Constraints programmatically for custom UIView in Dynamic ViewController - ios

Question

I'm creating new UIViewController dynamycally using this code
#IBAction func newVCBtnPressed(_ sender: Any) {
let controller = DynamicVC()
show(controller, sender: sender)
}
In the new UIViewController I'm using this code for creation of the new UIView:
override func loadView() {
view = UIView()
view.backgroundColor = .lightGray
}
In result I have view with .lightGray backgroundcolor.
I want to add custom UIView and setup the constraints programmatically, and in result i want UIView with following constraints:
top: 0
bottom:(view.frame.height*0.9)
leading:0
trailing:(view.frame.width*0.15)
width:(view.frame.width*0.85)
height:(view.frame.height*0.1)
Example:
Here is my code:
topMenuView = UIView()
topMenuView.backgroundColor = .red
view.addSubview(topMenuView)
topMenuView.translatesAutoresizingMaskIntoConstraints = false
setupConstraints(item: topMenuView, topC: 0, topToItem: view, bottomC: (view.frame.height*0.9), bottomToItem: view, widthC: (view.frame.width*0.85), heightC: (view.frame.height*0.1), leadingCon: 0, trailingCon: (view.frame.width*0.15))
I'm using this constructed function for constraints:
func setupConstraints(item:UIView, topC:CGFloat, topToItem:UIView, bottomC:CGFloat, bottomToItem:UIView, widthC:CGFloat, heightC:CGFloat, leadingCon:CGFloat, trailingCon:CGFloat) {
let topConstraint = NSLayoutConstraint(item: item, attribute: .top, relatedBy: .equal, toItem: topToItem, attribute: .bottom, multiplier: 1, constant: topC)
let bottomConstraint = NSLayoutConstraint(item: item, attribute: .bottom, relatedBy: .equal, toItem: bottomToItem, attribute: .top, multiplier: 1, constant: bottomC)
let widthConstraint = NSLayoutConstraint(item: item, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: widthC)
let heightConstraint = NSLayoutConstraint(item: item, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: heightC)
let leading = NSLayoutConstraint(item: item,attribute: .leading,relatedBy: .equal, toItem: view, attribute: .leadingMargin, multiplier: 1.0, constant: leadingCon)
let trailing = NSLayoutConstraint(item: item,attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailingMargin,multiplier: 1.0,constant: trailingCon)
view?.addConstraints([topConstraint, bottomConstraint, widthConstraint, heightConstraint, leading, trailing])
NSLayoutConstraint.activate([topConstraint, bottomConstraint, widthConstraint, heightConstraint, leading, trailing])
}
But in the result i receive only UIView with gray background, the new UIView with red background doesn't appears.
What I'm doing wrong???

Answer 1

You should only specify bottom OR height and width OR trailing, otherwise you are going to get conflicts here.
see playground:
import PlaygroundSupport
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let red = UIView()
red.backgroundColor = .red
view.addSubview(red)
red.translatesAutoresizingMaskIntoConstraints = false
red.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
red.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
red.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.85).isActive = true
red.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.1).isActive = true
}
}
PlaygroundPage.current.liveView = ViewController()