Swift：如何在设备旋转后刷新 UICollectionView 布局

Question

我使用 UICollectionView (flowlayout) 构建了一个简单的布局。 使用self.view.frame.width将每个单元格的宽度设置为屏幕宽度

但是当我旋转设备时，单元格不会更新。

我找到了一个 function，它在方向改变时被调用：

override func willRotateToInterfaceOrientation(toInterfaceOrientation: 
  UIInterfaceOrientation, duration: NSTimeInterval) {
    //code
}

但我无法找到更新 UICollectionView 布局的方法

主要代码在这里：

class ViewController: UIViewController , UICollectionViewDelegate , UICollectionViewDataSource , UICollectionViewDelegateFlowLayout{

    @IBOutlet weak var myCollection: UICollectionView!

    var numOfItemsInSecOne: Int!
    override func viewDidLoad() {
        super.viewDidLoad()

        numOfItemsInSecOne = 8
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func willRotateToInterfaceOrientation(toInterfaceOrientation: UIInterfaceOrientation, duration: NSTimeInterval) {

        //print("orientation Changed")
    }

    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return numOfItemsInSecOne
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cellO", forIndexPath: indexPath)

        return cell
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize{
    let itemSize = CGSize(width: self.view.frame.width, height: 100)
    return itemSize
    }}

Answer 1

添加此功能：

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews() 
    myCollection.collectionViewLayout.invalidateLayout()
}

当您更改方向时，将调用此函数。

Answer 2

更好的选择是调用invalidateLayout()而不是reloadData()因为它不会强制重新创建单元格，因此性能会稍微好一点：

override func viewWillLayoutSubviews() {
    super.viewWillLayoutSubviews() 
    myCollection.collectionViewLayout.invalidateLayout()
}

Answer 3

您也可以通过这种方式使其无效。

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
    [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];

    [self.collectionView.collectionViewLayout invalidateLayout]; 
}

Answer 4

viewWillLayoutSubviews() 对我不起作用。 viewDidLayoutSubviews() 也没有。 两者都使应用程序进入无限循环，我使用打印命令进行了检查。

工作的方法之一是

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
// Reload here
}

Answer 5

要更新UICollectionViewLayout ，也可以使用traitCollectionDidChange方法：

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)

    guard previousTraitCollection != nil else { return }
    collectionView?.collectionViewLayout.invalidateLayout()
}

Answer 6

当UICollectionLayout检测到边界更改时，它会询问是否需要重新路由 Invalidate 布局。 您可以直接重写该方法。 UICollectionLayout可以在适当的时候调用invalidateLayout方法

class CollectionViewFlowLayout: UICollectionViewFlowLayout{
    
    /// The default implementation of this method returns false.
    /// Subclasses can override it and return an appropriate value
    /// based on whether changes in the bounds of the collection
    /// view require changes to the layout of cells and supplementary views.
    /// If the bounds of the collection view change and this method returns true,
    /// the collection view invalidates the layout by calling the invalidateLayout(with:) method.
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        
        return (self.collectionView?.bounds ?? newBounds) != newBounds
    }
}

Answer 7

请理解这一点

traitCollectionDidChange(previousTraitCollection :) 在 iPad 旋转时不会被调用，因为尺寸类在纵向和横向都是 .regular 。 只要集合视图大小发生变化，就会调用 viewWillTransition(to:with:) 。

此外，如果您的应用程序支持多任务处理，您不应该使用 UIScreen.mainScreen().bounds，因为它可能不会占据整个屏幕，最好使用 collectionView.frame.width。

Answer 8

调用viewWillLayoutSubviews不是最佳选择。 首先尝试调用invalidateLayout()方法。

如果您遇到The behaviour of the UICollectionViewFlowLayout is not defined错误，您需要根据新布局验证视图中的所有元素是否已更改其大小。 （请参阅示例代码中的可选步骤）

这是代码，让你开始。 根据创建 UI 的方式，您可能必须尝试找到正确的视图来调用recalculate方法，但这应该会引导您迈出第一步。

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {

    super.viewWillTransition(to: size, with: coordinator)

    /// (Optional) Additional step 1. Depending on your layout, you may have to manually indicate that the content size of a visible cells has changed
    /// Use that step if you experience the `the behavior of the UICollectionViewFlowLayout is not defined` errors.

    collectionView.visibleCells.forEach { cell in
        guard let cell = cell as? CustomCell else {
            print("`viewWillTransition` failed. Wrong cell type")
            return
        }

        cell.recalculateFrame(newSize: size)

    }

    /// (Optional) Additional step 2. Recalculate layout if you've explicitly set the estimatedCellSize and you'll notice that layout changes aren't automatically visible after the #3

    (collectionView.collectionViewLayout as? CustomLayout)?.recalculateLayout(size: size)


    /// Step 3 (or 1 if none of the above is applicable)

    coordinator.animate(alongsideTransition: { context in
        self.collectionView.collectionViewLayout.invalidateLayout()
    }) { _ in
        // code to execute when the transition's finished.
    }

}

/// Example implementations of the `recalculateFrame` and `recalculateLayout` methods:

    /// Within the `CustomCell` class:
    func recalculateFrame(newSize: CGSize) {
        self.frame = CGRect(x: self.bounds.origin.x,
                            y: self.bounds.origin.y,
                            width: newSize.width - 14.0,
                            height: self.frame.size.height)
    }

