Swift 3以编程方式创建UILabel并添加NSLayoutConstraints

问题描述

您好我正在尝试以编程方式创建标签并添加NSLayoutConstraints，使其在superview中居中，无论屏幕大小和方向等等。我看过但是找不到示例。以下是我的内容：

Hello I am trying to create a label programmatically and add NSLayoutConstraints so that it is centered in the superview regardless of screen size and orientation etc. I have looked but just can't find an example to follow. Here is what I have:

let codedLabel:UILabel = UILabel()
codedLabel.frame = CGRect(x: 100, y: 100, width: 200, height: 200)
codedLabel.textAlignment = .center
codedLabel.text = alertText
codedLabel.numberOfLines=1
codedLabel.textColor=UIColor.red
codedLabel.font=UIFont.systemFont(ofSize: 22)
codedLabel.backgroundColor=UIColor.lightGray

let heightConstraint:NSLayoutConstraint = NSLayoutConstraint(item: codedLabel, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 200)

let widthConstraint:NSLayoutConstraint = NSLayoutConstraint(item: codedLabel, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 200)

codedLabel.addConstraints([heightConstraint, widthConstraint])

let verticalConstraint:NSLayoutConstraint = NSLayoutConstraint(item: codedLabel, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: self.contentView, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0)

let horizontalConstraint:NSLayoutConstraint = NSLayoutConstraint(item: codedLabel, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: self.contentView, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0)

self.contentView.addConstraints([verticalConstraint, horizontalConstraint])

self.contentView.addSubview(codedLabel)

推荐答案

见下面的代码作为例子

let lblNew = UILabel()
lblNew.backgroundColor = UIColor.blue
lblNew.text = "Test"
lblNew.textColor = UIColor.white
lblNew.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(lblNew)

let widthConstraint = NSLayoutConstraint(item: lblNew, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 300)
let heightConstraint = NSLayoutConstraint(item: lblNew, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 200)
var constraints = NSLayoutConstraint.constraints(
    withVisualFormat: "V:[superview]-(<=1)-[label]",
    options: NSLayoutFormatOptions.alignAllCenterX,
    metrics: nil,
    views: ["superview":view, "label":lblNew])

view.addConstraints(constraints)

// Center vertically
constraints = NSLayoutConstraint.constraints(
    withVisualFormat: "H:[superview]-(<=1)-[label]",
    options: NSLayoutFormatOptions.alignAllCenterY,
    metrics: nil,
    views: ["superview":view, "label":lblNew])

view.addConstraints(constraints)

view.addConstraints([ widthConstraint, heightConstraint])

这篇关于Swift 3以编程方式创建UILabel并添加NSLayoutConstraints的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！