AutoLayout约束以适应矩形内的视图，保持一定的纵横比（以编程方式）

Posted 2023-03-15

【中文标题】AutoLayout约束以适应矩形内的视图，保持一定的纵横比（以编程方式）

【英文标题】：AutoLayout constraints to fit view inside rectangle, preserving a certain aspect ratio (programmatically)

【发布时间】：2018-03-16 15:12:25

【问题描述】：

我想将图像放入一个应该具有特定纵横比的矩形内。不管它是什么，它都应该找到一个适合矩形的形式。我在故事板中玩耍并得到了这个：

虚线边框的优先级较低（250）。 这在故事板中有效。但是，我需要以编程方式创建这些约束，所以我这样尝试（我使用的是SnapKit，它只是提供了更好的AutoLayout 语法。它应该是不言自明的）：

let topView = UIView()
topView.translatesAutoresizingMaskIntoConstraints = false
topView.backgroundColor = .gray
view.addSubview(topView)

topView.snp.makeConstraints  (make) in
        make.top.equalToSuperview()
        make.left.equalToSuperview()
        make.trailing.equalToSuperview()
        make.height.equalTo(250)
        

// This view should have a specific aspect ratio and fit inside topView
let holderView = UIView()
holderView.translatesAutoresizingMaskIntoConstraints = false
holderView.backgroundColor = .red
topView.addSubview(holderView)

holderView.snp.makeConstraints  (make) in
        make.center.equalToSuperview() // If I remove this one, there's no auto-layout issue, but then it's offset
        make.edges.equalToSuperview().priority(250) // sets leading, trailing, top and bottom
        make.edges.greaterThanOrEqualToSuperview().priority(1000)
        make.width.equalTo(holderView.snp.height).multipliedBy(3/2)
        

如果您将其粘贴到一个空的 ViewController 中并启动它，您会遇到以下问题：

2018-03-16 15:38:50.188867+0100 DemoProject[11298:850932] [LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. 
Try this: 
    (1) look at each constraint and try to figure out which you don't expect; 
    (2) find the code that added the unwanted constraint or constraints and fix it. 

"<SnapKit.LayoutConstraint:[e-mail]#24 UIView:0x7fcd82d12440.left == UIView:0x7fcd82d12640.left>",
"<SnapKit.LayoutConstraint:[e-mail]#25 UIView:0x7fcd82d12440.trailing == UIView:0x7fcd82d12640.trailing>",
"<SnapKit.LayoutConstraint:[e-mail]#26 UIView:0x7fcd82d12440.height == 250.0>",
"<SnapKit.LayoutConstraint:[e-mail]#35 UIView:0x7fcd8580dad0.centerX == UIView:0x7fcd82d12440.centerX>",
"<SnapKit.LayoutConstraint:[e-mail]#35 UIView:0x7fcd8580dad0.centerY == UIView:0x7fcd82d12440.centerY>",
"<SnapKit.LayoutConstraint:[e-mail]#37 UIView:0x7fcd8580dad0.top >= UIView:0x7fcd82d12440.top>",
"<SnapKit.LayoutConstraint:[e-mail]#37 UIView:0x7fcd8580dad0.right >= UIView:0x7fcd82d12440.right>",
"<SnapKit.LayoutConstraint:[e-mail]#38 UIView:0x7fcd8580dad0.width == UIView:0x7fcd8580dad0.height>",
"<NSLayoutConstraint:0x600000092cf0 'UIView-Encapsulated-Layout-Width' UIView:0x7fcd82d12640.width == 414   (active)>"


Will attempt to recover by breaking constraint <SnapKit.LayoutConstraint:[e-mail]#38 UIView:0x7fcd8580dad0.width == UIView:0x7fcd8580dad0.height>

