How to add a border just on the top side of a UIView

My question is on the title.

I don't know how to add a border in a specific side, top or bottom, any side... layer.border draws the border for the whole view...

Solution 1:

I consider subclassing UIView and overriding drawRect overkill here. Why not add an extension on UIView and add border subviews?

@discardableResult
func addBorders(edges: UIRectEdge,
                color: UIColor,
                inset: CGFloat = 0.0,
                thickness: CGFloat = 1.0) -> [UIView] {

    var borders = [UIView]()

    @discardableResult
    func addBorder(formats: String...) -> UIView {
        let border = UIView(frame: .zero)
        border.backgroundColor = color
        border.translatesAutoresizingMaskIntoConstraints = false
        addSubview(border)
        addConstraints(formats.flatMap {
            NSLayoutConstraint.constraints(withVisualFormat: $0,
                                           options: [],
                                           metrics: ["inset": inset, "thickness": thickness],
                                           views: ["border": border]) })
        borders.append(border)
        return border
    }


    if edges.contains(.top) || edges.contains(.all) {
        addBorder(formats: "V:|-0-[border(==thickness)]", "H:|-inset-[border]-inset-|")
    }

    if edges.contains(.bottom) || edges.contains(.all) {
        addBorder(formats: "V:[border(==thickness)]-0-|", "H:|-inset-[border]-inset-|")
    }

    if edges.contains(.left) || edges.contains(.all) {
        addBorder(formats: "V:|-inset-[border]-inset-|", "H:|-0-[border(==thickness)]")
    }

    if edges.contains(.right) || edges.contains(.all) {
        addBorder(formats: "V:|-inset-[border]-inset-|", "H:[border(==thickness)]-0-|")
    }

    return borders
}

    // Usage:         
    view.addBorder(edges: [.all]) // All with default arguments 
    view.addBorder(edges: [.top], color: .green) // Just Top, green, default thickness
    view.addBorder(edges: [.left, .right, .bottom], color: .red, thickness: 3) // All except Top, red, thickness 3

With this code you're not tied to your subclass too, you can apply it to anything and everything that inherits from UIView - reusable in your project, and any others. Pass in other arguments to your methods to define other colours and widths. Many options.

Solution 2:

Added capability for rounded corners to Adam Waite's original post, and the multiple edits

Important!: Don't forgot to add 'label.layoutIfNeeded()' right before calling 'addborder' as previously commented

Note: I've only tested this on UILabels.

extension CALayer {
    
    enum BorderSide {
        case top
        case right
        case bottom
        case left
        case notRight
        case notLeft
        case topAndBottom
        case all
    }
    
    enum Corner {
        case topLeft
        case topRight
        case bottomLeft
        case bottomRight
    }
    
    func addBorder(side: BorderSide, thickness: CGFloat, color: CGColor, maskedCorners: CACornerMask? = nil) {
        var topWidth = frame.size.width; var bottomWidth = topWidth
        var leftHeight = frame.size.height; var rightHeight = leftHeight
        
        var topXOffset: CGFloat = 0; var bottomXOffset: CGFloat = 0
        var leftYOffset: CGFloat = 0; var rightYOffset: CGFloat = 0
        
        // Draw the corners and set side offsets
        switch maskedCorners {
        case [.layerMinXMinYCorner, .layerMaxXMinYCorner]: // Top only
            addCorner(.topLeft, thickness: thickness, color: color)
            addCorner(.topRight, thickness: thickness, color: color)
            topWidth -= cornerRadius*2
            leftHeight -= cornerRadius; rightHeight -= cornerRadius
            topXOffset = cornerRadius; leftYOffset = cornerRadius; rightYOffset = cornerRadius
            
        case [.layerMinXMaxYCorner, .layerMaxXMaxYCorner]: // Bottom only
            addCorner(.bottomLeft, thickness: thickness, color: color)
            addCorner(.bottomRight, thickness: thickness, color: color)
            bottomWidth -= cornerRadius*2
            leftHeight -= cornerRadius; rightHeight -= cornerRadius
            bottomXOffset = cornerRadius
            
        case [.layerMinXMinYCorner, .layerMinXMaxYCorner]: // Left only
            addCorner(.topLeft, thickness: thickness, color: color)
            addCorner(.bottomLeft, thickness: thickness, color: color)
            topWidth -= cornerRadius; bottomWidth -= cornerRadius
            leftHeight -= cornerRadius*2
            leftYOffset = cornerRadius; topXOffset = cornerRadius; bottomXOffset = cornerRadius;
            
