Pressable flat button

PressableButton.swift

//
//  PressableButton.swift
//
//  Created by clmntcrl on 19/08/2014.
//  Copyright (c) 2014 clmntcrl. All rights reserved.
//


import UIKit


private let _defaultShadowColor = UIColor.blackColor()
private let _defaultShadowOffset = CGSize(width: 2.0, height: 4.0)


class PressableButton: UIButton {

    var pressed = false
    var shadowColor: UIColor {
        get { return UIColor(CGColor: layer.shadowColor) }
        set { layer.shadowColor = newValue.CGColor }
    }
    var shadowOffset: CGSize {
        get { return layer.shadowOffset }
        set { layer.shadowOffset = newValue }
    }
    private var _shadowOffset = CGSizeZero

    override var enabled: Bool {
        didSet { _stateChange() }
    }
    override var highlighted: Bool {
        didSet { _stateChange() }
    }
    override var selected: Bool {
        didSet { _stateChange() }
    }


    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        _makeItPressable()
    }

    private func _makeItPressable() {
        shadowColor = _defaultShadowColor
        shadowOffset = _defaultShadowOffset

        layer.shadowOpacity = 1.0
        layer.shadowRadius = 0.0
    }

    private func _stateChange() {
        if state == .Highlighted {
            if !pressed {
                pressed = true

                _shadowOffset = shadowOffset
                shadowOffset.width = (-1.0...1.0).contains(_shadowOffset.width) ? 0.0 : (_shadowOffset.width.isSignMinus ? -1.0 : 1.0)
                shadowOffset.height = (-1.0...1.0).contains(_shadowOffset.height) ? 0.0 : (_shadowOffset.height.isSignMinus ? -1.0 : 1.0)
                transform.tx = _shadowOffset.width - shadowOffset.width
                transform.ty = _shadowOffset.height - shadowOffset.height
            }
        } else {
            if pressed {
                pressed = false

                shadowOffset = _shadowOffset
                transform.tx = 0.0
                transform.ty = 0.0
            }
        }
    }

}