Swift - UIView框架不等于UIView.layer.frame

我想绘制一个UIView图层但是当我这样做时,图层框架与UIView框架不相等(在预览中).

class ViewController: UIViewController {

    var graphHeight:CGFloat = 100
    var graphSize:CGFloat!

    override func viewDidLoad() {
        super.viewDidLoad()
        graphSize = self.view.frame.height/CGFloat(M_PI)
        let graphRect:CGRect = CGRectMake(0, graphHeight, self.view.frame.width, graphSize)
        let background = blueGardient()
        var theView:UIView = UIView(frame: graphRect)
        background.frame = theView.frame
        theView.backgroundColor = UIColor.yellowColor()
        theView.layer.cornerRadius = 8
        theView.layer.borderWidth = 1
        theView.layer.borderColor = UIColor.redColor().CGColor
        theView.layer.insertSublayer(background, atIndex: 0)
        self.view.addSubview(theView)

    }

    func blueGardient()->CAGradientLayer{
        let topColor = UIColor(red: 0, green: 0, blue: 255, alpha: 0.7)
        let bottomColor = UIColor(red: 0, green: 0, blue: 255, alpha: 0.9)
        let gradientColors: [CGColor] = [topColor.CGColor, bottomColor.CGColor]
        let gradientLocations: [Float] = [0.0, 1.0]
        let gradientLayer: CAGradientLayer = CAGradientLayer()
        gradientLayer.colors = gradientColors
        gradientLayer.locations = gradientLocations
        return gradientLayer
    }
}

框架是平等的

(0.0,100.0,320.0,180.800015352393)
(0.0,100.0,320.0,180.800015352393)

但没有显示eauql.我尝试使用theView.layer.frame但未成功...