NSLayoutConstraint可以將視圖固定到superview的下邊緣

Question

一個可重復的例子

class ViewController: UIViewController {

   var created = false

   override func viewDidLayoutSubviews() {
      super.viewDidLayoutSubviews()
      if !created {

         let scrollView = UIScrollView()
         scrollView.backgroundColor = UIColor.grayColor()
         view.addSubview(scrollView)

         let kidView = UIView()
         kidView.backgroundColor = UIColor.redColor()
         kidView.translatesAutoresizingMaskIntoConstraints = false

         scrollView.addSubview(kidView)

         scrollView.translatesAutoresizingMaskIntoConstraints = false
         kidView.translatesAutoresizingMaskIntoConstraints = false

         view.addConstraints(
            NSLayoutConstraint.constraintsWithVisualFormat("H:|[scrollView]|", options: .AlignAllLeft, metrics: nil, views: ["scrollView": scrollView])
         )
         view.addConstraints(
            NSLayoutConstraint.constraintsWithVisualFormat("V:|[scrollView]|", options: .AlignAllLeft, metrics: nil, views: ["scrollView": scrollView])
         )

         kidView.addConstraints([
            NSLayoutConstraint(item: kidView, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 100),
            NSLayoutConstraint(item: kidView, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 100),
         ])

         scrollView.addConstraints([
            NSLayoutConstraint(item: kidView, attribute: .CenterX, relatedBy: .Equal, toItem: scrollView, attribute: .CenterX, multiplier: 1, constant: 0),
            NSLayoutConstraint(item: kidView, attribute: .Bottom, relatedBy: .Equal, toItem: scrollView, attribute: .Bottom, multiplier: 1, constant: 0),
//            NSLayoutConstraint(item: kidView, attribute: .CenterY, relatedBy: .Equal, toItem: scrollView, attribute: .CenterY, multiplier: 1, constant: 0),
         ])

         created = true
      }
   }

}

問題

我想將我的自定義視圖對齊到我的UIScrollView的底部邊緣，但我似乎只能將它與頂部或垂直中心對齊。

scrollView.addConstraints([
    NSLayoutConstraint(
        item: circleContainerView, 
        attribute: .Top, 
        relatedBy: .Equal, 
        toItem: scrollView, 
        attribute: .Top, 
        multiplier: 1, 
        constant: 0),
])

scrollView.addConstraints([
    NSLayoutConstraint(
        item: circleContainerView, 
        attribute: .CenterY, 
        relatedBy: .Equal, 
        toItem: scrollView, 
        attribute: .CenterY, 
        multiplier: 1, 
        constant: 0),
])

但我想要的是擁有這樣的照片。 我如何到達那里？

Answer 1

具有自動布局的ScrollView的工作方式不同，您可以通過設置translatesAutoresizingMaskIntoConstraints = true並顯式設置contentSize來僅使用一個子視圖。 或者你設置translatesAutoresizingMaskIntoConstraints = false並讓它找出它自己的約束。

在您的情況下，您可以在滾動內添加一個不可見的視圖並將其固定到頂部並將其高度設置為scrollView.bounds.size.height然后使用該不可見視圖設置創建約束

像這樣改變你的約束

scrollView.addConstraints([
    NSLayoutConstraint(
        item: circleContainerView, 
        attribute: .Bottom, 
        relatedBy: .Equal, 
        toItem: invisibleView, 
        attribute: .Bottom, 
        multiplier: 1, 
        constant: 0),
])

有關更多詳細信息，請訪問此鏈接 ，閱讀純自動布局方法

更新：修改后的代碼

class ViewController: UIViewController {

    var created = false

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        if !created {

            let scrollView = UIScrollView()
            scrollView.backgroundColor = UIColor.grayColor()
            view.addSubview(scrollView)

            let kidView = UIView()
            kidView.backgroundColor = UIColor.redColor()

            scrollView.addSubview(kidView)

            scrollView.translatesAutoresizingMaskIntoConstraints = false
            kidView.translatesAutoresizingMaskIntoConstraints = false

            scrollView.frame = view.bounds;
            scrollView.contentSize = view.bounds.size

            // Add an invisible view

            let inV = UIView()
            inV.backgroundColor = UIColor.clearColor()
            inV.translatesAutoresizingMaskIntoConstraints = false
            scrollView.addSubview(inV)


            view.addConstraints(
                NSLayoutConstraint.constraintsWithVisualFormat("H:|[scrollView]|", options: .AlignAllLeft, metrics: nil, views: ["scrollView": scrollView])
            )
            view.addConstraints(
                NSLayoutConstraint.constraintsWithVisualFormat("V:|[scrollView]|", options: .AlignAllLeft, metrics: nil, views: ["scrollView": scrollView])
            )

            var constraint = NSLayoutConstraint(item: inV, attribute: .Top, relatedBy: .Equal, toItem: scrollView, attribute: .Top, multiplier: 1, constant: 0)

            view.addConstraint(constraint)

            constraint = NSLayoutConstraint(item: inV, attribute: .Left, relatedBy: .Equal, toItem: scrollView, attribute: .Left, multiplier: 1, constant: 0)
            view.addConstraint(constraint)

            inV.addConstraints([
                NSLayoutConstraint(item: inV, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .Width, multiplier: 1, constant: 10),
                NSLayoutConstraint(item: inV, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .Height, multiplier: 1, constant: self.view.bounds.size.height),
                ])

            //

            kidView.addConstraints([
                NSLayoutConstraint(item: kidView, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .Width, multiplier: 1, constant: 100),
                NSLayoutConstraint(item: kidView, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .Height, multiplier: 1, constant: 100),
                ])

            view.addConstraints([
                NSLayoutConstraint(item: kidView, attribute: .CenterX, relatedBy: .Equal, toItem: scrollView, attribute: .CenterX, multiplier: 1, constant: 0),
                NSLayoutConstraint(item: kidView, attribute: .Bottom, relatedBy: .Equal, toItem: inV, attribute: .Bottom, multiplier: 1, constant: 0),
                ])

            created = true
        }
    }

}