ios - collectionView 中的异常(_ :layout:sizeForItemAt:) when accessing layout. collectionViewContentSize

Question

实现

我想在 UICollectionView 中拥有两种不同的项目大小。因此我已经实现了

UICollectionViewDelegateFlowLayout 的 collectionView(_:layout:sizeForItemAt:)。

错误

但我遇到的问题是，每当我在此函数中访问 collectionViewLayout.collectionViewContentSize 时，我的应用程序都会崩溃并出现异常。

异常(exception)情况如下:

* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayM objectAtIndexedSubscript:]: index 1 beyond bounds [0 .. 0]'.

抛出调用堆栈位于帖子底部。

看来是SDK的内部问题，可能是某些东西没有正确初始化!？

问题

任何人都可以确认此错误或告诉我我做错了什么吗？

实现

这是我对 UICollectionViewDelegateFlowLayout 的实现:

class TwoSizesCellFlowLayout: NSObject, UICollectionViewDelegateFlowLayout {

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let layoutSize = collectionViewLayout.collectionViewContentSize // CRASHES when accessing `collectionViewContentSize`
        // SDK error?
        let layoutSize = collectionView.contentSize // works but results in slightly different size
        var size = layoutSize.width / 2

        if let flowLayout = collectionViewLayout as? UICollectionViewFlowLayout {
            size = size - flowLayout.minimumInteritemSpacing / 2
        }
        return CGSize(width: size, height: size)
    }
}

在 Collection View Controller 子类中，我将 TwoSizesCellFlowLayout 对象分配给 UICollectionViewController 的 delegate 属性:

class ViewController: UICollectionViewController {

    ...

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        collectionView?.dataSource = self
        collectionView?.delegate = collectionViewDelegateAndLayout

        let nib = UINib.init(nibName: "BasicCollectionViewCell", bundle: nil)
        collectionView?.register(nib, forCellWithReuseIdentifier: cellIdentifier)

        // accessing `collectionViewContentSize` here works like a charm, but only one size for all items is possible
//        let collectionViewSize = collectionView?.collectionViewLayout.collectionViewContentSize
//        if let collectionSize = collectionViewSize, let flowLayout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
//            let size = collectionSize.width / 2 - flowLayout.minimumInteritemSpacing / 2
//            let cellSize = CGSize(width: size, height: size)
//            flowLayout.itemSize = cellSize
//        }
    }

    ...

}

第一次抛出调用堆栈:

0   CoreFoundation                      0x00000001117751e6 __exceptionPreprocess + 294
1   libobjc.A.dylib                     0x000000010d946031 objc_exception_throw + 48
2   CoreFoundation                      0x00000001117b50bc _CFThrowFormattedException + 194
3   CoreFoundation                      0x00000001117a67b1 -[__NSArrayM objectAtIndexedSubscript:] + 177
4   UIKit                               0x000000010ecf2957 -[UICollectionViewFlowLayout _getSizingInfosWithExistingSizingDictionary:] + 1801
5   UIKit                               0x000000010ecf47db -[UICollectionViewFlowLayout _fetchItemsInfoForRect:] + 136
6   UIKit                               0x000000010eced70a -[UICollectionViewFlowLayout collectionViewContentSize] + 66
7   _blackened_                             0x000000010d28812f _T07beSmart22TwoSizesCellFlowLayoutC14collectionViewSC6CGSizeVSo012UICollectionI0C_So0kiG0C6layout10Foundation9IndexPathV13sizeForItemAttF + 79
8   _blackened_                             0x000000010d2882fa _T07beSmart22TwoSizesCellFlowLayoutC14collectionViewSC6CGSizeVSo012UICollectionI0C_So0kiG0C6layout10Foundation9IndexPathV13sizeForItemAttFTo + 122
9   UIKit                               0x000000010ecf2e50 -[UICollectionViewFlowLayout _getSizingInfosWithExistingSizingDictionary:] + 3074
10  UIKit                               0x000000010ecf47db -[UICollectionViewFlowLayout _fetchItemsInfoForRect:] + 136
11  UIKit                               0x000000010eced104 -[UICollectionViewFlowLayout prepareLayout] + 272
12  UIKit                               0x000000010ed1a0a9 -[UICollectionViewData _prepareToLoadData] + 156
13  UIKit                               0x000000010ed1a956 -[UICollectionViewData validateLayoutInRect:] + 53
14  UIKit                               0x000000010ecb0620 -[UICollectionView layoutSubviews] + 260
15  UIKit                               0x000000010e2b17a8 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1515
16  QuartzCore                          0x0000000114d45456 -[CALayer layoutSublayers] + 177
17  QuartzCore                          0x0000000114d49667 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 395
18  QuartzCore                          0x0000000114cd00fb _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 343
19  QuartzCore                          0x0000000114cfd79c _ZN2CA11Transaction6commitEv + 568
20  QuartzCore                          0x0000000114cfe51a _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 76
21  CoreFoundation                      0x0000000111717607 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
22  CoreFoundation                      0x000000011171755e __CFRunLoopDoObservers + 430
23  CoreFoundation                      0x00000001116fbb81 __CFRunLoopRun + 1537
24  CoreFoundation                      0x00000001116fb30b CFRunLoopRunSpecific + 635
25  GraphicsServices                    0x0000000113ecea73 GSEventRunModal + 62
26  UIKit                               0x000000010e1e2057 UIApplicationMain + 159
27  _blackened_                             0x000000010d2896c7 main + 55
28  libdyld.dylib                       0x00000001127b7955 start + 1

问候，

亚伦

Answer 1

问题已解决。

我认为问题在于调用 collectionView(_:layout:sizeForItemAt:) 来确定 collectionViewContentSize 属性。但我尝试访问其中的collectionViewContentSize。

我使用collectionView的bounds修复了它。

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let viewSize = collectionView.bounds.size
    var cellWidth = viewSize.width / 2

    if let flowLayout = collectionViewLayout as? UICollectionViewFlowLayout {
        let usableViewWidth = viewSize.width - flowLayout.sectionInset.left - flowLayout.sectionInset.right
        cellWidth = usableViewWidth / 2 - flowLayout.minimumInteritemSpacing / 2
    }
    return CGSize(width: cellWidth, height: cellWidth)
}