画圆角图像ios

Question

我有一个使用Core Graphics自定义绘制的按钮，我想要更改它，以便使用圆角和白色笔划圆边框绘制。我也在设置背景图片。

func imagePickerController(picker: UIImagePickerController,
    didFinishPickingMediaWithInfo info: [String : AnyObject]) {

    if  let  pickedImage  = info[UIImagePickerControllerOriginalImage] as? UIImage {

        myButton.layer.cornerRadius =  // Nothing Give me here circle
        myButton.clipsToBounds = true
        myButton.layer.borderWidth = 12.0
        myButton.layer.borderColor = UIColor.whiteColor().CGColor
        myButton.setBackgroundImage(pickedImage, forState: .Normal)
        myButton.setNeedsDisplay()
    }

    dismissViewControllerAnimated(true, completion: nil)

}

这是我申请myButton.layer.cornerRadius = myButtonrect.size.height/2

时得到的结果