当我删除居中约束make.center.equalToSuperview() 时，这不会出现。但是，它放错了位置。

故事板和我的代码有什么不同？我真的不明白这一点。我也尝试使用默认的 swift 语法，结果完全一样。所以我认为SnapKit没有问题

有什么想法吗？谢谢你们的帮助。如果您需要更多信息，请告诉我。

编辑：我混淆了一些东西。这与图像及其纵横比无关。这只是一个UIView，它应该在适合矩形的同时保持特定的纵横比。实际图像将被放入holderView。对不起

【问题讨论】：

为什么 imageView 不简单地链接到支架边缘并使用 .scaleAspectFit 的任何原因？

很难解释，但我会尝试：我有一个collection view，里面充满了不同大小的单元格。每个单元格都被设置为.scaleAspectFill 的UIImageView（链接到单元格的边缘）覆盖。现在我需要在另一个view controller 中以较小的形式表示带有图像的单元格，您可以在其中移动它以放置/旋转/缩放图像（aspectFill '缩放'图像以适应，你应该能够有点说它是如何放置在单元格中的）

我意识到这与ImageView 无关，真的。我要编辑标题。该图像确实只是链接到holderViews 边缘。它的持有者视图必须具有单元格的纵横比。抱歉，我弄混了

你有太多的限制。您可以约束两条边和宽度/高度或中心和宽度/高度或四个边（如果您使用纵横比约束，则仅设置宽度或高度）

看起来您正在尝试将 imageView 的 width 设置为等于 imageView * 3/2 的 height... 但您也是 将 imageView 的边缘设置为其父视图。您可能想要设置一个或另一个，而不是两者。

【参考方案1】：

好的 - 这是一种方法。

获取子视图的“原生”大小，计算“纵横比”比率 - 即适合父视图的宽度或高度的比率，并适当缩放其他维度。

然后，使用centerXAnchor 和centerYAnchor 定位子视图，并使用widthAnchor 和heightAnchor 调整大小。

注意：如果您要放置图像，请根据图像大小计算宽高比大小，将图像放入图像视图中，将图像视图缩放模式设置为fill ，最后将约束应用于图像视图。

您应该能够按原样运行此示例。只需使用顶部的“本机”大小值，看看它如何将子视图融入到父视图中。

public class AspectFitViewController : UIViewController 

    // "native" size for the holderView
    let hViewWidth: CGFloat = 700.0
    let hViewHeight: CGFloat = 200.0

    let topView: UIView = 
        let v = UIView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = UIColor.blue
        return v
    ()

    let holderView: UIView = 
        let v = UIView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = UIColor.cyan
        return v
    ()

    public override func viewDidLoad() 
        super.viewDidLoad()
        view.bounds = CGRect(x: 0, y: 0, width: 400, height: 600)
        view.backgroundColor = .yellow

        // add topView
        view.addSubview(topView)

        // pin topView to leading / top / trailing
        topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
        topView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
        topView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true

        // explicit height for topView
        topView.heightAnchor.constraint(equalToConstant: 250.0).isActive = true

        // add holderView to topView
        topView.addSubview(holderView)

        // center X and Y
        holderView.centerXAnchor.constraint(equalTo: topView.centerXAnchor, constant: 0.0).isActive = true
        holderView.centerYAnchor.constraint(equalTo: topView.centerYAnchor, constant: 0.0).isActive = true

        // holderView's width and height will be calculated in viewDidAppear
        // after topView has been laid-out by the auto-layout engine

    

    public override func viewDidAppear(_ animated: Bool) 
        super.viewDidAppear(animated)

        let aspectWidth  = topView.bounds.size.width / hViewWidth
        let aspectHeight = topView.bounds.size.height / hViewHeight

        let aspectFit = min(aspectWidth, aspectHeight)

        let newWidth = hViewWidth * aspectFit
        let newHeight = hViewHeight * aspectFit

        holderView.widthAnchor.constraint(equalToConstant: newWidth).isActive = true
        holderView.heightAnchor.constraint(equalToConstant: newHeight).isActive = true

    

---

编辑：

澄清后...这可以仅通过约束来完成。关键是“优先级1000”top和leading约束必须.greaterThanOrEqual为零，bottom和trailing约束必须.lessThanOrEqual为零。

public class AspectFitViewController : UIViewController 

    // "native" size for the holderView
    let hViewWidth: CGFloat = 700.0
    let hViewHeight: CGFloat = 200.0

    let topView: UIView = 
        let v = UIView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = UIColor.blue
        return v
    ()

    let holderView: UIView = 
        let v = UIView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = UIColor.cyan
        return v
    ()

    public override func viewDidLoad() 
        super.viewDidLoad()
        view.bounds = CGRect(x: 0, y: 0, width: 400, height: 600)
        view.backgroundColor = .yellow

