swift - UIScrollView 显示 subview 不正确

Question

我试图在 ScrollView 中显示简单的自定义 View 。这是我的代码:

struct scrollViewDataStruct {
    let title: String?
    let image: UIImage?
}

class ViewController: UIViewController {
     @IBOutlet weak var scrollView: UIScrollView!

     var scrollViewData = [scrollViewDataStruct]()

     override func viewDidLoad() {
         super.viewDidLoad()
         scrollViewData = [
         scrollViewDataStruct(title: "First", image: #imageLiteral(resourceName: "iPhone 8 Copy 2")),
        scrollViewDataStruct(title: "Second", image: #imageLiteral(resourceName: "iPhone 8 Copy 3"))
    ]
    self.scrollView.backgroundColor = .yellow
    scrollView.contentSize.width = self.scrollView.frame.width * CGFloat(scrollViewData.count)
    var i = 0
    for _ in scrollViewData {
        let view = CustomView(frame: CGRect(x: self.scrollView.frame.width * CGFloat(i), y: 0, width: scrollView.frame.width, height: self.scrollView.frame.height))
        self.scrollView.addSubview(view)
        i += 1
    }
    // Do any additional setup after loading the view, typically from a nib.
}

}

class CustomView: UIView {

let imageView: UIImageView = {
   let imageView = UIImageView()
    imageView.translatesAutoresizingMaskIntoConstraints = false
    imageView.backgroundColor = UIColor.blue
    return imageView
}()

override init(frame: CGRect) {
    super.init(frame: frame)
    self.addSubview(imageView)
    imageView.leftAnchor.constraint(equalTo: self.leftAnchor).isActive = true
    imageView.rightAnchor.constraint(equalTo: self.rightAnchor).isActive = true
    imageView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
    imageView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}    
}

如您所见，CustomView 的框架=scrollView 的框架，但是当我运行应用程序时，它并不像我预期的那样:

然后，在 Storyboard中，我将设备从 iphone8 更改为 iphone 8 plus 并再次运行。它正确显示 CustomView 。我不知道， scrollView 总是正确的，但 CustomView 不是。有什么建议吗？

Answer 1

您的问题是，在自动布局运行并确定 ScrollView 的frame的大小之前，您正在访问scrollView的frame实际设备。快速解决方法是将您的设置代码移至 viewDidLayoutSubviews 的重写中。但您必须小心，因为与 viewDidLoad 不同，viewDidLayoutSubviews 将运行多次，因此您必须确保不会多次添加 View 。

// property - have we set up the views yet?
var setup = false

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    if !setup {
        scrollView.contentSize.width = self.scrollView.frame.width * CGFloat(scrollViewData.count)
        var i = 0
        for _ in scrollViewData {
            let view = CustomView(frame: CGRect(x: self.scrollView.frame.width * CGFloat(i), y: 0, width: scrollView.frame.width, height: self.scrollView.frame.height))
            self.scrollView.addSubview(view)
            i += 1
        }
        setup = true
    }
}

您应该考虑使用约束将 View 放置在scrollView内容中，而不是扰乱frame计算，然后自动布局会自动做正确的事情。