xcode – IBDesignable UIButton子类

我正在尝试实现一个IBDesignable的简单UIButton子类.我希望能够从Interface Builder为控件的每个状态设置颜色.我知道这可以通过IBInspectable关键字实现.我在状态属性上使用KVO时遇到IB崩溃问题. IBDesignable调试器在deinit上崩溃.有谁知道我如何与KVO和IBDesignable一起工作？

@IBDesignable
class UIButtonActionButton: UIButton {

    @IBInspectable var defaultColour: UIColor = UIColor.blueColor() {
        didSet {
            self.setNeedsdisplay()
        } 
    }

    @IBInspectable var selectedColour: UIColor = UIColor.blueColor()

    @IBInspectable var disabledColour: UIColor = UIColor.grayColor()

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

    override init(frame: CGRect) {
        super.init(frame: frame)
        self._setup()
    }


    private func _setup(){
        self.addobserver(self,forKeyPath: "state",options: NSkeyvalueObservingOptions.New,context: nil)
        self.layer.cornerRadius = 5.0
        self.layer.masksToBounds = true
    }

    override func observeValueForKeyPath(keyPath: String,ofObject object: AnyObject,change: [NSObject : AnyObject],context: UnsafeMutablePointer<Void>) {
        self.setNeedsdisplay()
    }

    override func drawRect(rect: CGRect) {
        super.drawRect(rect)
        let context = UIGraphicsGetCurrentContext()

        if self.highlighted {
            CGContextSetFillColorWithColor(context,selectedColour.CGColor)
            CGContextFillRect(context,self.bounds)
        } else if self.state == UIControlState.disabled {
            CGContextSetFillColorWithColor(context,disabledColour.CGColor)
            CGContextFillRect(context,self.bounds)
        } else {
            CGContextSetFillColorWithColor(context,defaultColour.CGColor)
            CGContextFillRect(context,self.bounds)
        }
    }

    deinit {
        self.removeObserver(self,context: nil)
    }

}

#if !TARGET_INTERFACE_BUILDER
required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    self._setup()
}
#endif

override func prepareForInterfaceBuilder() {
    self._setup()
}