swift – 为什么没有调用UICollectionView insetForSectionsAtIndex？

概述我正在寻找使用以下功能,但不幸的是它没有被调用. func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewFlowLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets { l 我正在寻找使用以下功能,但不幸的是它没有被调用.

func collectionVIEw(collectionVIEw: UICollectionVIEw,layout collectionVIEwLayout: UICollectionVIEwFlowLayout,insetForSectionAtIndex section: Int) -> UIEdgeInsets {        let cellCount = Double(collectionVIEw.numberOfItems(inSection: section))        if let cell = collectionVIEw.cellForItem(at: IndexPath(row: 0,section: section))        {            let cellWIDth = Double(cell.frame.size.wIDth)            let totalCellWIDth = cellWIDth * cellCount            let cellSpacing = Double(collectionVIEwLayout.minimumInteritemSpacing)            let totalSpacingWIDth = cellSpacing * (cellCount - 1)            let leftInset = (collectionVIEw.frame.wIDth - CGfloat(totalCellWIDth + totalSpacingWIDth)) / 2            let rightInset = leftInset            return UIEdgeInsetsMake(0,leftInset,rightInset)        }    return collectionVIEw.layoutmargins}

我收到以下控制台错误,但我的单元格小于我的collectionVIEw,并且我将section insets和layout margin设置为0.

2017-03-30 11:25:14.624 Prep[92400:1862856] The behavior of the UICollectionVIEwFlowLayout is not defined because:
2017-03-30 11:25:14.624 Prep[92400:1862856] the item height must be less than the height of the UICollectionVIEw minus the section insets top and bottom values,minus the content insets top and bottom values.
2017-03-30 11:25:14.624 Prep[92400:1862856] The relevant UICollectionVIEwFlowLayout instance is,and it is attached to ; layer = ; contentOffset: {0,0}; contentSize: {0,68.5}> collection vIEw layout: .
2017-03-30 11:25:14.625 Prep[92400:1862856] Make a symbolic breakpoint at UICollectionVIEwFlowLayoutBreakForInvalIDSizes to catch this in the deBUGger.
cell height –> 42.0

协议

class OvervIEwVIEwController: UIVIEwController,UICollectionVIEwDelegate,UICollectionVIEwDataSource,UICollectionVIEwDelegateFlowLayout {@IBOutlet weak var vipCollectionVIEw: UICollectionVIEw!var hostedMeetingsArray: [String]?var vipArray: [Attendee]?class OvervIEwVIEwController: UIVIEwController,UICollectionVIEwDelegateFlowLayout {@IBOutlet weak var vipCollectionVIEw: UICollectionVIEw!var hostedMeetingsArray: [String]?var vipArray: [Attendee]?

解决方法 好吧,没有调用insetForSectionAt的问题是你必须像这样实现它：

func collectionVIEw(_ collectionVIEw: UICollectionVIEw,layout collectionVIEwLayout: UICollectionVIEwLayout,insetForSectionAt section: Int) -> UIEdgeInsets {   //access to minimumInteritemSpacing by casting to UICollectionVIEwFlowLayout   let layout = collectionVIEwLayout as! UICollectionVIEwFlowLayout   let spacing = layout.minimumInteritemSpacing          return UIEdgeInsetsMake(0.5,0.5,0)}

看看UICollectionVIEwDelegateFlowLayout协议. insetForSectionAt声明如下：

@available(iOS 6.0,*)optional public func collectionVIEw(_ collectionVIEw: UICollectionVIEw,insetForSectionAt section: Int) -> UIEdgeInsets

所以你需要第一个可选参数来实现这个功能.

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