Question

我正在从xib中添加一个视图到我的ViewController中。然后我将其约束实际适合它

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    ...
    ...
    view!.addSubview(gamePreview)
    gamePreview.translatesAutoresizingMaskIntoConstraints = false
    if #available(iOS 9.0, *) {
        // Pin the leading edge of myView to the margin's leading edge
        gamePreview.leadingAnchor.constraintEqualToAnchor(view.leadingAnchor).active = true
        //Pin the trailing edge of myView to the margin's trailing edge
        gamePreview.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor).active = true

    } else {
        // Fallback on earlier versions
        view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .TrailingMargin, relatedBy: .Equal, toItem: view, attribute: .TrailingMargin, multiplier: 1, constant: 0))

        view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .LeadingMargin, relatedBy: .Equal, toItem: view, attribute: .LeadingMargin, multiplier: 1, constant: 0))
    }
    view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Top, relatedBy: .Equal, toItem: self.topLayoutGuide, attribute: .Bottom, multiplier: 1, constant: 0))
    view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute,multiplier: 1, constant: 131))
}

我正在尝试做什么：实际上适合我的视图将其限制在顶部，前导，跟踪到ViewController的视图，并使用前缀高度。我添加到主视图的视图有自己的透明背景视图，因此不需要边距（视图意味着设备的宽度大小，所以）。

我已经放置了2对线，这些线应该是相同的（在我的尝试中）和if，因为if中的前2行在iOS9中实际可用＆gt;只是，虽然我试图在else语句中为每个设备做同样的事情（从iOS 8开始）。

这就是我得到的：

iOS9 +左侧，iOS8 +右侧。透明背景被涂成红色以显示发生了什么（不要介意在图像中的不同高度，它们在app中的高度相等，而是在左右两侧查看增加的边距）

我也试过AutoLayoutDSL-Swift，但没有帮助，我不是专家，但每次尝试都只会让事情变得更糟。

如何使用经典的NSLayoutConstraints方法编写这些约束，以及如何使用AutoLayoutDSL或其分支框架以更好的方式编写所有约束？（或另一种选择，但现在大多数时候我都关注官方文库）

Answer 1

您需要使用leading和trailing属性，而不是leadingMargin和trailingMargin属性：

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    ...
    ...
    view!.addSubview(gamePreview)
    gamePreview.translatesAutoresizingMaskIntoConstraints = false

    view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Trailing, relatedBy: .Equal, toItem: view, attribute: .Trailing, multiplier: 1, constant: 0))            
    view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Leading, relatedBy: .Equal, toItem: view, attribute: .Leading, multiplier: 1, constant: 0))

    view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Top, relatedBy: .Equal, toItem: self.topLayoutGuide, attribute: .Bottom, multiplier: 1, constant: 0))
    view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute,multiplier: 1, constant: 131))
}

Answer 2

感谢@ Paulw11 ...这是解决方案

view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Trailing, relatedBy: .Equal, toItem: view, attribute: .Trailing, multiplier: 1, constant: 0))     
view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Leading, relatedBy: .Equal, toItem: view, attribute: .Leading, multiplier: 1, constant: 0))        
view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Top, relatedBy: .Equal, toItem: self.topLayoutGuide, attribute: .Bottom, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: gamePreview, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute,multiplier: 1, constant: 131))

此外，我设法重写它，因为它使用AutoLayoutDSL-Swift对任何感兴趣的人

view => gamePreview.trailing == view.trailing
     => gamePreview.leading == view.leading
     => gamePreview.height == 131
     => gamePreview.top == view.top + self.navigationController!.navigationBar.bounds.height + UIApplication.sharedApplication().statusBarFrame.size.height

最后一行有点长，因为view.top指的是真正的视图顶部，并没有考虑statusBar和navigationBar高度添加的填充。它们可以被替换为常数，等待有人提出更优雅的解决方案。

Answer 3

SWIFT 4更新

stackView.translatesAutoresizingMaskIntoConstraints = false

stackView.addConstraint(NSLayoutConstraint(item: stackView, attribute: .trailing, relatedBy: .equal, toItem: stackView, attribute: .trailing, multiplier: 1, constant: 0))
stackView.addConstraint(NSLayoutConstraint(item: stackView, attribute: .leading, relatedBy: .equal, toItem: stackView, attribute: .leading, multiplier: 1, constant: 0))

stackView.addConstraint(NSLayoutConstraint(item: stackView, attribute: .top, relatedBy: .equal, toItem: self.addLayoutGuide, attribute: .bottom, multiplier: 1, constant: 0))
stackView.addConstraint(NSLayoutConstraint(item: stackView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute,multiplier: 1, 
constant: 131))

