Swift iOS8 drawRect在操场奇怪的碰撞

我有一个很好的条形图类，在一个应用程序中使用我自己的核心图形代码，在操场上玩的时候，我注意到drawRect似乎被称为很多次，当什么都没有改变的时候，我在下面缩写了我的代码，但要点如下

我注意到，如果我将axis绘图代码放在一个方法中，然后调用该方法，则Playerd会运行drawRect数千次，直到程序崩溃。如果我知道它是如何显示在下面，它只运行一次

class BarGraphView: UIView {

    var frameWidth = CGFloat(0.0)
    var frameHeight = CGFloat(0.0)
    var values = [CGFloat]()
    var maxY = CGFloat(0.0)
    var title = NSString(string: "")
    var xLabel = NSString(string: "")

    let gridOffSetY = CGFloat(0.1)

    var xaxis : CGFloat {
        return 0.6*frameWidth
    }
    var yaxis : CGFloat {
    return 0.6*frameWidth
    }
    var xstart : CGFloat {
    return 0.2*frameWidth
    }
    var ystart : CGFloat {
    return 0.3*frameWidth
    }

    var xseparation: CGFloat {
        return CGFloat(xaxis*0.05)
    }

    init(frame: CGRect, data: [CGFloat], maxYVal: Int, title: String, xLabel: String) {
        super.init(frame: frame)
        frameWidth = frame.width
        frameHeight = frame.height
        values = data
        maxY = CGFloat(maxYVal)
        self.title = title as NSString
        self.xLabel = xLabel as NSString
    }
    override func drawRect(rect: CGRect) {

        let numValues = CGFloat(values.count)

        let context = UIGraphicsGetCurrentContext()

        CGContextSetFillColorWithColor(context, UIColor.whiteColor().CGColor);
        CGContextFillRect(context, bounds);

        CGContextSetFillColorWithColor(context, UIColor.greenColor().CGColor)

        let barWidth:CGFloat = ((xaxis-(numValues+1)*xseparation)/numValues)
        var count:CGFloat = 0
        for number in values {
            let x = xstart + xseparation + (count * (barWidth + xseparation))
            let barRect = CGRect(x: x, y:ystart+yaxis, width: barWidth, height: -(number/maxY)*yaxis)
            CGContextAddRect(context, barRect)
            count++
        }
        CGContextFillPath(context)

        // IF THIS CODE IS HERE, IT IS RUN ONCE IN PLAYGROUND

        // Axis Drawing
        var bezier = UIBezierPath()

        // Draw y-axis
        bezier.moveToPoint(CGPointMake(xstart,ystart))
        bezier.addLineToPoint(CGPointMake(xstart,ystart+yaxis+5))

        // Draw x-axis
        bezier.moveToPoint(CGPointMake(xstart-5,ystart+yaxis))
        bezier.addLineToPoint(CGPointMake(xstart+xaxis,ystart+yaxis))

        // Draw value markings on y-axis
        let divisor = CGFloat((yaxis-gridOffSetY)/maxY) // max y-value, with offset
        for i in 1..<maxY {
            bezier.moveToPoint(CGPointMake(xstart-CGFloat(2.5),ystart+gridOffSetY+CGFloat(i)*divisor))
            bezier.addLineToPoint(CGPointMake(xstart,ystart+gridOffSetY+CGFloat(i)*divisor))
        }
        UIColor.blackColor().setStroke()
        bezier.stroke()

       // IF PUT THAT ^ in this method, it runs thousands of times consecutively, crashing Xcode.
       //drawAxis()
    }

这看起来像是潜在的童车行为，是游乐场的怪异行为，还是对此有任何合乎逻辑的解释