController: UIViewController {
    let firstViewController = FirstViewController()
    let secondViewController = SecondViewController()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Add the first and second view controllers
        addChildViewController(firstViewController)
        addChildViewController(secondViewController)
        
        // Set the initial view controller
        setViewControllers([secondViewController], direction: .forward, animated: true, completion: nil)
        
        // Add the first and second view controllers to the container view
        let containerView = UIView(frame: view.frame)
        addSubview(containerView)
        
        containerView.addSubview(firstViewController.view)
        containerView.addSubview(secondViewController.view)
    }
}

override func viewDidLoad() {

    super.viewDidLoad()

    // Customize the view accordingly

}

override func viewDidLoad() {

    super.viewDidLoad()

    // Customize the view accordingly

}

let firstViewController = FirstViewController()

let secondViewController = SecondViewController()

override func viewDidLoad() {

    super.viewDidLoad()

    // Add the first and second view controllers

    addChildViewController(firstViewController)

    addChildViewController(secondViewController)

    // Set the initial view controller

    setViewControllers([secondViewController], direction: .forward, animated: true, completion: nil)

    // Add the first and second view controllers to the container view

    let containerView = UIView(frame: view.frame)

    addSubview(containerView)

    containerView.addSubview(firstViewController.view)

    containerView.addSubview(secondViewController.view)

    // Add the custom transition view to the container view

    let transitionView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))

    transitionView.backgroundColor = UIColor.red

    containerView.addSubview(transitionView)

    // Present the second view controller

    secondViewController.view.frame = view.frame

    secondViewController.view.alpha = 0

    transitionView.frame = CGRect(