ios Swift 3 以编程方式创建 UILabel 并添加 NSLayoutConstraints
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Swift 3 Create UILabel programmatically and add NSLayoutConstraints
提问by iGeorge
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:
您好，我正在尝试以编程方式创建一个标签并添加 NSLayoutConstraints，以便无论屏幕大小和方向等如何，它都可以在超级视图中居中。我已经看过了，但找不到可以遵循的示例。这是我所拥有的：
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)
回答by Josh Homann
NSLayoutAnchorwas new in iOS 9 and it greatly cleans up the constraint syntax.
NSLayoutAnchor是 iOS 9 中的新功能，它极大地清理了约束语法。
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
self.contentView.addSubview(codedLabel)
codedLabel.translatesAutoresizingMaskIntoConstraints = false
codedLabel.heightAnchor.constraint(equalToConstant: 200).isActive = true
codedLabel.widthAnchor.constraint(equalToConstant: 200).isActive = true
codedLabel.centerXAnchor.constraint(equalTo: codedLabel.superview!.centerXAnchor).isActive = true
codedLabel.centerYAnchor.constraint(equalTo: codedLabel.superview!.centerYAnchor).isActive = true
回答by Rajat
See below code as an example
以下面的代码为例
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])
回答by Huy Nguyen
let myLabel: UILabel = {
let lb = UILabel()
lb.translatesAutoresizingMaskIntoConstraints = false
lb.textAlignment = .center
lb.numberOfLines = 1
lb.textColor = UIColor.black
lb.font=UIFont.systemFont(ofSize: 22)
lb.backgroundColor = UIColor.grey
return lb
}()
In super.viewDidLoad()method, You need add label to your view and
add contraints for the label:
在super.viewDidLoad()方法中，您需要向视图添加标签并为标签添加约束：
override func viewDidLoad() {
super.viewDidLoad()
self.view.addSubView(myLabel)
setUpMyLabel()
}
func setUpMyLabel() {
NSLayoutConstraint.activate([
myLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
myLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor),
myLabel.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.7),
myLabel.heightAnchor.constraint(equalToConstant: 50)])
}
I hope the my code can help to you.
我希望我的代码可以对您有所帮助。
