ios - 向 TextView 添加约束在 Swift 中不起作用

Question

我使用的是 XCode 6.1，我正在尝试向 TextView 添加约束。我已经通过将这些代码行添加到我的 ViewController 的 viewDidLoad() 函数中成功地完成了它:

    myButton.backgroundColor = UIColor.orangeColor()
    myButton.setTitle("New test old button", forState: .Normal)
    self.view.addSubview(myButton)
    myButton.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.view.addConstraint(NSLayoutConstraint(item: myButton, attribute: .Leading, relatedBy: .Equal, toItem: self.view, attribute: .Leading, multiplier: 1.0, constant: 20.0))
    self.view.addConstraint(NSLayoutConstraint(item: myButton, attribute: .Top, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1.0, constant: 200.0))

但是当我尝试对 TextView 执行相同操作时，我无法在 iOS 模拟器的屏幕上看到它:

    var textView = UITextView(frame: CGRect(x: 100, y: 100, width: 300, height: 300))
    textView.text = "My test text!"
    textView.sizeToFit()
    textView.backgroundColor = UIColor.purpleColor()
    self.view.addSubview(textView)
    textView.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.view.addConstraint(NSLayoutConstraint(item: textView, attribute: .Leading, relatedBy: .Equal, toItem: self.view, attribute: .Leading, multiplier: 1.0, constant: 10.0))
    self.view.addConstraint(NSLayoutConstraint(item: textView, attribute: .Top, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1.0, constant: 400.0))

如果我要删除三个约束特定行，则会创建 TextView，但我需要这些约束才能正确格式化所有内容。

有人知道我做错了什么吗？

Answer 1

您需要为 TextView 的宽度和高度添加约束:

self.view.addConstraint(NSLayoutConstraint(item: textView, attribute: .Width, relatedBy: .Equal,
   toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 300.0))

self.view.addConstraint(NSLayoutConstraint(item: textView, attribute: .Height, relatedBy: .Equal,
    toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 300.0))