滚动时向 UIpageviewcontroller 添加另一个页面并删除前一个页面以防止 memory 泄漏

Question

当我使用 UIPageViewController 时，我遇到了 memory 大泄漏的问题。 我有一个视图，我滚动它。 我看到 memory 增长非常快。

我有一个 ViewController 数组（大约 350+ vc）， UIPageViewcontroller 显示页面中的每个 VC，问题是：

到 append 350+ 数组中的 Viewcontroller 是导致 memory 快速增长所以有没有办法 append VC 在通过 viewController 在数组中滚动之前和查看方法之后？

因此数组将始终为 2 索引，例如

    arraypage1 = [vc1,vc2,vc3]

当滚动到下一页时，arraypage1 是 [vc2,vc3,vc4] 所以索引 0 删除，但新页面将添加到索引 2

这是我到目前为止所做的：

在TestVC：

var TodayDate: String?
var data1 : String? , data2: String?
var data3: String? , data4: String?
var data5: String? , data6: String?
var imagee: UIImage? 

在 UIpageView 控制器：

let vc1 = self.storyboard?.instantiateViewController(withIdentifier: "page1")as! TestPageVC
vc1.TodayDate = "06.09.2022"
vc1.data1 = "welcome"
vc1.data2 = "The first data..."
vc1.data3 = "The first data..."
vc1.data4 = "The first data..."
vc1.data5 = "The first data..."
vc1.data6 = "The first data..."
vc1.imagee = UIImage(named: "0001")

let vc2 = self.storyboard?.instantiateViewController(withIdentifier: "page1")as! TestPageVC
vc2.TodayDate = "07.09.2022"
vc2.data1 = "welcome"
vc2.data2 = "The second data..."
vc2.data3 = "The second data..."
vc2.data4 = "The second data..."
vc2.data5 = "The second data..."
vc2.data6 = "The second data..."
vc2.imagee = UIImage(named: "0002")

let vc3 = self.storyboard?.instantiateViewController(withIdentifier: "page1")as! TestPageVC
vc3.TodayDate = "08.09.2022"
vc3.data1 = "welcome"
vc3.data2 = "The third data..."
vc3.data3 = "The third data..."
vc3.data4 = "The third data..."
vc3.data5 = "The third data..."
vc3.data6 = "The third data..."
vc3.imagee = UIImage(named: "0003")


let vc4 = self.storyboard?.instantiateViewController(withIdentifier: "page1")as! TestPageVC
vc4.TodayDate = "08.09.2022"
vc4.data1 = "welcome"
vc4.data2 = "The fourth data..."
vc4.data3 = "The fourth data..."
vc4.data4 = "The fourth data..."
vc4.data5 = "The fourth data..."
vc4.data6 = "The fourth data..."
vc4.imagee = UIImage(named: "0004")


let vc5 = self.storyboard?.instantiateViewController(withIdentifier: "page1")as! TestPageVC
vc3.TodayDate = "08.09.2022"
vc3.data1 = "welcome"
vc3.data2 = "The fifth data..."
vc3.data3 = "The fifth data..."
vc3.data4 = "The fifth data..."
vc3.data5 = "The fifth data..."
vc3.data6 = "The fifth data..."
vc3.imagee = UIImage(named: "0005")

arraypage1.append(contentsOf:[vc1, vc2, vc3])

// here i want add vc4 and remove vc1 when go to next page 

 func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {



    guard let currentIndex = arraypage2.firstIndex(of: viewController) else {
        return nil
    }
    
    UserDefaults.standard.removeObject(forKey: "emptyView1")

    let previousIndex = currentIndex - 1
    guard previousIndex >= 0 else {
        return nil
    }
    

    
    return arraypage2[previousIndex]
    
    }



  func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

    guard let currentIndex = arraypage2.firstIndex(of: viewController) else {
        return nil
    }
    
    let afterIndex = currentIndex + 1

 
    let afterIndex3 = currentIndex + 2
     if afterIndex3 == arraypage2.count {
      UserDefaults.standard.set("next", forKey: "emptyView1")
    }
    
    
    guard afterIndex < arraypage2.count else {
        return nil
    }


    return arraypage2[afterIndex]
    
}

Answer 1

如您所见，如果您使用具有许多页面的UIPageViewController ，如果您保留一组实例化的视图控制器，您将很快遇到 memory 问题。

为了避免这种情况，我们希望在页面视图 Controller 请求控制器时动态实例化控制器。

这是一个简单的例子......

