我正在使用UIPageViewController
编写一个iOS应用程序。我的 Root View Controller 是 ViewController,我在其下添加了 UIPageViewController 作为子 VC。
最初,我将 ViewController
作为页面 View VC 委托(delegate):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 ")
}
}
}
}
}
这个方法效果很好。直到我决定将委托(delegate)功能移至专用类:
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:函数 pageViewController(_: didFinishAnimating:previousViewControllers:transitionCompleted)
根本没有被调用,尽管我确实将委托(delegate)设置为这个新类的实例。
我唯一能想到的是,新的委托(delegate)对象不再是 VC(它曾经是我的主 VC)。所以我怀疑这种行为变化与 VC 层次结构有关?
我是不是错过了什么?
最佳答案
(这个答案的灵感来自于 OOPer 的评论)。
发现原因是因为最初我只保留了对委托(delegate)对象的弱
引用。像这样:
之前:
class ViewController: UIViewController {
init() {
self.pageViewController.delegate = PeoplePageViewDelegate(….)
}
}
这里的问题是,一旦执行点通过了 init
方法范围,PeoplePageViewDelegate
就会被垃圾回收,因为它的引用计数为零。
我是如何解决这个问题的:
我在 ViewController
中添加了一个强引用作为字段,以便它将保留委托(delegate)对象:
之后:
class ViewController: UIViewController {
var myStrongReference: PeoplePageViewDelegate?
init() {
self.myStrongReference = PeoplePageViewDelegate(….)
self.pageViewController.delegate = self.myStrongReference
}
}
关于ios - 如何为 UIPageViewController Delegate 创建自定义类?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/54576324/