        // add topView
        view.addSubview(topView)

        // pin topView to leading / top / trailing
        topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
        topView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
        topView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true

        // explicit height for topView
        topView.heightAnchor.constraint(equalToConstant: 250.0).isActive = true

        // add holderView to topView
        topView.addSubview(holderView)

        // center X and Y
        holderView.centerXAnchor.constraint(equalTo: topView.centerXAnchor, constant: 0.0).isActive = true
        holderView.centerYAnchor.constraint(equalTo: topView.centerYAnchor, constant: 0.0).isActive = true

        // aspect ratio size
        holderView.widthAnchor.constraint(equalTo: holderView.heightAnchor, multiplier: hViewWidth / hViewHeight).isActive = true

        // two constraints for each side...
        // the .equal constraints need .defaultLow priority
        // top and leading constraints must be .greaterThanOrEqual to 0
        // bottom and trailing constraints must be .lessThanOrEqual to 0

        let topA = NSLayoutConstraint(item: holderView, attribute: .top, relatedBy: .greaterThanOrEqual, toItem: topView, attribute: .top, multiplier: 1.0, constant: 0.0)
        let topB = NSLayoutConstraint(item: holderView, attribute: .top, relatedBy: .equal, toItem: topView, attribute: .top, multiplier: 1.0, constant: 0.0)

        let bottomA = NSLayoutConstraint(item: holderView, attribute: .bottom, relatedBy: .lessThanOrEqual, toItem: topView, attribute: .bottom, multiplier: 1.0, constant: 0.0)
        let bottomB = NSLayoutConstraint(item: holderView, attribute: .bottom, relatedBy: .equal, toItem: topView, attribute: .bottom, multiplier: 1.0, constant: 0.0)

        let leadingA = NSLayoutConstraint(item: holderView, attribute: .leading, relatedBy: .greaterThanOrEqual, toItem: topView, attribute: .leading, multiplier: 1.0, constant: 0.0)
        let leadingB = NSLayoutConstraint(item: holderView, attribute: .leading, relatedBy: .equal, toItem: topView, attribute: .leading, multiplier: 1.0, constant: 0.0)

        let trailingA = NSLayoutConstraint(item: holderView, attribute: .trailing, relatedBy: .lessThanOrEqual, toItem: topView, attribute: .trailing, multiplier: 1.0, constant: 0.0)
        let trailingB = NSLayoutConstraint(item: holderView, attribute: .trailing, relatedBy: .equal, toItem: topView, attribute: .trailing, multiplier: 1.0, constant: 0.0)

        topB.priority = .defaultLow
        bottomB.priority = .defaultLow
        leadingB.priority = .defaultLow
        trailingB.priority = .defaultLow

        NSLayoutConstraint.activate([
            topA, topB,
            bottomA, bottomB,
            leadingA, leadingB,
            trailingA, trailingB
            ])

    

【讨论】：

感谢您的回答。我以前有一个类似的版本（虽然它不太好用。你的版本运行良好），但是当它应该在不手动计算任何东西的情况下工作时，我发现这有点不方便。 （它使用故事板工作，所以它必须工作也只能使用代码。这就是我不明白的）。但是我想如果没有人知道代码为什么不起作用，我将不得不手动坚持计算宽度/高度。无论如何，谢谢。

@Quantm - 啊 --- 现在我明白了。请参阅我编辑的答案，特别是 cmets。

哇，这确实有效（虽然我认为应该是hViewHeight / hViewWidth，而不是hViewWidth / hViewHeight）。但为什么它应该是 lessThanOrEqualTo 呢？我不太明白。这不应该意味着零件可以在屏幕外吗？但非常感谢您的努力。我真的很感激！

哎呀 - 我调换了宽高比...现在已修复。当您在故事板中设置尾随和底部约束时，IB 会自动设置 First Item: Superview, Second Item: Subview... 所以它是>= 0。从代码中设置它通常更容易根据“子视图到超级视图”来思考，因此您需要将其设为<= 0。编码为“我希望它距底部 20 分”并且在将其设置为 +20 而不是 -20 时出错非常常见。

ooooohhhh，该死的。对，我从来没想过。说得通。谢谢！ :)