影つきの UIButton のサブクラスです。

ShadowedButton.swift

class ShadowedButton : UIButton {
    override func willMoveToSuperview(newSuperview: UIView?) {
        super.willMoveToSuperview(newSuperview)
        
        self.addTarget(self, action: #selector(addShadow), forControlEvents: UIControlEvents.TouchDown)
        self.addTarget(self, action: #selector(addShadow), forControlEvents: UIControlEvents.TouchDragEnter)
        
        self.addTarget(self, action: #selector(removeShadow), forControlEvents: UIControlEvents.TouchDragExit)
        self.addTarget(self, action: #selector(removeShadow), forControlEvents: UIControlEvents.TouchUpInside)
    }
    
    func addShadow(){
        self.backgroundColor = UIColor(white: 0.0, alpha: 0.1)
    }
    
    func removeShadow(){
        self.backgroundColor = UIColor.clearColor()
    }
    
    override func removeFromSuperview() {
        super.removeFromSuperview()
    }
}