Question

我有3个UIView图层的蛋糕，具有编程约束。

用于以编程方式设置约束的构造函数：

func setupViewConstraints(item:UIView, leadingTo:NSLayoutXAxisAnchor, leadingCon:CGFloat, 
trailingTo:NSLayoutXAxisAnchor, trailingCon:CGFloat, topTo:NSLayoutYAxisAnchor, 
topCon:CGFloat, bottomTo:NSLayoutYAxisAnchor, bottomCon:CGFloat) {
    item.translatesAutoresizingMaskIntoConstraints = false
    item.leadingAnchor.constraint(equalTo: leadingTo, constant: leadingCon).isActive = true
    item.trailingAnchor.constraint(equalTo: trailingTo, constant: trailingCon).isActive = true
    item.topAnchor.constraint(equalTo: topTo, constant:topCon).isActive = true
    item.bottomAnchor.constraint(equalTo: bottomTo, constant:bottomCon).isActive = true
}

最低的基础层是lightGray。

view = UIView()
view.backgroundColor = .lightGray

第二层包含2个带有约束的UIView（红色和蓝色）。

let red = UIView()
red.backgroundColor = .red
view.addSubview(red)
setupViewConstraints(item: red, leadingTo: view.leadingAnchor, leadingCon: 0, trailingTo: view.trailingAnchor, trailingCon: -(view.frame.width)*0.2), topTo: view.topAnchor, topCon: 0, bottomTo: view.bottomAnchor, bottomCon: -(view.frame.width)*0.8)

let blue = UIView()
blue.backgroundColor = .blue
view.addSubview(blue)
setupViewConstraints(item: blue, leadingTo: view.leadingAnchor, leadingCon: 0, trailingTo: view.trailingAnchor, trailingCon: -(view.frame.width)*0.2), topTo: red.bottomAnchor, topCon: 0, bottomTo: view.bottomAnchor, bottomCon: 0)

在顶部我有黄色UIView层，它与所有较低层重叠。

let yellow = UIView()
yellow.backgroundColor = .yellow
view.addSubview(yellow)
setupViewConstraints(item: yellow, leadingTo: view.leadingAnchor, leadingCon: 0, trailingTo: view.trailingAnchor, trailingCon: 0, topTo: view.topAnchor, topCon: 0, bottomTo: view.bottomAnchor, bottomCon: 0)

此外，我在黄色UINavigationBar内有UINavigationItem UIView。

//Add navigation item and buttons
        naviItem = UINavigationItem()
        naviItem.setRightBarButton(UIBarButtonItem(barButtonSystemItem:.add, target:self, action:#selector(goToDestVC)), animated: true)
        naviItem.setLeftBarButton(UIBarButtonItem(image: UIImage(named: "hamburger_slim_30"), style: .plain, target: self, action: #selector(hamburgerBtnPressed)), animated: true)

        //Add navigation bar with transparent background
        naviBar = UINavigationBar()
        naviBar.setBackgroundImage(UIImage(), for: .default)
        naviBar.shadowImage = UIImage()
        naviBar.isTranslucent = true

// Assign the navigation item to the navigation bar
        naviBar.items = [naviItem]

        view.addSubview(naviBar)
        setupViewConstraints(item: naviBar, leadingTo: yellow.leadingAnchor, leadingCon: 0, trailingTo: yellow.trailingAnchor, trailingCon: 0, topTo: yellow.topAnchor, topCon: 0, bottomTo: yellow.bottomAnchor, bottomCon: -(view.frame.height)*0.9))

我有hamburgerBtnPressed函数，它应该将黄色图层向右移动80％（我将前导和尾随常量的值改为80％），但这不起作用!! ！

var hamburgerMenuIsVisible = false

    @objc func hamburgerBtnPressed(_ sender: Any) {

        if !hamburgerMenuIsVisible {

            let menuWidth = (self.view.frame.width)*0.8

              setupViewConstraints(item: layoutView, leadingTo: view.leadingAnchor, leadingCon: menuWidth, trailingTo: view.trailingAnchor, trailingCon: menuWidth, topTo: view.topAnchor, topCon: 0, bottomTo: view.bottomAnchor, bottomCon: 0)

            hamburgerMenuIsVisible = true

        } else {

            setupViewConstraints(item: layoutView, leadingTo: view.leadingAnchor, leadingCon: 0, trailingTo: view.trailingAnchor, trailingCon: 0, topTo: view.topAnchor, topCon: 0, bottomTo: view.bottomAnchor, bottomCon: 0)

            hamburgerMenuIsVisible = false
        }

        // layoutIfNeeded() lays out the subviews immediately and forces the layout before drawing
        UIView.animate(withDuration: 0.2, delay:0.0, options: .curveEaseIn, animations: {

            self.view.layoutIfNeeded()

