为什么 invalidateLayout 没有在 UICollectionView 中触发 sizeForItemAtIndexPath？ （附代码）

Question

问题是 collectionView 中的列数在旋转时不会保持在 7（所需数量）。需要修改什么代码来解决这个问题？

自定义 UICollectionViewFlowLayout 中的 invalidateLayout 似乎没有触发 collectionView 中的 sizeForItemAtIndexPath 方法？有任何想法吗？我真的只是希望在旋转时通过 sizeForItemAtIndexPath 调整列的大小。

注意：我在这里没有使用故事板，而是有一个自定义视图，我在其中放入一个 collectionView 并引用我自己的 collectionView 类。

以下代码可以正常工作，但是在旋转时，它不会像应有的那样将列数保持为 7。最初运行代码时，控制台输出显示：

GCCalendar - init coder
GCCalendar - commonInit
GCCalendarLayout:invalidateLayout
GCCalendarLayout:invalidateLayout
ViewController:viewWillLayoutSubviews
GCCalendarLayout:invalidateLayout
GCCalendarLayout:prepareLayout
sizeForItemAtIndexPath
.
.
sizeForItemAtIndexPath
minimumInteritemSpacingForSectionAtIndex
minimumLineSpacingForSectionAtIndex
GCCalendarLayout:collectionViewContentSize
GCCalendarLayout:layoutAttributesForElementsInRect
GCCalendarLayout:collectionViewContentSize
ViewController:viewWillLayoutSubviews
GCCalendarCell:drawRect
.
.
GCCalendarCell:drawRect

然后旋转屏幕我看到以下内容：

ViewController:viewWillLayoutSubviews
GCCalendarLayout:shouldInvalidateLayoutForBoundsChange
GCCalendarLayout:invalidateLayout
GCCalendarLayout:prepareLayout
GCCalendarLayout:collectionViewContentSize
GCCalendarLayout:layoutAttributesForElementsInRect
GCCalendarLayout:collectionViewContentSize

所以问题是“sizeForItemAtIndexPath”从未被调用？？？？

轮换输出代码

注意：即使“invalidateLayout”是“sizeForItemAtIndexPath”也不会触发

ViewController:viewWillLayoutSubviews GCCalendarLayout:shouldInvalidateLayoutForBoundsChange GCCalendarLayout:invalidateLayout

**包含集合视图的我的自定义视图**

import UIKit

@IBDesignable class GCCalendarView: UIView {

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }



    // Private

    private func commonInit() {
        if self.subviews.count == 0 {
            let bundle = NSBundle(forClass: self.dynamicType)
            let nib = UINib(nibName: "GCCalendarView", bundle: bundle)
            let view = nib.instantiateWithOwner(self, options: nil)[0] as! UIView
            view.frame = bounds
            view.autoresizingMask = [.FlexibleWidth, .FlexibleHeight]
            addSubview(view)
        }
    }

}

自定义集合视图

import UIKit

class GCCalendar : UICollectionView, UICollectionViewDataSource, UICollectionViewDelegate {

    // Init ---------------

    func commonInit(coder aDecoder: NSCoder) {
        print("GCCalendar - commonInit")
        self.registerClass(GCCalendarCell.self, forCellWithReuseIdentifier: "GCCalendarCell")
        self.dataSource = self
        self.delegate = self

        let layout : GCCalendarLayout = GCCalendarLayout(coder: aDecoder)!
        self.setCollectionViewLayout(layout, animated: false)

        self.backgroundColor = UIColor.whiteColor()
    }

    required init?(coder aDecoder: NSCoder) {
        print("GCCalendar - init coder")
        super.init(coder: aDecoder)
        commonInit(coder: aDecoder)
    }


    // UICollectionViewDelegateFlowLayout ------------

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
        print("sizeForItemAtIndexPath")
        let w : CGFloat = floor(self.frame.size.width/7)
        return CGSize(width: w, height: w)
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAtIndex section: Int) ->
        CGFloat {
        print("minimumInteritemSpacingForSectionAtIndex")
        return 0.0
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -> CGFloat {
        print("minimumLineSpacingForSectionAtIndex")
        return 0.0
    }


    // UICollectionViewDataSource -------------------

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 21
    }

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


        return cell!
    }
}

** 自定义 CollectionView 单元格 **

import UIKit

class GCCalendarCell: UICollectionViewCell {

    @IBOutlet weak var title : UITextField!
    @IBOutlet weak var date: UILabel!

    required init?(coder aDecoder: NSCoder) {
        print("GCCalendarCell - init:coder")
        super.init(coder: aDecoder)
        commonInit()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    override func drawRect(rect: CGRect) {
        print("GCCalendarCell:drawRect")
        self.layer.borderWidth = 1
        self.layer.borderColor = UIColor.grayColor().CGColor
    }

    // Private

    private func commonInit() {
        let bundle = NSBundle(forClass: self.dynamicType)
        let nib = UINib(nibName: "GCCalendarCell", bundle: bundle)
        let view = nib.instantiateWithOwner(self, options: nil)[0] as! UIView
        view.frame = bounds
        view.autoresizingMask = [.FlexibleWidth, .FlexibleHeight]
        addSubview(view)
    }

}

自定义布局

import UIKit

class GCCalendarLayout : UICollectionViewFlowLayout {
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
        print("GCCalendarLayout:shouldInvalidateLayoutForBoundsChange")
        return true
    }

    override func invalidateLayout() {
        print("GCCalendarLayout:invalidateLayout")
        super.invalidateLayout()

    }

    override func prepareForCollectionViewUpdates(updateItems: [UICollectionViewUpdateItem]) {
        print("GCCalendarLayout:prepareForCollectionViewUpdates")
        super.prepareForCollectionViewUpdates(updateItems)
    }

    override func finalizeCollectionViewUpdates() {
        print("GCCalendarLayout:finalizeCollectionViewUpdates")
        super.finalizeCollectionViewUpdates()
    }


}

Answer 1

编辑：在你的 viewController 中试试这个：

override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) 
{
    (self.collectionview.collectionViewLayout).setItemSize(CGSizeMake(floor(size.width / 7), floor(size.width / 7)))
    self.collectionview.collectionViewLayout.invalidateLayout()
}

Answer 2

如果你正在使用 Storyboard 在 Storyboard 中设置 CollectionviewFlowLayout 类，我附上了 Bellow

Answer 3

现有答案对我没有任何帮助（iPhone X Simulator iOS 11.2）。
我发现更改 estimatedSize 可以帮助我解决这个问题：

<...>
//***new line
flowLayout.estimatedItemSize = [self getIconSize];//get a new size for items

[flowLayout invalidateLayout];
<...>

Answer 4

@Kujey的解决方案可以应用到UIView而不访问UIViewController：

func traitCollectionDidChange(previousTraitCollection : UITraitCollection) {
    super.traitCollectionDidChange(previousTraitCollection)
    self.collectionView.collectionViewLayout.invalidateLayout()
}