如何在 UIScrollView 中調用嵌入式 ViewControllers 生命周期 - Swift - 以編程方式

Question

我正在創建一個滾動視圖，它能夠一個接一個地顯示 ViewController 視圖。 這是我實現的代碼：

scrollView.contentSize = CGSize(width: screenWidth * 3, height: screenHeight)
    
    let firstVC = FirstViewController()
    
    let secondVC = SecondViewController()
    
    let thirdVC = ThirdViewController()
    
    self.addChild(firstVC)
    self.scrollView.addSubview(firstVC.view)
    firstVC.willMove(toParent: self)
    
    self.addChild(secondVC)
    self.scrollView.addSubview(secondVC.view)
    secondVC.willMove(toParent: self)

    self.addChild(thirdVC)
    self.scrollView.addSubview(thirdVC.view)
    thirdVC.willMove(toParent: self)
    
    
    firstVC.view.frame.origin = CGPoint.zero
    secondVC.view.frame.origin = CGPoint(x: screenWidth, y: 0)
    thirdVC.view.frame.origin = CGPoint(x: screenWidth*2, y: 0)
    
    
    view.addSubview(scrollView)
    scrollView.fillSuperview()

我想知道是否可以在我滾動瀏覽每個 ViewController 生命周期方法時調用它們。

例如，當我從 vc1 傳遞到 vc2 時，我想要：

vc1 觸發 viewwillDisappear 方法

vc2 觸發 viewWillAppear 方法

Answer 1

最簡單的解決方案是使用頁面視圖控制器。 當你這樣做時，子項的外觀方法將自動為你調用（它讓你擺脫所有密集的代碼來手動填充和配置滾動視圖）：

class MainViewController: UIPageViewController {
    let controllers = [RedViewController(), GreenViewController(), BlueViewController()]

    override func viewDidLoad() {
        super.viewDidLoad()

        dataSource = self
        setViewControllers([controllers.first!], direction: .forward, animated: true, completion: nil)
    }
}

extension MainViewController: UIPageViewControllerDataSource {
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        if let index = controllers.firstIndex(where: { $0 == viewController }), index < (controllers.count - 1) {
            return controllers[index + 1]
        }
        return nil
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        if let index = controllers.firstIndex(where: { $0 == viewController }), index > 0 {
            return controllers[index - 1]
        }
        return nil
    }
}

如果你真的想使用滾動視圖方法，不要預先編寫視圖控制器包含代碼，而只是在它們滾動到視圖時添加它們（並在它們滾動出視圖時刪除它們）。 你只需要為你的滾動視圖設置一個委托並實現一個UIScrollViewDelegate方法。

因此，例如，我可能只使用這三個子視圖控制器的容器子視圖填充我的滾動視圖。 （注意我下面示例中的containerViews只是空白的UIView實例，布置在子視圖控制器視圖最終會去的地方。）然后我可以查看滾動視圖可見部分的CGRect是否與容器視圖相交，然后執行以即時方式包含視圖控制器。

extension ViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let rect = CGRect(origin: scrollView.contentOffset, size: scrollView.bounds.size)
        for (index, containerView) in containerViews.enumerated() {
            let controller = controllers[index]
            let controllerView = controller.view!
            if rect.intersects(containerView.frame) {
                if controllerView.superview == nil {
                    // a container view has scrolled into view, but the associated
                    // child controller view has not been added to the view hierarchy, yet
                    // so let's do that now

                    addChild(controller)
                    containerView.addSubview(controllerView)
                    controllerView.translatesAutoresizingMaskIntoConstraints = false

                    NSLayoutConstraint.activate([
                        controllerView.topAnchor.constraint(equalTo: containerView.topAnchor),
                        controllerView.bottomAnchor.constraint(equalTo: containerView.bottomAnchor),
                        controllerView.leadingAnchor.constraint(equalTo: containerView.leadingAnchor),
                        controllerView.trailingAnchor.constraint(equalTo: containerView.trailingAnchor)
                    ])

                    controller.didMove(toParent: self)
                }
            } else {
                if controllerView.superview != nil {
                    // a container view has scrolled out of view, but the associated
                    // child controller view is still in the view hierarchy, so let's
                    // remove it.

                    controller.willMove(toParent: nil)
                    controllerView.removeFromSuperview()
                    controller.removeFromParent()
                }
            }
        }
    }
}

在這兩種情況下，您將在視圖出現時收到遏制調用。