        }) { (animationComplete) in
            print("Animation is complete!")
        }
    }

但如果我将前导和尾随常量的值更改为负数，一切都会起作用，菜单会向左移动而没有任何问题。

let menuWidth = -(self.view.frame.width)*0.8

请解释一下......问题是什么？为什么黄色UIView向左移动了约束的负值，并且不能与约束的正值一起使用？并给出错误：

Probably at least one of the constraints in the following list is one you don't want. 
(
    "<NSLayoutConstraint:0x6040002853c0 UIView:0x7fa947c35850.trailing == UIView:0x7fa947e1d2d0.trailing   (active)>",
    "<NSLayoutConstraint:0x604000092750 UIView:0x7fa947c35850.trailing == UIView:0x7fa947e1d2d0.trailing + 331.2   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x604000092750 UIView:0x7fa947c35850.trailing == UIView:0x7fa947e1d2d0.trailing + 331.2   (active)>

更新：我选择选项2 ：保持对要更改的约束的引用，并调整其常量。在layoutIfNeeded之前也需要调用setNeedsLayout。

更新的代码：

var leadingC: NSLayoutConstraint!
var trailingC: NSLayoutConstraint!
var yellow: UIView!

的loadView（）：

    yellow = UIView()
        yellow.backgroundColor = .yellow
        view.addSubview(yellow)

        //Set up leading and trailing constraints for handling yellow view shift
        leadingC = yellow.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0)
        trailingC = yellow.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0)

//Put leadingC.constant and trailingC.constant into the function
        setupViewConstraints(item: yellow, leadingTo: view.leadingAnchor, leadingCon: leadingC!.constant, trailingTo: view.trailingAnchor, trailingCon: trailingC.constant, topTo: view.topAnchor, topCon: 0, bottomTo: view.bottomAnchor, bottomCon: 0)

更新了汉堡功能：

 @objc func hamburgerBtnPressed(_ sender: Any) {

        if !hamburgerMenuIsVisible {

            let menuWidth = (self.view.frame.width)*0.8


            leadingC!.constant = menuWidth
            trailingC!.constant = menuWidth

            print(leadingC.constant, trailingC.constant)

            hamburgerMenuIsVisible = true

        } else {

            leadingC!.constant = 0
            trailingC!.constant = 0


            hamburgerMenuIsVisible = false
        }

        // layoutIfNeeded() lays out the subviews immediately and forces the layout before drawing
        UIView.animate(withDuration: 0.2, delay:0.0, options: .curveEaseIn, animations: {

            self.view.setNeedsLayout()
            self.view.layoutIfNeeded()

        }) { (animationComplete) in
            print("Animation is complete!")
        }
    }
    var hamburgerMenuIsVisible = false

我没有错误，＆＃34;动画完成！＆＃34;也打印过，但屏幕上没有任何反应，没有动画。

Answer 1

首先，它需要负值，因为需要在正确的方向上设置约束。更改此设置，您可以删除所有这些负常量：

 //myDbBinary
 let
Source = Binary.Buffer(File.Contents(DataFolder_param & FileName_param),  
 [CreateNavigationProperties=true]))
in
 Source

 // Table1 Query
 let
Source = Access.Database(myDbBinary, [CreateNavigationProperties=true]),
_Table1 = Source{[Schema="",Item="Table1"]}[Data]
 in
_Table1

到

item.leadingAnchor.constraint(equalTo: leadingTo, constant: leadingCon).isActive = true
item.trailingAnchor.constraint(equalTo: trailingTo, constant: trailingCon).isActive = true
item.topAnchor.constraint(equalTo: topTo, constant:topCon).isActive = true
item.bottomAnchor.constraint(equalTo: bottomTo, constant:bottomCon).isActive = true

其次，每次调用item.leadingAnchor.constraint(equalTo: leadingTo, constant: leadingCon).isActive = true trailingTo.constraint(equalTo: item.trailingAnchor, constant: trailingCon).isActive = true item.topAnchor.constraint(equalTo: topTo, constant:topCon).isActive = true bottomTo.constraint(equalTo: item.bottomAnchor, constant:bottomCon).isActive = true时，您都在创建并激活另一组约束。

选项1：

在重新设置之前删除黄色视图的所有约束。

选项2：

保持对要更改的约束的引用，并调整其常量。您可能需要在setupViewConstraints之前致电setNeedsLayout。

选项3：

添加2个约束。最初的主要约束，以及您想要的宽度。当您要显示/隐藏菜单时，将第一个约束的优先级更改为layoutIfNeeded（默认为999）并切换另一个约束的1000属性。

isActive

选项2可能是性能最佳的选项。来自apple docs：

在现有约束上设置常量会更好而不是删除约束并添加一个新的约束旧的除了它有不同的常数

以编程方式超出UIView约束

1 个答案: