UI 从代码创建的不会显示

Question

我正在尝试从代码创建用户界面。这是代码：

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let superview = self.view

        let myLabel = UILabel()
        myLabel.setTranslatesAutoresizingMaskIntoConstraints(false)
        myLabel.text = "My Label"

        let myButton = UIButton()
        myButton.setTitle("My Button", forState: UIControlState.Normal)
        myButton.backgroundColor = UIColor.blueColor()
        myButton.setTranslatesAutoresizingMaskIntoConstraints(false)
        superview.addSubview(myLabel)
        superview.addSubview(myButton)

        var myConstraint=NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: superview, attribute: NSLayoutAttribute.CenterY, multiplier: 1.0, constant: 0)
        superview.addConstraint(myConstraint)

        myConstraint=NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: myButton, attribute: NSLayoutAttribute.CenterX, multiplier: 1.0, constant: 0)
        superview.addConstraint(myConstraint)

        myConstraint=NSLayoutConstraint(item: myButton, attribute: NSLayoutAttribute.Trailing, relatedBy: NSLayoutRelation.Equal, toItem: myLabel, attribute: NSLayoutAttribute.Leading, multiplier: 1.0, constant: -10)
        superview.addConstraint(myConstraint)

        myConstraint=NSLayoutConstraint(item: myButton, attribute: NSLayoutAttribute.Baseline, relatedBy: NSLayoutRelation.Equal, toItem: myLabel, attribute: NSLayoutAttribute.Baseline, multiplier: 1.0, constant: 0)
        superview.addConstraint(myConstraint)

    }

根据我正在阅读的书籍教程，这段代码应该创建一个按钮和一个标签。当我运行模拟器没有任何显示（空白模拟器）。你能帮我找出错误吗？

Answer 1

你的第三个约束

myConstraint=NSLayoutConstraint(item: myButton, attribute: NSLayoutAttribute.Trailing, relatedBy: NSLayoutRelation.Equal, toItem: myLabel, attribute: NSLayoutAttribute.Leading, multiplier: 1.0, constant: -10)

尝试并排放置标签和按钮。

你的第二个约束

myConstraint=NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: myButton, attribute: NSLayoutAttribute.CenterX, multiplier: 1.0, constant: 0)

尝试将它们一个放在另一个上面。

这两个约束之一将不得不取消！

UI 从代码创建的不会显示

UI created from code won't show up

user-interface

swift

ios8