Ios 如何确定；阴影的z指数；

我为标题感到抱歉，无法综合该问题。问题是：

在我的UICollectionView中，有一些单元格想要放置阴影，它们彼此排列得非常近，这使得每个单元格的阴影都到达相邻单元格（第一个图像），而我想要的是，它只到达背景（第二个图像）

我的想法或尝试：

我无法将视图放在单元格后面，向其添加帧，并在此视图中应用阴影，因为单元格具有动态移动（UIDynamics CollectionView布局）

我尝试在UICollectionViewLayout的子类中，将所有这些单元格放在同一个z索引中。不起作用。找出原因：

（…）具有相同值的项具有未确定的 秩序

---

请帮我解决我的问题。谢谢

您可以尝试将阴影定义为补充视图，与各自的单元格对齐，并为其提供比单元格更低的z顺序。

您可以尝试将阴影定义为补充视图，与各自的单元格对齐，并为其提供比单元格更低的z顺序。

从TheEye响应中，我决定实现ui装饰视图。现在一切都很好

// MARK: At UICollectionViewCustomLayout:

public override init() {
    super.init()
    // Register the NIB of the view that will hold the shadows:
    let nib = UINib(nibName: "Shadow", bundle: nil)
    self.registerNib(nib, forDecorationViewOfKind: "shadow")
}

public override func layoutAttributesForDecorationViewOfKind(elementKind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
    let layoutAtt: UICollectionViewLayoutAttributes = UICollectionViewLayoutAttributes(forDecorationViewOfKind: "shadow", withIndexPath: indexPath)
    layoutAtt.frame = (layoutAttributesForItemAtIndexPath(indexPath)?.frame)!
    layoutAtt.zIndex = -1
    return layoutAtt
    }

public override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    var atts = [UICollectionViewLayoutAttributes]()
    let numberOfItems:Int = (self.collectionView?.numberOfItemsInSection(0))!
    for index in 0..<numberOfItems {
        let layoutItem = layoutAttributesForItemAtIndexPath(NSIndexPath(forItem: index, inSection: 0))!
        let frameItem = layoutItem.frame
        if CGRectIntersectsRect(frameItem, rect) {
            atts.append(layoutAttributesForDecorationViewOfKind("shadow", atIndexPath: NSIndexPath(forItem: index, inSection: 0))!)
            atts.append(layoutItem)
        }
    }
    return atts
}

// MARK: At the Nib Class File:

// Here I created a additional view to append the shadow. 
// Thats because awakeFromNib() is called before the UICollectionViewCustomLayout 
// have a chance to layout it, but I want to make 
// use of shadowPath to gain performance, thats why 
// I make use of the additional UIView with autolayout stuffs.

@IBOutlet weak var shadowView: UIView!

override func awakeFromNib() {
    super.awakeFromNib()
    shadowView.layer.shadowOffset = CGSizeMake(0, 0)
    shadowView.layer.shadowColor = UIColor.yellowColor().CGColor
    shadowView.layer.shadowRadius = 3
    shadowView.layer.shadowOpacity = 1
    let shadowFrame: CGRect = shadowView.layer.bounds
    let shadowPath: CGPathRef = UIBezierPath(rect: shadowFrame).CGPath
    shadowView.layer.shadowPath = shadowPath
    shadowView.clipsToBounds = false
    self.clipsToBounds = false
}

//标记：在UICollectionViewCustomLayout:
公共重写init（）{
super.init（）
//注册将容纳阴影的视图笔尖：
设nib=UINib（nibName:“Shadow”，bundle:nil）
self.registerNib（nib，用于类的生态视图：“影子”）
}
public override func LayoutAttribute ForDecorationViewOfKind（elementKind:String，atIndexPath indexPath:NSIndexPath）->UICollectionViewLayoutAttribute？{
让layoutAtt:UICollectionViewLayoutAttributes=UICollectionViewLayoutAttributes（对于类别为“shadow”的ecorationViewOfKind，带indexPath:indexPath）
layoutAtt.frame=（layoutatributesforItemAtIndexPath（indexPath）？.frame）！
layoutAtt.zIndex=-1
返回layoutAtt
}
公共覆盖函数layoutAttributesForElementsInRect（rect:CGRect）->[UICollectionViewLayoutAttributes]？{
var atts=[UICollectionViewLayoutAttribute]（）
让numberOfItems:Int=（self.collectionView？.numberOfItemsInSection（0））！
对于0中的索引，从TheEye响应中，我决定实现
UIDecorationViews
。现在一切都很好

