用于 ScrollView 和粘性页脚的 iOS Autolayout

Question

假设我的布局如下图所示: Root View - 是 viewController 的 View 。我希望我的页脚文本是

• 如果内容适合一个屏幕(主要文本很小)，则粘在屏幕底部
• 在其他情况下距正文 15pt，距屏幕底部 15pt

我知道，我可以计算主要文本高度并将其与当前屏幕尺寸进行比较，但我想找到另一种方法(理想情况下只有在有限制的情况下)。

这可能吗？

Answer 1

要实现您正在尝试做的事情，您需要设置以下约束:

ScrollView :
- top、leading、trailing 和 bottom 等于 RootView 的 top、leading、trailing 和 bottom

包装 View :
- top、leading、trailing 和 bottom 等于 ScrollView 的 top、leading、trailing 和 bottom
- width 等于 ScrollView 的 width
- height greaterThanOrEqual to ScrollView 的 height

TextView :
- top, leading 和 trailing 等于 WrapperView 的 top, leading 和 trailing

页脚 View :
- leading 和trailing 等于WrapperView 的leading 和trailing
- bottom 等于 WrapperView 的 bottom(常量为 15)
- top greaterThanOrEqual to TextView's bottom (常量为 15)

关键是使用 greaterThanOrEqual 关系的两个约束:WrapperView 至少与 ScrollView 和 一样高>FooterView 的顶部距离 TextView 的底部至少有 15 的距离。

以下是使用 Storyboard时的限制条件:

这就是您以编程方式(使用 SnapKit)执行此操作的方式:

import UIKit
import SnapKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let scrollView = UIScrollView()
        view.addSubview(scrollView)

        let wrapperView = UIView()
        wrapperView.backgroundColor = .cyan
        scrollView.addSubview(wrapperView)

        let textView = UILabel()
        textView.numberOfLines = 0
        textView.font = UIFont.systemFont(ofSize: 30)
        textView.text = "You think water moves fast? You should see ice. It moves like it has a mind. Like it knows it killed the world once and got a taste for murder. After the avalanche, it took us a week to climb out. Now, I don't know exactly when we turned on each other, but I know that seven of us survived the slide... and only five made it out. Now we took an oath, that I'm breaking now. We said we'd say it was the snow that killed the other two, but it wasn't. Nature is lethal but it doesn't hold a candle to man."
        //textView.text = "You think water moves fast? You should see ice. It moves like it has a mind."
        textView.backgroundColor = .yellow
        wrapperView.addSubview(textView)

        let footer = UILabel()
        footer.textAlignment = .center
        footer.text = "Footer text"
        footer.backgroundColor = .orange
        wrapperView.addSubview(footer)

        scrollView.snp.makeConstraints { (make) in
             make.edges.equalTo(view)
        }

        wrapperView.snp.makeConstraints { (make) in
            make.edges.equalTo(scrollView)
            make.width.equalTo(scrollView)
            make.height.greaterThanOrEqualTo(scrollView)
        }
        textView.snp.makeConstraints { (make) in
            make.top.left.right.equalTo(0)
        }
        footer.snp.makeConstraints { (make) in
            make.top.greaterThanOrEqualTo(textView.snp.bottom).offset(15)
            make.left.right.equalTo(0)
            make.bottom.equalTo(-15)
        }
    }
}

长文本截图:

带有短文本的屏幕截图: