如何使用AutoLayout从UIView子类获取框架

Question

我有一个自定义的UIView子类，在其中以编程方式添加了几个子视图。 我正在使用AutoLayout设置所有布局代码。

当我重写UIView的layoutSubviews()方法以尝试获取子视图框架时，就会出现问题，因为它们总是返回.zero作为框架。

但是，如果我转到XCode中的View Hiearchy Debugger，则会计算并正确显示所有帧。

这是我在layoutSubviews()方法中记录的控制台输出：

layoutSubviews(): <PrologueTextView: 0x7fa50961abc0; frame = (19.75 -19.5; 335.5 168); clipsToBounds = YES; autoresize = RM+BM; layer = <CAShapeLayer: 0x60000022be20>>
layoutSubviews(): <Label: 0x7fa509424c60; baseClass = UILabel; frame = (0 0; 0 0); text = 'This is'; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x60400028d160>>
layoutSubviews(): <Label: 0x7fa509424f60; baseClass = UILabel; frame = (0 0; 0 0); text = 'some sample'; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x60400028d2a0>>
layoutSubviews(): <Label: 0x7fa509425260; baseClass = UILabel; frame = (0 0; 0 0); text = 'text for you'; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x60400028d3e0>>

这是我的UIView子类相关代码：

internal class PrologueTextView: UIView {
    internal var labels: [UILabel] = []
    internal let container: UIVisualEffectView = UIVisualEffectView()

    // region #Properties
    internal var shapeLayer: CAShapeLayer? {
        return self.layer as? CAShapeLayer
    }

    internal override class var layerClass: AnyClass {
        return CAShapeLayer.self
    }
    // endregion

    // region #Initializers
    internal override init(frame: CGRect) {
        super.init(frame: frame)
        self.setup()
    }

    internal required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.setup()
    }
    // endregion

    // region #UIView lifecycle
    internal override func layoutSubviews() {
        super.layoutSubviews()

        let mask: UIBezierPath = UIBezierPath()

        for label in self.labels {
            let roundedCorners = self.roundedCorners(for: label)
            let maskBezierPath = UIBezierPath(roundedRect: label.frame, byRoundingCorners: roundedCorners, cornerRadius: 4.0)
            mask.append(maskBezierPath)
        }

        self.shapeLayer?.path = mask.cgPath

        print("layoutSubviews(): \(self)")
        print("layoutSubviews(): \(labels[0])")
        print("layoutSubviews(): \(labels[1])")
        print("layoutSubviews(): \(labels[2])")
    }
    // endregion

    // region #Helper methods
    private func setup() {
        self.setupSubviews()
        self.setupSubviewsAnchors()
    }

    private func setupSubviews() {
        self.container.effect = UIBlurEffect(style: .light)
        self.container.translatesAutoresizingMaskIntoConstraints = false

        self.addSubview(self.container)

        let someSampleText = "This is\nsome sample\ntext for you"

        for paragraph in someSampleText.components(separatedBy: "\n") {
            let label = UILabel()
                label.text = paragraph
                label.translatesAutoresizingMaskIntoConstraints = false

            self.labels.append(label)

            self.container.contentView.addSubview(label)
        }
    }

    private func setupSubviewsAnchors() {
        NSLayoutConstraint.activate([
            self.container.topAnchor.constraint(equalTo: self.topAnchor),
            self.container.bottomAnchor.constraint(equalTo: self.bottomAnchor),
            self.container.leadingAnchor.constraint(equalTo: self.leadingAnchor),
            self.container.trailingAnchor.constraint(equalTo: self.trailingAnchor)
        ])

        for (index, label) in self.labels.enumerated() {
            let offset = 16.0 * CGFloat(index)

            if index == 0 {
                label.topAnchor.constraint(equalTo: self.container.contentView.topAnchor).isActive = true
            } else {
                let prev = self.labels[index - 1]
                label.topAnchor.constraint(equalTo: prev.bottomAnchor).isActive = true

                if index == self.labels.count - 1 {
                    label.bottomAnchor.constraint(equalTo: self.container.contentView.bottomAnchor).isActive = true
                }
            }

            NSLayoutConstraint.activate([
                label.leadingAnchor.constraint(equalTo: self.container.leadingAnchor, constant: offset),
                label.trailingAnchor.constraint(lessThanOrEqualTo: self.container.trailingAnchor)])
        }
    }

    private func roundedCorners(for label: Label) -> UIRectCorner {
        switch label {
        case self.labels.first:
            return [.topLeft, .topRight, .bottomRight]
        case self.labels.last:
            return [.topRight, .bottomLeft, .bottomRight]
        default:
            return [.topRight, .bottomLeft]
        }
    }
    // endregion
}

那么，在AutoLayout计算并设置视图及其子视图的框架之后，是否有任何UIView方法会被调用？

Answer 1

您需要在打印行之前调用self.container.layoutIfNeeded()

internal class PrologueTextView: UIView {
    internal var labels: [UILabel] = []
    internal let container: UIVisualEffectView = UIVisualEffectView()

    // region #Properties
    internal var shapeLayer: CAShapeLayer? {
        return self.layer as? CAShapeLayer
    }

    internal override class var layerClass: AnyClass {
        return CAShapeLayer.self
    }
    // endregion

    // region #Initializers
    internal override init(frame: CGRect) {
        super.init(frame: frame)
        self.setup()
    }

    internal required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.setup()
    }
    // endregion

    // region #UIView lifecycle
    internal override func layoutSubviews() {
        super.layoutSubviews()

        let mask: UIBezierPath = UIBezierPath()

        for label in self.labels {
            let roundedCorners = self.roundedCorners(for: label)
            let maskBezierPath = UIBezierPath(roundedRect: label.frame, byRoundingCorners: roundedCorners, cornerRadii: CGSize(width: 20, height: 20))
            mask.append(maskBezierPath)
        }

        self.shapeLayer?.path = mask.cgPath

        self.container.layoutIfNeeded()  // here

        print("layoutSubviews(): \(self)")
        print("layoutSubviews(): \(labels[0])")
        print("layoutSubviews(): \(labels[1])")
        print("layoutSubviews(): \(labels[2])")
    }
    // endregion

    // region #Helper methods
    private func setup() {
        self.setupSubviews()
        self.setupSubviewsAnchors()
    }

    private func setupSubviews() {
        self.container.effect = UIBlurEffect(style: .light)
        self.container.translatesAutoresizingMaskIntoConstraints = false

        self.addSubview(self.container)

        let someSampleText = "This is\nsome sample\ntext for you"

        for paragraph in someSampleText.components(separatedBy: "\n") {
            let label = UILabel()
            label.text = paragraph
            label.translatesAutoresizingMaskIntoConstraints = false

            self.labels.append(label)

            self.container.contentView.addSubview(label)
        }
    }

    private func setupSubviewsAnchors() {
        NSLayoutConstraint.activate([
            self.container.topAnchor.constraint(equalTo: self.topAnchor),
            self.container.bottomAnchor.constraint(equalTo: self.bottomAnchor),
            self.container.leadingAnchor.constraint(equalTo: self.leadingAnchor),
            self.container.trailingAnchor.constraint(equalTo: self.trailingAnchor)
            ])

        for (index, label) in self.labels.enumerated() {
            let offset = 16.0 * CGFloat(index)

            if index == 0 {
                label.topAnchor.constraint(equalTo: self.container.contentView.topAnchor).isActive = true
            } else {
                let prev = self.labels[index - 1]
                label.topAnchor.constraint(equalTo: prev.bottomAnchor).isActive = true

                if index == self.labels.count - 1 {
                    label.bottomAnchor.constraint(equalTo: self.container.contentView.bottomAnchor).isActive = true
                }
            }

            NSLayoutConstraint.activate([
                label.leadingAnchor.constraint(equalTo: self.container.leadingAnchor, constant: offset),
                label.trailingAnchor.constraint(lessThanOrEqualTo: self.container.trailingAnchor)])
        }
    }

    private func roundedCorners(for label: UILabel) -> UIRectCorner {
        switch label {
        case self.labels.first:
            return [.topLeft, .topRight, .bottomRight]
        case self.labels.last:
            return [.topRight, .bottomLeft, .bottomRight]
        default:
            return [.topRight, .bottomLeft]
        }
    }
    // endregion
}

Answer 2

@available（iOS 6.0，*）open func updateConstraints（）//重写它，以在约束更新过程中调整您的特殊约束

在super.updateConstraints（）框架之后应具有正确的大小

Answer 3

在与之抗争之后，我弄清楚了发生了什么。

layoutSubviews()确实是必经之路。 它将计算视图及其直接子视图的框架。

这里的问题是UILabels不是主UIView子类的子视图，而是主UIView子视图（效果视图）的子视图。

您的视图层次结构示例：

--> TestView
    --> EffectView
        --> UILabel
        --> UILabel
        --> UILabel

如您所见，由于layoutSubviews()是直接子视图，因此layoutSubviews()将为您提供正确的TestView和EffectView框架，但由于它们不是TestView的直接子视图，因此不会为您提供UILabels的计算框架。