XcodeのLive Renderingを使って簡単に使い勝手の良いアイコンボタンをつくろう ref: http://qiita.com/morizotter/items/3483108f8e3266ef4c81

file0.txt

@IBDesignable
class IconButton: UIControl {

    @IBInspectable var iconImage: UIImage?

    override func drawRect(rect: CGRect) {

        if let iconImage = self.iconImage {
            iconImage.drawInRect(self.bounds)

            let maskPath = UIBezierPath(roundedRect: self.bounds, cornerRadius: CGRectGetWidth(self.bounds) / 2)
            let maskLayer = CAShapeLayer()
            maskLayer.path = maskPath.CGPath
            self.layer.mask = maskLayer;
        }
    }
}

file1.txt

@IBDesignable
class IconButton: UIControl {

    @IBInspectable var iconImage: UIImage?
    @IBInspectable var borderColor: UIColor = UIColor.clearColor()
    @IBInspectable var lineWidth: CGFloat = 0.0
    var borderLayer: CAShapeLayer?

    override func drawRect(rect: CGRect) {

        if let iconImage = self.iconImage {
            iconImage.drawInRect(self.bounds)
        }

        let path = UIBezierPath(roundedRect: self.bounds, cornerRadius: CGRectGetWidth(self.bounds) / 2)
        let maskLayer = CAShapeLayer()
        maskLayer.path = path.CGPath
        self.layer.mask = maskLayer;

        if self.borderLayer == nil {
            self.borderLayer = CAShapeLayer()
            self.borderLayer!.path = path.CGPath
            self.borderLayer!.fillColor = UIColor.clearColor().CGColor
            self.layer.addSublayer(self.borderLayer!)
        }
        self.borderLayer!.strokeColor = self.borderColor.CGColor
        self.borderLayer!.lineWidth = self.lineWidth
        self.borderLayer!.lineCap = kCALineCapRound
    }
}

file2.txt

@IBDesignable
class IconButton: UIControl {

    @IBInspectable var normalImage: UIImage? {
        didSet {
            self.setNeedsDisplay()
        }
    }

    @IBInspectable var highlightedImage: UIImage? {
        didSet {
            self.setNeedsDisplay()
        }
    }

    @IBInspectable var normalBorderColor: UIColor = UIColor.clearColor() {
        didSet {
            self.setNeedsDisplay()
        }
    }

    @IBInspectable var highlightedBorderColor: UIColor = UIColor.clearColor() {
        didSet {
            self.setNeedsDisplay()
        }
    }

    @IBInspectable var lineWidth: CGFloat = 0.0 {
        didSet {
            self.setNeedsDisplay()
        }
    }

    lazy var maskLayer: CAShapeLayer = {
        return CAShapeLayer()
    }()

    lazy var borderLayer: CAShapeLayer = {
        let borderLayer = CAShapeLayer()
        borderLayer.fillColor = UIColor.clearColor().CGColor
        self.layer.addSublayer(borderLayer)
        return borderLayer
    }()

    var circlePath: UIBezierPath {
        get {
            return UIBezierPath(roundedRect: self.bounds, cornerRadius: CGRectGetWidth(self.bounds) / 2)
        }
    }

    override var highlighted: Bool {
        didSet {
            self.setNeedsDisplay()
        }
    }

    override func drawRect(rect: CGRect) {

        var iconImage: UIImage?
        var borderColor = UIColor.clearColor()
        if self.highlighted {
            if let highlightedImage = self.highlightedImage {
                iconImage = highlightedImage
                borderColor = self.highlightedBorderColor
            }
        } else {
            if let normalImage = self.normalImage {
                iconImage = normalImage
                borderColor = self.normalBorderColor
            }
        }

        iconImage?.drawInRect(self.bounds)

        self.maskLayer.path = self.circlePath.CGPath
        self.layer.mask = self.maskLayer

        self.borderLayer.path = self.circlePath.CGPath
        self.borderLayer.strokeColor = borderColor.CGColor
        self.borderLayer.lineWidth = self.lineWidth
    }
}

file3.txt

import UIKit

class ViewController: UIViewController {

    @IBAction func buttonTapped(sender: IconButton) {
        println("button tapped!")
    }
}