Extension UIView to add borders in partnership with @diegoventura and @brunogb

Playground.swift

import UIKit
import PlaygroundSupport

extension UIView {
    private class UIViewNamed: UIView {
        var name: String
        var thickness: CGFloat? = nil
        required init(frame: CGRect = CGRect.zero, name: String) {
            self.name = name
            
            super.init(frame: frame)
        }
        
        required init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
    }
    
    public enum RectEdge: String {
        case top
        case right
        case bottom
        case left
    }

    open func set(to edge: RectEdge, with color: UIColor, thickness: CGFloat? = nil) {
        let view = self.border(to: edge) ?? UIViewNamed(name: edge.rawValue)
        let thicknessToApply = thickness ?? view.thickness ?? 1.0
        
        view.backgroundColor = color
        view.translatesAutoresizingMaskIntoConstraints = false
        view.thickness = thicknessToApply
        
        self.removeConstraints(view.constraints)
        self.addSubview(view)
        self.constraint(to: view, edge: edge, thickness: thicknessToApply)
    }
    
    private func border(to edge: RectEdge) -> UIViewNamed? {
        let index = self.subviews.index(where: {
            if $0 is UIViewNamed, let view = $0 as? UIViewNamed, view.name == edge.rawValue {
                return true
            }
            
            return false
        })
        
        guard let i = index else {
            return nil
        }
        
        return self.subviews[i] as? UIViewNamed
    }
    
    private func constraint(to view: UIView, edge: RectEdge, thickness: CGFloat) {
        
        switch edge {
        case .top:
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-(0)-[top(==thickness)]",
                                                               options: [],
                                                               metrics: ["thickness": thickness],
                                                               views: ["top": view]))
            
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-(0)-[top]-(0)-|",
                                                               options: [],
                                                               metrics: nil,
                                                               views: ["top": view]))
            break
            
        case .right:
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:[right(==thickness)]-(0)-|",
                                                               options: [],
                                                               metrics: ["thickness": thickness],
                                                               views: ["right": view]))
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-(0)-[right]-(0)-|",
                                                               options: [],
                                                               metrics: nil,
                                                               views: ["right": view]))
            break
            
        case .bottom:
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:[bottom(==thickness)]-(0)-|",
                                                               options: [],
                                                               metrics: ["thickness": thickness],
                                                               views: ["bottom": view]))
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-(0)-[bottom]-(0)-|",
                                                               options: [],
                                                               metrics: nil,
                                                               views: ["bottom": view]))
            break
            
        case .left:
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-(0)-[left(==thickness)]",
                                                               options: [],
                                                               metrics: ["thickness": thickness],
                                                               views: ["left": view]))
            self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-(0)-[left]-(0)-|",
                                                               options: [],
                                                               metrics: nil,
                                                               views: ["left": view]))
            break
        }
    }
}



class ViewController : UIViewController {
    
    var sub: UIView?
    
    func more() {
        var frame = sub?.frame
        frame?.size.height += 25
        
        sub?.frame = frame!
    }
    
    func less() {
        var frame = sub?.frame
        frame?.size.height -= 25
        
        sub?.frame = frame!
    }
    
    override func loadView() {
        let view = UIView()
        
        
        let more = UIButton(frame: CGRect(x: 135, y: 120, width: 40, height: 20))
        more.setTitle("+", for: .normal)
        more.addTarget(self, action: #selector(self.more), for: .touchUpInside)
        more.backgroundColor = .gray
        view.addSubview(more)
        
        let less = UIButton(frame: CGRect(x: more.frame.maxX + 10, y: more.frame.minY, width: 40, height: 20))
        less.setTitle("-", for: .normal)
        less.addTarget(self, action: #selector(self.less), for: .touchUpInside)
        less.backgroundColor = .lightGray
        view.addSubview(less)
        
        sub = UIView(frame: CGRect(x: more.frame.minX, y: more.frame.maxY + 10, width: 90, height: 50))
        sub?.backgroundColor = .green
        sub?.set(to: .bottom, with: UIColor.gray, thickness: 5)
        
        
        view.addSubview(sub!)
        view.backgroundColor = UIColor.white
        self.view = view
    }
    
}

PlaygroundPage.current.liveView = ViewController()

We can change the UIViewNamed, and add a thickness attribute:

private class UIViewNamed: UIView {
        var name: String
        var thickness: CGFloat? = nil
        required init(frame: CGRect = CGRect.zero, name: String) {
            self.name = name
            
            super.init(frame: frame)
        }
        
        required init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
    }

and then on method set(border: we can change it to:

open func set(border edge: RectEdge, with color: UIColor, thickness: CGFloat? = nil) {
        let view = self.border(to: edge) ?? UIViewNamed(name: edge.rawValue)
        let thicknessToApply = thickness ?? view.thickness ?? 1.0
        view.backgroundColor = color
        view.translatesAutoresizingMaskIntoConstraints = false
        view.thickness = thicknessToApply
        self.removeConstraints(view.constraints)
        self.addSubview(view)
        self.constraint(to: view, edge: edge, thickness: thicknessToApply)
    }

what do you think?