更改导航栏按钮项的标题

let button = UIButton()
        button.setImage(UIImage(named: "coin_icon"), forState: UIControlState.Normal)
        button.addTarget(self, action:#selector(Profile.goCoin), forControlEvents: UIControlEvents.TouchDragInside)
        button.frame=CGRectMake(0, 0, 30, 30)
        let barButton = UIBarButtonItem(customView: button)
        self.navigationItem.rightBarButtonItem = barButton
let button = UIButton()
        button.setImage