Question

我试图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)

    }

根据我以下的书籍教程，此代码应创建一个Button和一个Label。当我运行模拟器时，没有任何显示（空白模拟器）。你能帮我找到错误吗？

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)

尝试将标签和按钮并排放置。

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)

试图将它们放在另一个之上。

这两个限制中的一个必须要去！

从代码创建的UI不会显示

1 个答案: