Question

我在Swift中创建了一个带有相应.xib文件的自定义UIView子类，但在初始化期间添加自动布局约束时遇到问题。视图本身加载得很好，但添加布局约束似乎对视图的布局没有影响，无论我是否在init或viewDidMoveToSuperview或viewDidMoveToWindow中添加这些约束，即使我之后立即致电setNeedsUpdateConstraints() / layoutIfNeeded()。

我可以在Objective-C中很容易地做到这一点，所以希望这是一个非常简单的修复，但我无法弄清楚我做错了什么。

这是我的代码：

var isLoading = false

class CustomSubview: UIView {

    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }

    private lazy var view: UIView! = { [unowned self] in
        let bundle = NSBundle(forClass: self.dynamicType)
        let nibName = String(CustomSubview.self)
        let nib = UINib(nibName: nibName, bundle: bundle)
        return nib.instantiateWithOwner(self, options: nil)[0] as! UIView
    }()

    private func setup() {
        if (isLoading) {
            return
        }

        isLoading = true
//        self.view.frame = self.bounds // this works but I want to use Auto Layout
//        self.view.autoresizingMask = [UIViewAutoresizing.FlexibleWidth, UIViewAutoresizing.FlexibleHeight] // this works but I want to use Auto Layout
        self.translatesAutoresizingMaskIntoConstraints = false // no effect
        addSubview(self.view)
        let views = Dictionary(dictionaryLiteral: ("view", self.view))
        let horizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat("H:|[view]|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views)
        self.addConstraints(horizontalConstraints)
        NSLayoutConstraint.activateConstraints(horizontalConstraints) // this seems to do nothing
        let verticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat("V:|[view]|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views)
        self.addConstraints(verticalConstraints)
        NSLayoutConstraint.activateConstraints(verticalConstraints) // this seems to do nothing
        self.setNeedsUpdateConstraints()
        self.layoutIfNeeded()
        isLoading = false
    }

}

Answer 1

我重新修改了你的课程，使它看起来更清洁。我省略了加载Bool。此外，我没有从XIB文件创建视图的经验，我几乎没有触及它。

var isLoading = false

class CustomSubview: UIView {

    override init(frame: CGRect) {
        super.init(frame: frame)

        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        setup()
    }

    private lazy var customView: UIView = {
        let bundle = NSBundle(forClass: self.dynamicType)
        let nibName = String(CustomSubview.self)
        let nib = UINib(nibName: nibName, bundle: bundle)
        let customView = nib.instantiateWithOwner(self, options: nil)[0] as! UIView
        customView.translatesAutoresizingMaskIntoConstraints = false

        return customView
    }()

    private func setup() {
        if (isLoading) {
            return
        }

        isLoading = true
        addSubview(self.customView)
        let views = ["customView": customView]

        addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[customView]|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views))
        addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[customView]|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views))
        isLoading = false
    }
}

对于宽高比约束，您可以为宽高比设置多个约束，并将active的{{1}}设置为true / false以在它们之间切换。

无法以编程方式在Swift中添加NSLayoutConstraints（无效）

1 个答案: