func addConstraintsWithFormat(format: String,views: UIView...) {
   var viewsDictionary = [String: UIView]()
   for (index,view) in views.enumerate() {
      let key = "v\(index)"
      viewsDictionary[key] = view
      view.translatesAutoresizingMaskIntoConstraints = false
   }
   addConstraints(NSLayoutConstraint.constraintsWithVisualFormat(format,options: NSLayoutFormatOptions(),metrics: nil,views: viewsDictionary))
}

有趣的是,在我的UICollectionView中,我将一个SubView添加到单个单元格,并将背景颜色设置为白色.当我注释掉设置子视图背景的行时,背景是白色的,当我取消注释为子视图设置视觉格式的约束的行时,不设置背景颜色.

这是两条相互交错的线路：

func chronicleOneClicked(sender: UIButton) {
   point1view.backgroundColor = UIColor.whiteColor()

   addSubview(point1view)
   //When the below is commented the background of point1view disappears   
   //addConstraintsWithFormat("|-50-[v0]-50-|",views: point1view)
}

当我打印(子视图)我看到,具有白色背景颜色的UIView是视图堆栈(堆栈顶部)中最高的.当我打印出subviews [subviews.count-1] .backgroundColor我得到可选(UIDeviceWhiteColorSpace 1 1)这是我期望的.这是奇怪的,因为颜色不显示.

我不知道如何看待幕后发生的事情,以确认在后一种情况下背景是被设定的.

这一切都发生在UiCollectionViewCell的一个类中,我正在使用它作为我的UICollectionView单元格的类,可以在这里完整地查看：

https://gist.github.com/ebbnormal/edb79a15dab4797946e0d1f6905c2dd0

这是两种情况下的屏幕截图,第一种情况是将addConstraintsWithFormat的行注释掉,第二种情况是取消注释的位置：在第一种情况下,point1subview的子视图以白色背景突出显示.

这是我如何设置视图.这一切都发生在覆盖UICollectionViewCell的类中

class myClass : UICollectionViewCell {
   var chronicle: BrowsableChronicle? {
      didSet{
         //etc.
         point1.addTarget(self,action: #selector(chronicleOneClicked(_:)),forControlEvents: UIControlEvents.TouchUpInside)
      }
   }

   override init(frame: CGRect) {
      super.init(frame: frame)
      setupViews()
   }

   let point1 : PointButtonView = {
      let pointView = PointButtonView(frame: CGRectMake(0,25,25 ))
      return pointView
   }()
   //NOTE here is where I create the view,whose background doesn't display
   let point1view : UIView = {
      let pointView = UIView(frame: CGRectMake( 0,200,270))
      pointView.backgroundColor = UIColor.whiteColor()
      let title = UILabel(frame: CGRectMake(0,21))
      title.font = UIFont(name:"HelveticaNeue-Bold",size: 16.0)

      pointView.addSubview(title)
      let summary = UILabel(frame: CGRectMake(0,190,260))
      summary.lineBreakMode = NSLineBreakMode.ByWordWrapping
      summary.numberOfLines = 4
      summary.font = UIFont(name:"HelveticaNeue",size: 12.5)
      pointView.addSubview(summary)

      let button = UIButton(frame: CGRectMake(0,30))
      button.backgroundColor = UIColor(red:0.00,green:0.90,blue:0.93,alpha:1.0)
      pointView.addSubview(button)

      pointView.tag = 100

      return pointView
   }()

   //NOTE: here is where I add the subview to the UICollectionViewCell view
   func chronicleOneClicked(sender: UIButton){
      addSubview(point1view)
      addConstraintsWithFormat("H:|-20-[v0]-20-|",views: point1view)
      //TODO anytime i add a constraint here the background color leaves!
      print(subviews[subviews.count-1].backgroundColor) //Prints white
   }
}

更新：我认为也许这是与这个问题有关：

UITableViewCell subview disappears when cell is selected

在哪里选择了UICollectionViewCell,因此iOS会自动将backgroundColor设置为清除.问题是,我实现了UIView的这个类扩展,以查看在setColor上调用了setSet,当它设置为clear时,我将其设置为白色.但是,当我首先设置视图的颜色时,它只会在backgroundColor上调用didSet.这是我用来覆盖UIView类的代码：

class NeverClearView: UIView {
   override var backgroundColor: UIColor? {
      didSet {
         print("background color is being set")
         if backgroundColor == UIColor.clearColor() {
            print("set to a clear color")
            backgroundColor = UIColor.whiteColor()
         }
      }
   }
}