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，单元格没有得到更新。

我找到了一个函数，它会在方向改变时调用：

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

但我找不到更新 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()
}

当你改变方向时，这个函数会被调用。

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些：

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。

其中一种工作方式是

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。可以直接重写方法。UICollectionLayout可以适时调用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

traitCollectionDidChange(previousTraitCollection :) 旋转时不会在 iPad 上调用，因为尺寸类在纵向和横向都是 .regular 。每当集合视图大小发生变化时都会调用 viewWillTransition(to:with:)。

此外，如果您的应用支持多任​​务处理，则不应使用 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

我的代码：

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

会正常工作！！！

Answer 9

调用viewWillLayoutSubviews 不是最佳选择。尝试先调用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。 （参见示例代码中的可选步骤）

这里是代码，可以帮助您入门。根据创建 UI 的方式，您可能需要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 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项目大小的单元格并将索引路径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

我用下面的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

除了其他人已经提到的，如果你自己创建集合视图而不是继承 UICollectionViewController，不要忘记设置：

collectionView.translatesAutoresizingMaskIntoConstraints = false

设置约束时。

Answer 16

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
  }

}

文档：

此属性的默认值为 false。如果您因更改任何项目的大小而使布局无效，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。