如何以编程方式设置 UIScrollView 以使用 autoLayout 水平滚动

Question

我正在尝试实现一种行为，即我在表格视图中有一个最小宽度的表单。所以基本上，如果屏幕很宽，视图只会垂直滚动，但当屏幕很窄时，表单会缩小到最小宽度，然后开始水平滚动，以免内容松动。所以，我需要使用 autoLayout 来设置这些约束，并且我想以编程方式进行（因为我正在使用框架）。

问题是，我根本无法让视图水平滚动。我已经阅读了我能找到的所有内容，并尝试了我能想到的所有内容，但没有任何效果。现在我尝试在我的视图中添加一张大图片并让它滚动两个方向，但我无法让它工作。

这是我的层次结构：

>UIView
>>UIScrollView
>>>ContentView (UIView)
>>>>ImageView

这是我的代码：

   override func viewDidLoad() {
    if scrollView == nil {
        scrollView = UIScrollView(frame: view.bounds)
        scrollView.backgroundColor = .groupTableViewBackground
        scrollView.isDirectionalLockEnabled = true
        scrollView.showsHorizontalScrollIndicator = true
    }
    if scrollView.superview == nil {
        view.addSubview(scrollView)

        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true

        let contentView = UIView(frame: view.bounds)
        scrollView.addSubview(contentView)

        contentView.translatesAutoresizingMaskIntoConstraints = false
        contentView.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true
        contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
        contentView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true

        let a = contentView.heightAnchor.constraint(equalTo: scrollView.heightAnchor)
        let b = contentView.widthAnchor.constraint(equalTo: scrollView.widthAnchor)
        a.priority = .defaultLow
        b.priority = .defaultLow
        a.isActive = true
        b.isActive = true

        let image = MyImage.icon(named: "myImage", of: CGSize(width: 1000, height: 1000))
        let imageView = UIImageView(image: image)

        imageView.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(imageView)

        imageView.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        imageView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true

    }
    super.viewDidLoad()
}

当我调试视图层次结构时，我可以看到图像的大小仍然是正确的(1000, 1000)，但是滚动视图的内容大小没有更新并且图片被截断，没有滚动。

<UIScrollView: 0x11ead5c00; frame = (0 0; 834 1112); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x1c8853800>; layer = <CALayer: 0x1c8c32240>; contentOffset: {0, -64}; contentSize: {834, 1112}; adjustedContentInset: {64, 0, 0, 0}>

<UIImageView: 0x11a89b000; frame = (0 0; 1000 1000); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1c8231c80>>

我发现并查看了这个示例以编程方式设置滚动视图https://github.com/zaxonus/AutoLayScroll。它垂直滚动，但为此，我无法将其设置为水平滚动。

请帮忙，我忽略了什么？

Answer 1

要使您的示例 scrollView 内容大小为 1000x1000，只需将这些约束添加到 imageView：

imageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
imageView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true

没有它们，您的contentView 不知道它应该包装imageView，因此它的大小是根据低优先级约束a 和b 计算的

Answer 2

感谢 Anton，我成功了！如果其他人正在尝试做我想做的事，我只是想分享我的最终解决方案。

通过以下代码，您可以向 Eureka 框架 FormViewController (https://github.com/xmartlabs/Eureka) 的表单添加水平滚动功能。

import UIKit
import Eureka

class MyScrollableViewController: FormViewController {

    var scrollView: UIScrollView!
    var minimumWidth: CGFloat = 500.0

    override func viewDidLoad() {
        if tableView == nil {
            tableView = UITableView(frame: view.bounds, style: .grouped)
            if #available(iOS 9.0, *) {
                tableView.cellLayoutMarginsFollowReadableWidth = false
            }
        }
        if scrollView == nil {
            scrollView = UIScrollView(frame: view.bounds)
            scrollView.backgroundColor = .groupTableViewBackground
            scrollView.isDirectionalLockEnabled = true
            scrollView.showsHorizontalScrollIndicator = true
        }
        if scrollView.superview == nil && tableView.superview == nil {
            view.addSubview(scrollView)

            scrollView.translatesAutoresizingMaskIntoConstraints = false
            scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
            scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
            scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true

            let contentView = UIView(frame: view.bounds)
            scrollView.addSubview(contentView)

            contentView.translatesAutoresizingMaskIntoConstraints = false
            contentView.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
            contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true
            contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
            contentView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true

            let a = contentView.heightAnchor.constraint(equalTo: scrollView.heightAnchor)
            let b = contentView.widthAnchor.constraint(equalTo: scrollView.widthAnchor)
            a.priority = .defaultLow
            b.priority = .defaultLow
            a.isActive = true
            b.isActive = true

            contentView.addSubview(tableView)
            tableView.translatesAutoresizingMaskIntoConstraints = false
            tableView.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
            tableView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
            tableView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
            tableView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
            tableView.widthAnchor.constraint(greaterThanOrEqualToConstant: minimumWidth).isActive = true
        }
        // Has to be called after setting up the tableView since we override the Eureka default setup
        super.viewDidLoad()

        // Setup your Eureka form as usual
        form +++ Section()
            <<< LabelRow { row in
                row.title = "My first row"
        }
    }
}