设置 constraint.isActive = true 时抛出错误

Question

我有一个 scrollView，我要在其中添加一个 textView。我想将文本视图置于 schollView 的中心。该代码在行 textView.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor, constant: 0).isActive = true 上抛出错误，但仅当我也调用 .isActive = true 时才会抛出错误。

@IBOutlet weak var scrollView: UIScrollView!

override func viewDidLoad() {
    super.viewDidLoad()

    let textView = UITextView(frame: CGRect(x: 0, y: 0, width: 200, height: 1000))
    textView = text
    textView.translatesAutoresizingMaskIntoConstraints = false
    textView.sizeToFit()
    textView.isScrollEnabled = false

    scrollView.translatesAutoresizingMaskIntoConstraints = false
    textView.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor, constant: 0).isActive = true
}

我错过了什么？

Answer 1

你需要添加它

scrollView.addSubview(textView)
textView.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor, constant: 0).isActive = true

在设置约束之前，如果你在IB里面设置了scrollview的约束，那就不要设置

// comment scrollView.translatesAutoresizingMaskIntoConstraints = false

设置 constraint.isActive = true 时抛出错误

Error thrown when set constraint.isActive = true

constraints

nslayoutconstraint

swift