UICollectionView自定义流布局在滚动时崩溃 [英] UICollectionView custom flow layout crashes on scrolling
问题描述
我正在创建带有节标题的自定义flowLayout.
I am creating a custom flowLayout with section headers.
这是我的flowLayout.swift
here is my flowLayout.swift
import UIKit
class FlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
// let attributesForElementsInRect = super.
var newAttributesForElementsInRect = [UICollectionViewLayoutAttributes]()
// unwrap super's attributes
guard let attributesForElementsInRect = super.layoutAttributesForElementsInRect(rect) else { return nil }
// modify attributes
var leftMargin: CGFloat = 0.0;
for attributes in attributesForElementsInRect {
let itemAttributesCopy = attributes.copy() as! UICollectionViewLayoutAttributes
if( itemAttributesCopy.frame.size.width + leftMargin > self.collectionView?.frame.size.width)
{
leftMargin = 8.0
}
if (itemAttributesCopy.frame.origin.x == self.sectionInset.left) {
leftMargin = self.sectionInset.left
} else {
var newLeftAlignedFrame = itemAttributesCopy.frame
newLeftAlignedFrame.origin.x = leftMargin
itemAttributesCopy.frame = newLeftAlignedFrame
}
leftMargin += itemAttributesCopy.frame.size.width + 8
print(itemAttributesCopy.frame)
newAttributesForElementsInRect.append(itemAttributesCopy)
print(itemAttributesCopy)
}
return newAttributesForElementsInRect
}
}
这是我的ViewController,具有节标题的委托功能
here is my ViewController with delegate function for section header
func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
if(sectionsArray.count == 0)
{
return 1
}
else
{
return sectionsArray.count
}
}
func collectionView(collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionReusableView {
let headerView: TagHeader = collectionView.dequeueReusableSupplementaryViewOfKind(kind, withReuseIdentifier: "TagHeader", forIndexPath: indexPath) as! TagHeader
headerView.sectionLabel.text = sectionsArray[indexPath.section].header
return headerView
}
因此,当我运行该应用程序时,它会向我显示节标题,并且一切正常.
So when I run the app, it shows me the section headers and everything works fine.
但是当我滚动时,应用程序崩溃,并出现调试器以下错误
But when I scroll, app crashes with following error from debugger
2016-07-01 18:52:12.051 TagFlowLayout[15025:4704387] *** Assertion failure in -[UICollectionViewData validateLayoutInRect:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3512.60.7/UICollectionViewData.m:408
2016-07-01 18:52:12.054 TagFlowLayout[15025:4704387] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'layout attributes for supplementary item at index path (<NSIndexPath: 0x17e96f70> {length = 2, path = 0 - 0}) changed from <UICollectionViewLayoutAttributes: 0x17e7ab00> index path: (<NSIndexPath: 0x17d8fb30> {length = 2, path = 0 - 0}); element kind: (UICollectionElementKindSectionHeader); frame = (8 0; 314 50); zIndex = 10; to <UICollectionViewLayoutAttributes: 0x17e9d770> index path: (<NSIndexPath: 0x17e96f70> {length = 2, path = 0 - 0}); element kind: (UICollectionElementKindSectionHeader); frame = (0 0; 314 50); zIndex = 10; without invalidating the layout'
推荐答案
在更新之前,您需要使现有布局无效,请参见错误消息的结尾:
You need to invalidate the existing layout before updating, see the end of the error message:
在不使布局无效的情况下
without invalidating the layout
您应该重写UICollectionViewFlowLayout子类中的方法:
You should override the method at the subclass of UICollectionViewFlowLayout:
override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
return true
}
有关更多参考,请参见 UICollectionViewLayout的Apple文档
For more reference see Apple Documentation for UICollectionViewLayout
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