        case [.layerMaxXMinYCorner, .layerMaxXMaxYCorner]: // Right only
            addCorner(.topRight, thickness: thickness, color: color)
            addCorner(.bottomRight, thickness: thickness, color: color)
            topWidth -= cornerRadius; bottomWidth -= cornerRadius
            rightHeight -= cornerRadius*2
            rightYOffset = cornerRadius
            
        case [.layerMaxXMinYCorner, .layerMaxXMaxYCorner,  // All
              .layerMinXMaxYCorner, .layerMinXMinYCorner]:
            addCorner(.topLeft, thickness: thickness, color: color)
            addCorner(.topRight, thickness: thickness, color: color)
            addCorner(.bottomLeft, thickness: thickness, color: color)
            addCorner(.bottomRight, thickness: thickness, color: color)
            topWidth -= cornerRadius*2; bottomWidth -= cornerRadius*2
            topXOffset = cornerRadius; bottomXOffset = cornerRadius
            leftHeight -= cornerRadius*2; rightHeight -= cornerRadius*2
            leftYOffset = cornerRadius; rightYOffset = cornerRadius
            
        default: break
        }
        
        // Draw the sides
        switch side {
        case .top:
            addLine(x: topXOffset, y: 0, width: topWidth, height: thickness, color: color)
            
        case .right:
            addLine(x: frame.size.width - thickness, y: rightYOffset, width: thickness, height: rightHeight, color: color)
            
        case .bottom:
            addLine(x: bottomXOffset, y: frame.size.height - thickness, width: bottomWidth, height: thickness, color: color)
            
        case .left:
            addLine(x: 0, y: leftYOffset, width: thickness, height: leftHeight, color: color)

        // Multiple Sides
        case .notRight:
            addLine(x: topXOffset, y: 0, width: topWidth, height: thickness, color: color)
            addLine(x: 0, y: leftYOffset, width: thickness, height: leftHeight, color: color)
            addLine(x: bottomXOffset, y: frame.size.height - thickness, width: bottomWidth, height: thickness, color: color)

        case .notLeft:
            addLine(x: topXOffset, y: 0, width: topWidth, height: thickness, color: color)
            addLine(x: frame.size.width - thickness, y: rightYOffset, width: thickness, height: rightHeight, color: color)
            addLine(x: bottomXOffset, y: frame.size.height - thickness, width: bottomWidth, height: thickness, color: color)

        case .topAndBottom:
            addLine(x: topXOffset, y: 0, width: topWidth, height: thickness, color: color)
            addLine(x: bottomXOffset, y: frame.size.height - thickness, width: bottomWidth, height: thickness, color: color)

        case .all:
            addLine(x: topXOffset, y: 0, width: topWidth, height: thickness, color: color)
            addLine(x: frame.size.width - thickness, y: rightYOffset, width: thickness, height: rightHeight, color: color)
            addLine(x: bottomXOffset, y: frame.size.height - thickness, width: bottomWidth, height: thickness, color: color)
            addLine(x: 0, y: leftYOffset, width: thickness, height: leftHeight, color: color)
        }
    }
    
    private func addLine(x: CGFloat, y: CGFloat, width: CGFloat, height: CGFloat, color: CGColor) {
        let border = CALayer()
        border.frame = CGRect(x: x, y: y, width: width, height: height)
        border.backgroundColor = color
        addSublayer(border)
    }
    
    private func addCorner(_ corner: Corner, thickness: CGFloat, color: CGColor) {
        // Set default to top left
        let width = frame.size.width; let height = frame.size.height
        var x = cornerRadius
        var y = cornerRadius
        var startAngle: CGFloat = .pi; var endAngle: CGFloat = .pi*3/2
        
        switch corner {
        case .bottomLeft:
            y = height - cornerRadius 
            startAngle = .pi/2; endAngle = .pi
            
        case .bottomRight:
            x = width - cornerRadius
            y = height - cornerRadius
            startAngle = 0; endAngle = .pi/2
            
        case .topRight:
            x = width - cornerRadius
            startAngle = .pi*3/2; endAngle = 0
            
        default: break
        }
        
        let cornerPath = UIBezierPath(arcCenter: CGPoint(x: x, y: y),
                                      radius: cornerRadius - thickness,
                                      startAngle: startAngle,
                                      endAngle: endAngle,
                                      clockwise: true)

        let cornerShape = CAShapeLayer()
        cornerShape.path = cornerPath.cgPath
        cornerShape.lineWidth = thickness
        cornerShape.strokeColor = color
        cornerShape.fillColor = nil
        addSublayer(cornerShape)
    }
}