intrinsicContentSize titleView的自动居中

    override var intrinsicContentSize: CGSize {
        //如果是这种的话，titleView的left和right会顶到leftBartButtonItem和rightBarButtonItem
        //        return UIView.layoutFittingExpandedSize

        return CGSize(width: 150, height: IPHONE_NAVIGATIONBAR_HEIGHT - IPHONE_STATUSBAR_HEIGHT)
        
    }