ios - 如何在 UIScrollView 上修复 UIButton？

Question

我的 UIScrollView 上有一个 UIButton，当我缩放 ScrollView 时，按钮位置不固定……有没有办法让它固定在一个位置？

Answer 1

从 iOS 11 开始，UIScrollView有一个名为 frameLayoutGuide 的实例属性. frameLayoutGuide有以下声明:

var frameLayoutGuide: UILayoutGuide { get }

The layout guide based on the untransformed frame rectangle of the scroll view.

Use this layout guide when you want to create Auto Layout constraints that explicitly involve the frame rectangle of the scroll view itself, as opposed to its content rectangle.

以下 Swift 5.1/iOS 13 UIViewController实现展示了如何使用 frameLayoutGuide为了使 UIButton 居中在 UIScrollView 内.

import UIKit

class ViewController: UIViewController {

    let scrollView = UIScrollView()
    let button = UIButton(type: .system)
    let imageView = UIImageView(image: UIImage(named: "LargeImage"))

    override func viewDidLoad() {
        super.viewDidLoad()

        // Set scrollView constraints
        scrollView.contentInsetAdjustmentBehavior = .never
        view.addSubview(scrollView)
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            scrollView.topAnchor.constraint(equalTo: view.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])

        // Set imageView constraints
        scrollView.addSubview(imageView)
        imageView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            imageView.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor),
            imageView.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.trailingAnchor),
            imageView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor),
            imageView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor)
        ])

        // Set button constraints (centered)
        button.setTitle("Button", for: .normal)
        scrollView.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: scrollView.frameLayoutGuide.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: scrollView.frameLayoutGuide.centerYAnchor)
        ])
    }

}