在 Swift 3 中以编程方式使用 ScrollView

问题描述

我搜索了其他问题，但似乎在使用 swift 3 中的自动布局以编程方式创建我的滚动视图时仍然遇到一些问题.我能够让我的滚动视图显示如下图所示，但是当我滚动到底部时，我的其他标签不会出现，滚动顶部"标签不会消失.

I have searched other questions and seem to still have some trouble creating my scrollView programmatically with autolayout in swift 3. I am able to get my scrollview to show up as shown in the picture below, but when I scroll to the bottom my other label does not show up and the 'scroll top' label does not disappear.

希望有人可以帮助查看我下面的代码！

Hoping someone can help review my code below!

import UIKit

class ViewController: UIViewController {

let labelOne: UILabel = {
    let label = UILabel()
    label.text = "Scroll Top"
    label.backgroundColor = .red
    label.translatesAutoresizingMaskIntoConstraints = false
    return label
}()

let labelTwo: UILabel = {
    let label = UILabel()
    label.text = "Scroll Bottom"
    label.backgroundColor = .green
    label.translatesAutoresizingMaskIntoConstraints = false
    return label
}()


override func viewDidLoad() {
    super.viewDidLoad()

    let screensize: CGRect = UIScreen.main.bounds
    let screenWidth = screensize.width
    let screenHeight = screensize.height
    var scrollView: UIScrollView!
    scrollView = UIScrollView(frame: CGRect(x: 0, y: 120, width: screenWidth, height: screenHeight))
    scrollView.contentSize = CGSize(width: screenWidth, height: 2000)
    scrollView.addSubview(labelOne)
    scrollView.addSubview(labelTwo)


    view.addSubview(labelOne)
    view.addSubview(labelTwo)
    view.addSubview(scrollView)

    // Visual Format Constraints
    view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0": labelOne]))
    view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-100-[v0]", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0": labelOne]))

    // Using iOS 9 Constraints in order to place the label past the iPhone 7 view
    view.addConstraint(NSLayoutConstraint(item: labelTwo, attribute: .top, relatedBy: .equal, toItem: labelOne, attribute: .bottom, multiplier: 1, constant: screenHeight + 200))
    view.addConstraint(NSLayoutConstraint(item: labelTwo, attribute: .right, relatedBy: .equal, toItem: labelOne, attribute: .right, multiplier: 1, constant: 0))
    view.addConstraint(NSLayoutConstraint(item: labelTwo, attribute: .left, relatedBy: .equal, toItem: labelOne, attribute: .left, multiplier: 1, constant: 0)

    }

}

推荐答案

很容易使用约束来定义滚动内容的大小 - 因此您无需进行任何手动计算.

It is easy to use constraints to define the scroll content size - so you don't have to do any manual calculations.

记住:

1. 滚动视图的内容元素必须具有左/上/宽/高值.对于标签等对象，它们具有固有大小，因此您只需定义 left &顶.
2. 滚动视图的内容元素还定义了可滚动区域的边界 - contentSize -但他们这样做的底部 &正确的约束.
3. 结合这两个概念，您会发现您需要一个连续链"，其中至少有一个元素定义了顶部/左侧/底部/右侧范围.

1. The content elements of your scroll view must have left / top / width / height values. In the case of objects such as labels, they have intrinsic sizes, so you only have to define the left & top.
2. The content elements of your scroll view also define the bounds of the scrollable area - the contentSize - but they do so with the bottom & right constraints.
3. Combining those two concepts, you see that you need a "continuous chain" with at least one element defining the top / left / bottom / right extents.

这是一个简单的例子，它将直接在 Playground 页面中运行:

Here is a simple example, that will run directly in a Playground page:

import UIKit
import PlaygroundSupport

class TestViewController : UIViewController {

    let labelOne: UILabel = {
        let label = UILabel()
        label.text = "Scroll Top"
        label.backgroundColor = .red
        label.translatesAutoresizingMaskIntoConstraints = false
        return label
    }()

    let labelTwo: UILabel = {
        let label = UILabel()
        label.text = "Scroll Bottom"
        label.backgroundColor = .green
        label.translatesAutoresizingMaskIntoConstraints = false
        return label
    }()

    let scrollView: UIScrollView = {
        let v = UIScrollView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = .cyan
        return v
    }()


    override func viewDidLoad() {
        super.viewDidLoad()

        // add the scroll view to self.view
        self.view.addSubview(scrollView)

        // constrain the scroll view to 8-pts on each side
        scrollView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 8.0).isActive = true
        scrollView.topAnchor.constraint(equalTo: view.topAnchor, constant: 8.0).isActive = true
        scrollView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -8.0).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -8.0).isActive = true

        // add labelOne to the scroll view
        scrollView.addSubview(labelOne)

        // constrain labelOne to left & top with 16-pts padding
        // this also defines the left & top of the scroll content
        labelOne.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 16.0).isActive = true
        labelOne.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 16.0).isActive = true

        // add labelTwo to the scroll view
        scrollView.addSubview(labelTwo)

        // constrain labelTwo at 400-pts from the left
        labelTwo.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 400.0).isActive = true

        // constrain labelTwo at 1000-pts from the top
        labelTwo.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 1000).isActive = true

        // constrain labelTwo to right & bottom with 16-pts padding
        labelTwo.rightAnchor.constraint(equalTo: scrollView.rightAnchor, constant: -16.0).isActive = true
        labelTwo.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: -16.0).isActive = true

    }

}


let vc = TestViewController()
vc.view.backgroundColor = .yellow
PlaygroundPage.current.liveView = vc

这篇关于在 Swift 3 中以编程方式使用 ScrollView的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！