    /// Within the `CustomLayout` class:
    func recalculateLayout(size: CGSize? = nil) {
        estimatedItemSize = CGSize(width: size.width - 14.0, height: 100)
    }

    /// IMPORTANT: Within the `CustomLayout` class.
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {

        guard let collectionView = collectionView else {
            return super.shouldInvalidateLayout(forBoundsChange: newBounds)
        }

        if collectionView.bounds.width != newBounds.width || collectionView.bounds.height != newBounds.height {
            return true
        } else {
            return false
        }
    }

Answer 9

我的代码：

override func viewWillLayoutSubviews() {
   super.viewWillLayoutSubviews()
   self.collectionView.collectionViewLayout.invalidateLayout()
}

会正常工作！！！

Answer 10

您可以使用更新您的 UICollectionView 布局

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    if isLandscape {
        return CGSizeMake(yourLandscapeWidth, yourLandscapeHeight)
    }
    else {
        return CGSizeMake(yourNonLandscapeWidth, yourNonLandscapeHeight)
    }
}

Answer 11

它对我有用。 这是 Objective-C 中的代码：

- (void)viewDidLayoutSubviews {
  [super viewDidLayoutSubviews];
  [collectionView.collectionViewLayout invalidateLayout];
}

Answer 12

我也遇到了一些问题，但后来使用以下方法解决了：

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        collectionViewFlowLayoutSetup(with: view.bounds.size.width)
        collectionView?.collectionViewLayout.invalidateLayout()
        collectionViewFlowLayoutSetup(with: size.width)
    }

    fileprivate func collectionViewFlowLayoutSetup(with Width: CGFloat){

        if let flowLayout = collectionViewLayout as? UICollectionViewFlowLayout {
            flowLayout.estimatedItemSize = CGSize(width: Width, height: 300)
        }

    }

Answer 13

我通过在屏幕方向更改时设置通知并重新加载根据屏幕方向设置 itemsize 并将 indexpath 设置为前一个单元格来解决此问题。 这也适用于 flowlayout。 这是我写的代码：

var cellWidthInLandscape: CGFloat = 0 {
    didSet {
        self.collectionView.reloadData()
    }
}

var lastIndex: Int = 0

override func viewDidLoad() {
    super.viewDidLoad()

    collectionView.dataSource = self
    collectionView.delegate = self
    NotificationCenter.default.addObserver(self, selector: #selector(rotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
    cellWidthInLandscape = UIScreen.main.bounds.size.width

}
deinit {
    NotificationCenter.default.removeObserver(self)
}
@objc func rotated() {

        // Setting new width on screen orientation change
        cellWidthInLandscape = UIScreen.main.bounds.size.width

       // Setting collectionView to previous indexpath
        collectionView.scrollToItem(at: IndexPath(item: lastIndex, section: 0), at: .right, animated: false)
}
    override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        NotificationCenter.default.addObserver(self, selector: #selector(rotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)

}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {

   // Getting last contentOffset to calculate last index of collectionViewCell
    lastIndex = Int(scrollView.contentOffset.x / collectionView.bounds.width)
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        // Setting new width of collectionView Cell
        return CGSize(width: cellWidthInLandscape, height: collectionView.bounds.size.height)

}

Answer 14

我使用以下方法解决了这个问题

override func viewDidLayoutSubviews() {
        if let flowLayout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
            collectionView.collectionViewLayout.invalidateLayout()
            collectionView.collectionViewLayout = flowLayout
        }
    }

Answer 15

 override func viewWillLayoutSubviews() {
     super.viewWillLayoutSubviews()      
     yourCollectionView?.setCollectionViewLayout(UICollectionViewLayout(), animated: true)
}

Answer 16

除了其他人已经提到的内容之外，如果您自己创建集合视图而不是继承 UICollectionViewController，请不要忘记设置：

collectionView.translatesAutoresizingMaskIntoConstraints = false

设置约束时。

Answer 17

同时，在横向更改为纵向方向后，所选单元格未居中。 我这样解决这个问题：

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
    super.viewWillTransition(to: size, with: coordinator)

    //Scroll to current Item after the orientation change. Sometimes the current item is not centered.
    coordinator.animate(alongsideTransition: { context in
        self.housesCollectionView.collectionViewLayout.invalidateLayout()
        self.housesCollectionView.scrollToItem(at: self.selectedHouseIndexPath, at: .left, animated: true)
    })
}

Answer 18

试试这个：

class CollectionViewFlowLayout: UICollectionViewFlowLayout {

override func invalidationContext(forBoundsChange newBounds: CGRect) -> UICollectionViewLayoutInvalidationContext {
    let context = super.invalidationContext(forBoundsChange: newBounds) as! UICollectionViewFlowLayoutInvalidationContext
    if let collectionView = collectionView {
        context.invalidateFlowLayoutDelegateMetrics = collectionView.bounds.size != newBounds.size
    }
    return context
  }

}

文件：

此属性的默认值为 false。 如果由于任何项目的大小更改而使布局无效，请将此属性设置为 true。 当此属性设置为 true 时，流布局对象会重新计算其项目和视图的大小，并根据需要查询委托对象以获取该信息。