// MARK: At UICollectionViewCustomLayout:

public override init() {
    super.init()
    // Register the NIB of the view that will hold the shadows:
    let nib = UINib(nibName: "Shadow", bundle: nil)
    self.registerNib(nib, forDecorationViewOfKind: "shadow")
}

public override func layoutAttributesForDecorationViewOfKind(elementKind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
    let layoutAtt: UICollectionViewLayoutAttributes = UICollectionViewLayoutAttributes(forDecorationViewOfKind: "shadow", withIndexPath: indexPath)
    layoutAtt.frame = (layoutAttributesForItemAtIndexPath(indexPath)?.frame)!
    layoutAtt.zIndex = -1
    return layoutAtt
    }

public override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    var atts = [UICollectionViewLayoutAttributes]()
    let numberOfItems:Int = (self.collectionView?.numberOfItemsInSection(0))!
    for index in 0..<numberOfItems {
        let layoutItem = layoutAttributesForItemAtIndexPath(NSIndexPath(forItem: index, inSection: 0))!
        let frameItem = layoutItem.frame
        if CGRectIntersectsRect(frameItem, rect) {
            atts.append(layoutAttributesForDecorationViewOfKind("shadow", atIndexPath: NSIndexPath(forItem: index, inSection: 0))!)
            atts.append(layoutItem)
        }
    }
    return atts
}

// MARK: At the Nib Class File:

// Here I created a additional view to append the shadow. 
// Thats because awakeFromNib() is called before the UICollectionViewCustomLayout 
// have a chance to layout it, but I want to make 
// use of shadowPath to gain performance, thats why 
// I make use of the additional UIView with autolayout stuffs.

@IBOutlet weak var shadowView: UIView!

override func awakeFromNib() {
    super.awakeFromNib()
    shadowView.layer.shadowOffset = CGSizeMake(0, 0)
    shadowView.layer.shadowColor = UIColor.yellowColor().CGColor
    shadowView.layer.shadowRadius = 3
    shadowView.layer.shadowOpacity = 1
    let shadowFrame: CGRect = shadowView.layer.bounds
    let shadowPath: CGPathRef = UIBezierPath(rect: shadowFrame).CGPath
    shadowView.layer.shadowPath = shadowPath
    shadowView.clipsToBounds = false
    self.clipsToBounds = false
}

//标记：在UICollectionViewCustomLayout:
公共重写init（）{
super.init（）
//注册将容纳阴影的视图笔尖：
设nib=UINib（nibName:“Shadow”，bundle:nil）
self.registerNib（nib，用于类的生态视图：“影子”）
}
public override func LayoutAttribute ForDecorationViewOfKind（elementKind:String，atIndexPath indexPath:NSIndexPath）->UICollectionViewLayoutAttribute{
让layoutAtt:UICollectionViewLayoutAttributes=UICollectionViewLayoutAttributes（对于类别为“shadow”的ecorationViewOfKind，带indexPath:indexPath）
layoutAtt.frame=（layoutatributesforItemAtIndexPath（indexPath）？.frame）！
layoutAtt.zIndex=-1
返回layoutAtt
}
公共覆盖函数layoutAttributesForElementsInRect（rect:CGRect）->[UICollectionViewLayoutAttributes]{
var atts=[UICollectionViewLayoutAttribute]（）
让numberOfItems:Int=（self.collectionView？.numberOfItemsInSection（0））！
对于0中的索引，做得很好-但我会更改
layouttributesforementsinrect
函数，以检查装饰视图的类型，并返回“阴影”的阴影类型-它更通用，并且在添加更多装饰视图时也能工作。做得好-但是我会更改
layouttributesforementsinrect
函数以检查装饰视图的类型并返回“shadow”类型的阴影-它更通用，并且在添加更多装饰视图时也能工作。