如何在ios swift中以编程方式创建自动布局等宽约束？

Question

How to give programmatically constraints equal width and equal height with multiple views.I check google but not perfect answer for programmatically equal width and height constraints through auto layout.

my code look like below:

  var countNoOfViews:Int = 3   
 @IBOutlet var viewForRow1: UIView!

override func viewDidLoad() {
        super.viewDidLoad()
 self.specialButtonViewLeft()
}

func specialButtonViewLeft(){

    for i in 0..<countNoOfViews{
        var customView:UIView!
        customView = UIView(frame: CGRect.zero)
        customView.translatesAutoresizingMaskIntoConstraints = false
        viewForRow1.addSubview(customView)

        let widthConstraint = NSLayoutConstraint(item: customView, attribute: .width, relatedBy: .equal,toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 20.0)

        let topConstraint = NSLayoutConstraint(item: customView, attribute: .top, relatedBy: .equal,toItem: self.viewForRow1, attribute: .top, multiplier: 1.0, constant: 0)

        let bottomConstraint = NSLayoutConstraint(item: customView, attribute: .bottom, relatedBy: .equal,toItem: self.viewForRow1, attribute: .bottom, multiplier: 1.0, constant: 0)

        let leadingConstraint = NSLayoutConstraint(item: customView, attribute: .leading, relatedBy: .equal, toItem: self.viewForRow1, attribute: .leading, multiplier: 1, constant: customLeadingSpaceLeft)

        customLeadingSpaceLeft = customLeadingSpaceLeft + customViewWidth

        arrayLeftBtnConstraints.append(widthConstraint)

        if i == 0{
            customView.backgroundColor = UIColor.red
        }else if i == 1{
            customView.backgroundColor = UIColor.green
        }else if i == 2{
            leftViewVal = customLeadingSpaceLeft
            customView.backgroundColor = UIColor.black
        }
        customView.alpha = 0.50
        viewForRow1.addConstraints([widthConstraint, leadingConstraint,topConstraint,bottomConstraint])
    }
}

I want to add equal width constraint programmatically.

Answer 1

You have three possible ways to do that:

1) By using anchors:

view.widthAnchor.constraint(equalTo: otherView.widthAnchor, multiplier: 1.0).isActive = true

2) Visual format:

simple example - "H:|[otherView]-[view(==otherView)]|"

3) "Old school" constraints:

NSLayoutConstraint(item: #view, attribute: .width, relatedBy: .equal, toItem: #otherView, attribute: .width, multiplier: 1.0, constant: 0.0).isActive = true

hope it will help somebody.

Answer 2

Try this:

let widthConstraint = NSLayoutConstraint(item: customView, attribute: .width, relatedBy: .equal, toItem: viewForRow1, attribute: .width, multiplier: 0.25, constant: 0.0)

multiplier: 0.25 , denotes that customView 's width will be 1/4th of the parent view, viewForRow1 .