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, 0, 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, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
@IBOutlet weak var vipCollectionView: UICollectionView!
var hostedMeetingsArray: [String]?
var vipArray: [Attendee]?
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(0.5,0,0.5,0)
}
看看UICollectionViewDelegateFlowLayout协议. insetForSectionAt声明如下：
@available(iOS 6.0, *) optional public func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets
所以你需要第一个可选参数来实现这个功能.