首先，我们将定义一个数据结构（您可能会有更多属性）：

struct MyPageData {
    var title: String = "Title"
    var subtitle: String = "Subtitle"
    var imgName: String = "0.circle.fill"
    var bkgColor: UIColor = .white
}

接下来我们将在 Storyboard 中布置一个“页面”视图 controller，所以它看起来像这样：

并将其自定义 Class 设置为TestPageVC并为其指定“page1”标识符：

class TestPageVC: UIViewController {
    
    public var pageIndex: Int = 0
    
    @IBOutlet var titleLabel: UILabel!
    @IBOutlet var subtitleLabel: UILabel!
    @IBOutlet var imageView: UIImageView!
    
    func fillData(_ mpd: MyPageData) {
        titleLabel.text = mpd.title
        subtitleLabel.text = mpd.subtitle
        if let img = UIImage(systemName: mpd.imgName) {
            imageView.image = img
        }
        view.backgroundColor = mpd.bkgColor
    }
}

请注意，我们添加了一个pageIndex属性，我们将使用它来跟踪显示的“页面”。

在我们的UIPageViewController中，我们将使用数据结构数组而不是视图控制器数组：

    // array of data -- NOT view controllers
    var pageData: [MyPageData] = []

在viewDidLoad()中，我们将生成 350 个：

class MyDynamicViewController: UIPageViewController {
    
    // array of data -- NOT view controllers
    var pageData: [MyPageData] = []
    
    override func viewDidLoad() {
        super.viewDidLoad()
    
        let colors: [UIColor] = [
            .red, .green, .blue,
            .cyan, .magenta, .yellow,
            .systemRed, .systemGreen, .systemYellow,
        ]
        
        // let's create 350 "pages"
        var mpd: MyPageData
        for i in 0..<350 {
            mpd = MyPageData()
            mpd.title = "Page \(i)"
            mpd.subtitle = "Subtitle for page \(i)"
            mpd.imgName = "\(i % 20).circle.fill"
            mpd.bkgColor = colors[i % colors.count]
            pageData.append(mpd)
        }
        
        dataSource = self
        delegate = nil
        
        // instantiate the first "page"
        guard let sb = storyboard,
              let vc = sb.instantiateViewController(withIdentifier: "page1") as? TestPageVC
        else {
            fatalError("Could not instantiate view controller!")
        }
        vc.loadViewIfNeeded()
        vc.fillData(pageData[0])
        vc.pageIndex = 0

        setViewControllers([vc], direction: .forward, animated: false, completion: nil)
    }
    
}

正如我们在viewDidLoad()末尾看到的那样，我们实例化了第一个“页面”视图 controller 并调用setViewControllers([vc], ...)

现在我们编写UIPageViewControllerDataSource来实例化并返回“页面”视图控制器的新实例，而不是将它们保存在一个巨大的数组中：

// typical Page View Controller Data Source
extension MyDynamicViewController: UIPageViewControllerDataSource {
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        
        guard let vc = viewController as? TestPageVC else { return nil }
        
        if vc.pageIndex == 0 { return nil }
        
        guard let sb = storyboard,
              let newVC = sb.instantiateViewController(withIdentifier: "page1") as? TestPageVC
        else {
            fatalError("Could not instantiate view controller!")
        }
        
        let n = vc.pageIndex - 1
        
        newVC.loadViewIfNeeded()
        newVC.fillData(pageData[n])
        newVC.pageIndex = n

        return newVC
        
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

        guard let vc = viewController as? TestPageVC else { return nil }
        
        if vc.pageIndex >= pageData.count - 1 { return nil }
        
        guard let sb = storyboard,
              let newVC = sb.instantiateViewController(withIdentifier: "page1") as? TestPageVC
        else {
            fatalError("Could not instantiate view controller!")
        }
        
        let n = vc.pageIndex + 1
        
        newVC.loadViewIfNeeded()
        newVC.fillData(pageData[n])
        newVC.pageIndex = n
        
        return newVC

    }
    
}

// typical Page View Controller Delegate
extension MyDynamicViewController: UIPageViewControllerDelegate {
    
    // if you do NOT want the built-in PageControl (the "dots"), comment-out these funcs
    
    func presentationCount(for pageViewController: UIPageViewController) -> Int {
        return pageData.count
    }
    
    func presentationIndex(for pageViewController: UIPageViewController) -> Int {
        guard let firstVC = pageViewController.viewControllers?.first as? TestPageVC else {
            return 0
        }
        return firstVC.pageIndex
    }
    
}