UIScrollView 项目不从后台移动

Question

我设置了我的约束，以便在您加载时我会有一个图表占据屏幕，但您可以向下滚动以查看更多信息。但是，我看到滚动条在动，而图表没有动！

var scrollView: UIScrollView {
    let scroll = UIScrollView()
    self.view.addSubview(scroll)
    scroll.snp.makeConstraints { (make) in
        make.edges.equalTo(self.view)
    }
    return scroll

}
var contentView: UIView {
    let content = UIView()
    self.scrollView.addSubview(content)
    content.snp.makeConstraints { (make) in
        make.top.bottom.equalTo(self.scrollView)
        make.left.right.equalTo(self.view)
        make.width.equalTo(self.scrollView)
    }
    // self.scrollView.contentSize = content.frame.size
    return content
}
override func viewDidLoad() {
    super.viewDidLoad()
    self.contentView.addSubview(self.chart)

    self.chart.snp.makeConstraints { (make) in
        // http://snapkit.io/docs/
        // https://github.com/SnapKit/SnapKit/issues/448
        make.top.equalTo(self.contentView)
        make.left.right.equalTo(self.contentView)
        make.height.equalTo(self.view).offset(-(self.tabBarController?.tabBar.frame.height)!)
    }
    self.scrollView.contentSize = CGSize(width: self.view.frame.width, height: 3000) // Testing

}

所以滚动条动了，但是内容没动。

Answer 1

不幸的是，你做错了很多事情。

首先，当你使用这个结构时：

var scrollView: UIScrollView {
    let scroll = UIScrollView()
    self.view.addSubview(scroll)
    scroll.snp.makeConstraints { (make) in
        make.edges.equalTo(self.view)
    }
    return scroll
}

每次你引用scrollView你正在创建另一个 滚动视图的实例。运行你的代码，并使用 Debug View Hierarchy，这就是你得到的：

red 视图是滚动视图，blue 视图是内容视图。如您所见，这绝对不是您想要的。

下面是一个示例，说明您可以如何做您想做的事情：

class ViewController: UIViewController {

    var scrollView: UIScrollView = {
        let scroll = UIScrollView()
        scroll.backgroundColor = .red
        return scroll

    }()

    var contentView: UIView  = {
        let content = UIView()
        content.backgroundColor = .blue
        return content
    }()

    var chart: UILabel = {
        let v = UILabel()
        v.numberOfLines = 0
        v.text = "This is the\nChart View"
        v.backgroundColor = .cyan
        v.textAlignment = .center
        return v
    }()

    var bottomLabel: UILabel = {
        let v = UILabel()
        v.text = "The Bottom Label"
        v.backgroundColor = .yellow
        v.textAlignment = .center
        return v
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        // add scrollView
        self.view.addSubview(scrollView)

        // constrain to safe area (so it doesn't extend below the tab bar)
        scrollView.snp.makeConstraints { (make) in
            make.edges.equalTo(self.view.safeAreaLayoutGuide)
        }

        // add contentView to scrollView
        self.scrollView.addSubview(contentView)

        // constrain all 4 edges to scrollView
        // this will allow auto-layout to control / define the .contentSize
        contentView.snp.makeConstraints { (make) in
            make.edges.equalTo(self.scrollView)
        }

        // constrain contentView's width to scrollView's width
        // but we *don't* constrain its height
        contentView.snp.makeConstraints { (make) in
            make.width.equalTo(self.scrollView)
        }

        // add the chart to contentView
        self.contentView.addSubview(self.chart)

        // constrain chart to top, left and right of contentView
        // constrain its height to scrollView's height (so it initially fills the visible area
        chart.snp.makeConstraints { (make) in
            make.top.equalTo(self.contentView)
            make.left.right.equalTo(self.contentView)
            make.height.equalTo(self.scrollView)
        }

        // now, we'll add a label to scrollView
        self.contentView.addSubview(self.bottomLabel)

        // constrain the label left and right with 20-pts, and a height of 40
        bottomLabel.snp.makeConstraints { (make) in
            make.left.equalTo(self.contentView).offset(20)
            make.right.equalTo(self.contentView).offset(-20)
            make.height.equalTo(40)
        }

        // constrain the label's TOP 20-pts below the BOTTOM of chart view
        bottomLabel.snp.makeConstraints { (make) in
            make.top.equalTo(self.chart.snp.bottom).offset(20)
        }

        // constrain the BOTTOM of the label 20-pts from the bottom of contentView
        bottomLabel.snp.makeConstraints { (make) in
            make.bottom.equalTo(self.contentView).offset(-20)
        }

        // with those constraints, contentView's height is now:
        // chart's height + 20 + label's height + 20
        // and because contentView's bottom is constrained to scrollView's bottom,
        // that becomes scrollView's contentSize

    }

}

我添加了一个 UILabel 作为 chart 视图，并在其下方添加了另一个标签以显示如何使用自动布局来定义滚动内容。

初始视图：

向上滚动：

以及生成的视图层次结构：

我在代码中包含的注释应该阐明这样做的方式和原因。

UIScrollView 项目不从后台移动

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