Answer 4

为什么不使用约束激活？您可以这样做：

    var anchors = [NSLayoutConstraint]()
    anchors.append(view.topAnchor.constraint(equalTo: gamePreview.topAnchor, constant: 0))
    anchors.append(view.leadingAnchor.constraint(equalTo: gamePreview.leadingAnchor, constant: 0))
    anchors.append(view.trailingAnchor.constraint(equalTo: gamePreview.trailingAnchor, constant: 0))
    anchors.append(view.heightAnchor.constraint(equalTo: gamePreview.heightAnchor, multiplier: 1, constant: 131))
    NSLayoutConstraint.activate(anchors)

这是另一个。希望能帮助到你。您可以根据父/子交换view和gamePreview，也可以为约束创建通用的辅助扩展。我在YouTuber Here提供的教程中找到了一个，并对其进行了少许修改以接受开头/结尾，左右约束。您也可以在下面添加safeLayoutGuide，这使其面向未来。像这样：

    func anchor(_ top: UIView? = nil, left: UIView? = nil, bottom: UIView? = nil, right: UIView? = nil, width: UIView? = nil, height: UIView? = nil, topConstant: CGFloat = 0, leftConstant: CGFloat = 0, bottomConstant: CGFloat = 0, rightConstant: CGFloat = 0, widthConstant: CGFloat = 0, heightConstant: CGFloat = 0, isForLeading: Bool = false) -> [NSLayoutConstraint] {
    translatesAutoresizingMaskIntoConstraints = false

    var anchors = [NSLayoutConstraint]()
    if #available(iOS 11.0, *) {
        if let top = top {
            anchors.append(topAnchor.constraint(equalTo: top.safeAreaLayoutGuide.topAnchor, constant: topConstant))
        }

        if let left = left {
            if isForLeading  {
                anchors.append(leadingAnchor.constraint(equalTo: left.safeAreaLayoutGuide.leadingAnchor, constant: leftConstant))
            } else {
                anchors.append(leftAnchor.constraint(equalTo: left.safeAreaLayoutGuide.leftAnchor, constant: leftConstant))
            }
        }

        if let bottom = bottom {
            anchors.append(bottomAnchor.constraint(equalTo: bottom.safeAreaLayoutGuide.bottomAnchor, constant: -bottomConstant))
        }

        if let right = right {
            if isForLeading  {
                anchors.append(trailingAnchor.constraint(equalTo: right.safeAreaLayoutGuide.leadingAnchor, constant: rightConstant))
            } else {
                anchors.append(rightAnchor.constraint(equalTo: right.safeAreaLayoutGuide.rightAnchor, constant: -rightConstant))
            }
        }
        if let width = width {
            anchors.append(widthAnchor.constraint(equalTo: width.safeAreaLayoutGuide.widthAnchor, multiplier: 1, constant: widthConstant))
        } else if widthConstant > 0 {
            anchors.append(widthAnchor.constraint(equalToConstant: widthConstant))
        }

        if let height = height {
            anchors.append(heightAnchor.constraint(equalTo: height.safeAreaLayoutGuide.heightAnchor, multiplier: 1, constant: widthConstant))
        } else if heightConstant > 0 {
            anchors.append(widthAnchor.constraint(equalToConstant: heightConstant))
        }
        anchors.forEach({$0.isActive = true})
    } else {
        if let top = top {
            anchors.append(topAnchor.constraint(equalTo: top.topAnchor, constant: topConstant))
        }

        if let left = left {
            if isForLeading  {
                anchors.append(leadingAnchor.constraint(equalTo: left.leadingAnchor, constant: leftConstant))
            } else {
                anchors.append(leftAnchor.constraint(equalTo: left.leftAnchor, constant: leftConstant))
            }
        }

        if let bottom = bottom {
            anchors.append(bottomAnchor.constraint(equalTo: bottom.bottomAnchor, constant: -bottomConstant))
        }

        if let right = right {
            if isForLeading  {
                anchors.append(trailingAnchor.constraint(equalTo: right.leadingAnchor, constant: rightConstant))
            } else {
                anchors.append(rightAnchor.constraint(equalTo: right.rightAnchor, constant: -rightConstant))
            }
        }

        if let width = width {
            anchors.append(widthAnchor.constraint(equalTo: width.widthAnchor, multiplier: 1, constant: widthConstant))
        } else if widthConstant > 0 {
            anchors.append(widthAnchor.constraint(equalToConstant: widthConstant))
        }

        if let height = height {
            anchors.append(heightAnchor.constraint(equalTo: height.heightAnchor, multiplier: 1, constant: widthConstant))
        } else if heightConstant > 0 {
            anchors.append(widthAnchor.constraint(equalToConstant: heightConstant))
        }
        anchors.forEach({$0.isActive = true})
    }

    return anchors
}

然后这样称呼它：

        _ = view.anchor(gamePreview, left: gamePreview, right: gamePreview, height: gamePreview, heightConstant: 131, isForLeading: true)

Swift中的尾随和前导约束（NSLayoutConstraints）

4 个答案: