iOS自定义View 控件自动计算size能力

背景

在使用 UILabel 和 UIImage 的时候，不用指定宽高约束，控件也不会报约束缺失，还可以根据内容自己确定适合的宽高，特别适合 Xib 和 Storyboard 布局。

我们在自定义控件的时候，怎么才能让控件具备这种自动计算宽高的功能了？

基本知识点

只需要自定义控件满足以下条件之一即可：

自定义控件实现intrinsicContentSize的重写并返回合适大小，适合子控件存在 frame初始化，或者动态添加。
自定义控件内部约束满足

这时候有部分长得帅的小伙伴要问了，如果自定义控件即满足了所有约束，又重写了intrinsicContentSize返回了计算大小怎么办。答案只有一个，执行约束，忽略这时候有部分长得帅的小伙伴要问了，如果自定义控件即满足了所有约束，又重写了intrinsicContentSize返回了计算大小怎么办。答案只有一个，执行约束，忽略 intrinsicContentSize.

intrinsicContentSize

intrinsicContentSize又叫内容大小，决定了控件自动布局下的大小，（当控件没有宽高约束的时候，系统会自动添加宽高约束）自定义控件重写 intrisicContentsize 返回内在大小，自动布局系统就可以自己确定控件大小，就像使用UILabel,根据文本多少弹性控制大小。

自定义控件如果要适配AutoLayout, 达到自动适应的效果，则需要重写此属性。

 override var intrinsicContentSize: CGSize {// 计算内容大小， 如果某个维度不使用内在大小可以设置为 UIView.noIntrinsicMetric//return CGSize(width: bounds.width, height: itemHeight*CGFloat(items.count))//返回计算的size}

UIView.noIntrinsicMetric

内在大小需要返回 CGSize, 就是你希望控件的内在大小。

但是可能存在，我的控件只想指定高度，宽度随外部约束。这时候就需要使用UIView.noIntrinsicMetric使用-1也可以，同样的效果。

比如 UIView 的内在大小默认值等于（UIView.noIntrinsicMetric,UIView.noIntrinsicMetric）也就是（-1，-1），表示宽高由外部控件外部约束决定，或者有创建的自动约束决定。

一旦重写并返回非noIntrinsicMetric, 那么控件自己就会为自己添加对应的约束。

比如我重写

 override var intrinsicContentSize: CGSize {return CGSize(width: UIView.noIntrinsicMetric, height: itemH)}

打印约束自动添加

<NSContentSizeLayoutConstraint:0x600003650960 AnyTest.SequenceView:0x7fc91bf0a1b0.height == 162.5 Hug:250 CompressionResistance:750   (active)>

invalidateIntrinsicContentSize()

该方法的作用是重新计算intrinsicContentSize,相当于原来的内置大小失效，重新生效一个新的。

func invalidateIntrinsicContentSize()

通常需要内在大小改变时候调用，如外部数据变化时。

约束调整周期

一般情况调用顺序

invlidateIntricContentSize() --> intrisicContenSize --> updateConstraints 之后会调用 layoutSubviews()。

如 UILabel 调整周期如下：

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调整contentSize

layoutSubviews 方法

updateConstraints 方法

初始化

intrinsicContentSize

invalidateIntrinsicContentSize 方法

约束结束

虚线表示可能调用，可能某些步骤存在重复调用。

我们需要在合适的时机去调用invalidateIntrinsicContentSize()方法以返回正确的内在大小。

比如当某个属性改变可能引起控件的内在大小改变时调用该方法，比如UILabel设置文本的时候应该会调用这个方法（猜测）。

但要注意跳出循环(可能会引起循环)。

override func layoutSubviews() {super.layoutSubviews()//if intrinsicContentSize() != bound.size {//计算相应的内置大小invalidateIntrinsicContentSize() // 重置内容大小。//}
}

sizeToFit()

调整子视图大小和位置（不能重写）,可以在外部或者内部调用，如果使内部调用，可以使得控件本身基于外部约束获取大小值（

func sizeToFit()

计算和返回视图合适的尺寸

/// size参数： 给定大小
func sizeThatFits(_ size: CGSize) -> CGSize

自定义View内部宽度，可以在layousubViews中调用super.layoutSubviews后获得准确宽度。

 override func layoutSubviews() {super.layoutSubviews()print(frame)  // 这里获取的宽度是准备的。
}

sizeTofit简单使用与理解（laughing–简书）

实例代码

   @objc private func tap(){//此处引起内在大小改变为点击事件。self.invalidateIntrinsicContentSize()  //先使内置大小无效，自动调用重写内置大小。// 改变的数据extentSize = CGSize(width: 0, height: 20)}// 重写改变内置大小override var intrinsicContentSize: CGSize{// 返回新大小return CGSize(width: bounds.width, height: bounds.height+extentSize.height)}

使用实例：只有20%的iOS程序员能看懂(自定义控件的随内容变换而自适应大小)

返回最佳的大小，基于当前的约束

// targetSize: layoutFittingCompressedSize(尽可能小) layoutFittingExpandedSize（尽可能大）
func systemLayoutSizeFitting(_ targetSize: CGSize) -> CGSize

/// targetSize: 目标大小 如果需要尽可能小 使用layoutFittingCompressedSize， layoutFittingCompressedSize(尽可能大)
/// horizontalFittingPriority: 水平约束的优先级。指定fittingSizeLevel以获得尽可能接近targetSize宽度值的宽度
/// verticalFittingPriority: 垂直约束的优先级。指定fittingSizeLevel以获得尽可能接近targetSize高度值的高度
func systemLayoutSizeFitting(_ targetSize: CGSize, withHorizontalFittingPriority horizontalFittingPriority: UILayoutPriority, verticalFittingPriority: UILayoutPriority) -> CGSize

参考：

github某issues 关于AutoLayout的讨论推荐

Apple Autolayout相关文档

疑问

UILabel 的内部怎么计算出内在大小的？

即在intrinsicContentSize属性返回值是怎么计算的。按照打印日志来看，是经过多次（超过四次）updateLayout, intrinsicContenSize调用得出的。

自定义视图实现了 intrinsicContentSize，如何适配在UITableViewCell中自适应行高？

经过测试，自定义视图实现intrinsicContentSize，会使用第一次返回的内置大小，如果是通过多次invalidateIntrinsicContentSize来确定内置大小，在UITableViewCell中使用将不会达到想要的效果。

参考

Intrinsic Content Size of Multi-Line Text

iOS 中编码约束

实例

实现如下自定义控件，外部传入黄色 view 数量，等比例计算黄色高度，计算intrinsicContentSize

示例代码

override var intrinsicContentSize: CGSize {return CGSize(width: UIView.noIntrinsicMetric, height: itemH)
}

layoutSubviews

     override func layoutSubviews() {super.layoutSubviews()updateItemsLayout()invalidateIntrinsicContentSize()}

完整代码

import UIKit
@IBDesignable
class SequenceView: UIView {@IBInspectablevar count: Int = 0 {didSet {updateItemsCount()}}private var items: [UIView] = []private var itemH: CGFloat = 0override var intrinsicContentSize: CGSize {return CGSize(width: UIView.noIntrinsicMetric, height: itemH)}override init(frame: CGRect) {super.init(frame: frame)commonInit()}required init?(coder: NSCoder) {super.init(coder: coder)commonInit()heightAnchor.constraint(equalToConstant: 200).isActive = true}override func layoutSubviews() {super.layoutSubviews()updateItemsLayout()invalidateIntrinsicContentSize()}override func prepareForInterfaceBuilder() {count = 3}
}private extension SequenceView {func commonInit() {count = 0backgroundColor = .gray}func updateItemsCount() {items.forEach { $0.removeFromSuperview() }items = []items = (0 ..< count).map { _ in createItem() }}func updateItemsLayout() {guard count > 0 else {return}let space: CGFloat = 10let itemW = (bounds.size.width - (CGFloat(count - 1)*space)) / CGFloat(count)itemH = itemWfor (index, item) in items.enumerated() {// 根据 控件当前自身宽度 计算 item 高度，设置 frame 。item.frame = CGRect(x: CGFloat(index)*(space + itemW), y: 0, width: itemW, height: itemH)}}func createItem() -> UIView {let view = UIView()view.backgroundColor = .yellowaddSubview(view)return view}
}