Question

我正在使用UIPageViewController编写iOS应用。我的根视图控制器是ViewController，我在其下添加了UIPageViewController作为子VC。

最初，我将ViewController设为页面视图VC委托：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 ")
                }
            }
        }


    }
}

这样可以正常工作。直到我决定将委托功能移到专用的类上为止：

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：尽管我确实将委托设置为这个新类的实例，但根本没有调用函数pageViewController(_: didFinishAnimating:previousViewControllers:transitionCompleted)。

我唯一能想到的是，新的委托对象不再是VC（它曾经是我的主要VC）。因此，我怀疑这种行为变化与VC层级有关吗？

我错过了什么吗？

Answer 1

（此答案受OOPer的评论启发）。

发现原因是因为最初我仅保留对委托对象的'at this point the dictionary is already populated similar to 'dict.Add 'ID_01', Array('val1', 'val2', 'val3') dim i as long, arr as variant with sheet a arr = .range(.cells(2, "A"), .cells(.rows.count, "A").end(xlup)).value2 redim preserve arr(lbound(arr, 1) to ubound(arr, 1), 1 to 4) 'if sheet A already has values that only require updating, 'then use this instead 'arr = .range(.cells(2, "A"), .cells(.rows.count, "A").end(xlup).offset(0, 3)).value2 for i=lbound(arr, 1) to ubound(arr, 1) If dict.exists(arr(i, 1)) Then arr(i, 2) = dict.Item(arr(i, 1))(0) arr(i, 3) = dict.Item(arr(i, 1))(1) arr(i, 4) = dict.Item(arr(i, 1))(2) end if next i .cells(2, "A").resize(ubound(arr, 1), ubound(arr, 2)) = arr end with引用。像这样：

之前：

weak

这里的问题是一旦执行点通过了class ViewController: UIViewController { init() { self.pageViewController.delegate = PeoplePageViewDelegate(….) } }方法范围，init就被垃圾回收了，因为它的引用计数为零。

我如何修复它：

我在PeoplePageViewDelegate中添加了一个强引用作为字段，以便保留委托对象：

之后：

ViewController

如何为UIPageViewControllerDelegate创建自定义类？

1 个答案: