如何使UIPageViewControllerDelegate自定义类？

Question

我写了UIPageViewController的iOS应用。我的根视图控制器是ViewController，我在它之下添加UIPageViewController作为一个孩子的VC。

起初，我做了我ViewController在页面视图VC代表：UIPageViewControllerDelegate：

extension ViewController: UIPageViewControllerDelegate {



    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {

        // set the pageControl.currentPage to the index of the current viewController in pages
        if let viewControllers = pageViewController.viewControllers as? [UIViewController] {
            if let viewControllerIndex = self.detailPagedVC.pages.index(of: viewControllers[0]) {
                self.detailPagedVC.pageControl.currentPage = viewControllerIndex

                // if current page is a single person view controller, zoom to that person's face
                if let singlePersonViewController = self.detailPagedVC.pages[viewControllerIndex] as? SinglePersonPageViewController {

                    // print("didFinishAnimating: \(viewControllerIndex)")
                    self.zoomableImageVC.zoomableImageView.zoom(to: self.identificationResults[viewControllerIndex].face.rect, with: Constants.contentSpanRatio, animated: true)
                } else if let summaryPageViewController = self.detailPagedVC.pages[viewControllerIndex] as? SummaryPageViewController {
                    self.zoomableImageVC.zoomableImageView.zoom(to: self.zoomableImageVC.zoomableImageView.imageView.bounds, with: Constants.contentSpanRatio, animated: true)
                } else {
                    print("gw: err: unkown type of page controller in paged view ")
                }
            }
        }


    }
}

这种方式工作得很好。直到我决定委派功能移动到专用类：

class PeoplePageViewDelegate: NSObject, UIPageViewControllerDelegate{

    private struct Constants {

        // the ratio of the content (e..g face) taken inside the entire view
        static let contentSpanRatio: CGFloat = 0.8

    }

    // store a reference to the object which will take the actual action
    // action 1: zooming
    weak var zoomingActionTaker: ZoomableImageView?

    // action 2: paging
    weak var pagingActionTaker: PeoplePageViewController?


    // the delegator who relies on this object
    unowned let delegator: PeoplePageViewController

    init(delegator: PeoplePageViewController) {
        self.delegator = delegator

        // wire back to delegator 
        // self.pagingActionTaker = delegator // gw: mind the nuance difference, you chain a weak ref on a unowned ref, what can go wrong?

        super.init()
    }




    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        print("gw:0")
        // set the pageControl.currentPage to the index of the current viewController in pages
        if let viewControllers = pageViewController.viewControllers as? [UIViewController] {
            print("gw:1")
            if let viewControllerIndex = self.delegator.pages.index(of: viewControllers[0]) {
                 print("gw:2")
                self.pagingActionTaker?.pageControl.currentPage = viewControllerIndex

                // if current page is a single person view controller, zoom to that person's face
                if let singlePersonViewController = self.delegator.pages[viewControllerIndex] as? SinglePersonPageViewController {

                     print("gw:3")
                    self.zoomingActionTaker?.zoom(to: singlePersonViewController.identification.face.rect, with: Constants.contentSpanRatio, animated: true)


                } else if let summaryPageViewController = self.delegator.pages[viewControllerIndex] as? SummaryPageViewController,

                    let entireImageBounds = self.zoomingActionTaker?.imageView.bounds {
                    print("gw:4")
                    self.zoomingActionTaker?.zoom(to: entireImageBounds, with: Constants.contentSpanRatio, animated: true)
                } else {
                    print("gw: err: unkown type of page controller in paged view ")
                }
            }
        }


    }
}

这会导致问题：功能pageViewController(_: didFinishAnimating:previousViewControllers:transitionCompleted)不叫可言，尽管我没有设置委托给这个新类的实例。

我能想到的唯一的事情，就是新的委托对象不是VC了（这曾经是我的主要VC）。所以我怀疑是行为的这种变化是关系到VC层次结构？

我错过了什么？

Answer 1

（此答案由OOPer的评论启发）。

结果发现，起因是因为最初我只存weak参考委托对象。像这样：

之前：

class ViewController:  UIViewController { 
    init() {

        self.pageViewController.delegate = PeoplePageViewDelegate(….)


    }

}

这里的问题是，一旦执行点去传递init法范围内，PeoplePageViewDelegate被垃圾回收，因为它的引用计数为零。

我如何固定它：

我添加了一个有力的参考，如我ViewController一个字段，这样它会保留委托对象：

后：

class ViewController:  UIViewController { 

    var myStrongReference: PeoplePageViewDelegate?
    init() {

        self.myStrongReference = PeoplePageViewDelegate(….)

        self.pageViewController.delegate = self.myStrongReference

    }

}