ios - 在 Swift 中以编程方式添加约束不起作用

Question

我添加了以下代码来使以编程方式添加的 View 居中:

let horizontalConstraint = NSLayoutConstraint(item: newView!, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0)
view.addConstraint(horizontalConstraint)

这是行不通的。 View 不居中。它仍然在左边。

编辑:

    override func viewDidLoad() {
    super.viewDidLoad()

    newView = LineChartView(frame: CGRectMake(0, 0, 50, 50))
    newView?.delegate = self
    newView?.drawBordersEnabled = true
    newView?.noDataText = "No Data"
    newView?.noDataTextDescription = "No Data"
    newView?.borderColor = UIColor.blackColor()

    self.view.addSubview(newView!)

Answer 1

friend ，你需要选择一方，如果你使用自动布局，不要用frame初始化你的对象。尝试这样的事情......

var newView:LineChartView!

override func viewDidLoad() {
    super.viewDidLoad()

    newView = LineChartView()
    newView.translatesAutoresizingMaskIntoConstraints = false
    newView.delegate = self
    newView.drawBordersEnabled = true
    newView.noDataText = "No Data"
    newView.noDataTextDescription = "No Data"
    newView.borderColor = UIColor.blackColor()
    self.view.addSubview(newView)

    let width = NSLayoutConstraint(item: newView, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 50)
    let height = NSLayoutConstraint(item: newView, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 50)
    newView.addConstraint(width)
    newView.addConstraint(height)
    let x = NSLayoutConstraint(item: newView, attribute: .CenterX, relatedBy: .Equal, toItem: self.view, attribute: .CenterX, multiplier: 1, constant: 0)
    let y = NSLayoutConstraint(item: newView, attribute: .CenterY, relatedBy: .Equal, toItem: self.view, attribute: .CenterY, multiplier: 1, constant: 0)
    self.view.addConstraint(x)
    self.view.addConstraint(y)

}

如果您的 LineChartView 对象是 UIView 的子类，那么这应该有效，并且您的 super View 中间应该有一个 50x50 的对象。

如果您要在代码中进行这样的约束，您应该考虑使用 Apples Visual Formatting Language .