在swift中设置UIBarButtonItem的背景图像

我正在尝试以编程方式设置UIBarButtonItem的背景图像.但我的图像被拉伸和平铺.任何帮助解决这个问题将非常感激.这是我的代码

var objectSelected : UIImage!{
    didSet{
        if objectSelected == nil {
            objectSelected = UIImage(named: "line")
        }
       let insets = UIEdgeInsetsMake(0, 0, 10, 0)
        objectSelected.resizableImageWithCapInsets(insets)
      objectSelector.setBackgroundImage(objectSelected, forState: UIControlState.Normal, style: UIBarButtonItemStyle.Plain, barMetrics: UIBarMetrics.Default)

    }
}


@IBOutlet weak var objectSelector: UIBarButtonItem!

你可以试试这个.

var myBtn: UIButton = UIButton()
    myBtn.setImage(UIImage(named: "line"), forState: .Normal)
    myBtn.frame = CGRectMake(0, 0, 70, 70)
    myBtn.addTarget(self, action: "myBtnAction:", forControlEvents: .TouchUpInside)

    self.navigationItem.setLeftBarButtonItem(UIBarButtonItem(customView: myBtn), animated: true)