本人是作ios的之前一直用oc开发，现在摸索swift 虽然有点晚，用的oc代码转换成swift的可能存在瑕疵。欢迎提出问题一起学习进步。
上代码：
import Foundation
import UIKit
extension UIBarButtonItem{
class public func itemWithTarget(target:Any?,action:Selector,image:String,highimage:String) ->UIBarButtonItem{
let btn:UIButton = UIButton.init(type: UIButtonType.custom) btn.setBackgroundImage(UIImage.init(named: image), for: UIControlState.normal) btn.setBackgroundImage(UIImage.init(named: highimage), for: UIControlState.highlighted) var rect:CGRect = CGRect.zero
rect.size = (btn.currentBackgroundImage?.size)!
btn.frame = rect btn.addTarget(target, action: action, for: UIControlEvents.touchUpInside) return UIBarButtonItem.init(customView: btn) } }
（在控制器里）调用：（我这边定义的是返回按钮）
viewController.navigationItem.leftBarButtonItem = UIBarButtonItem.itemWithTarget(target: self, action: #selector(back), image:"返回", highimage:"ss")
@objc private func back()
{ self.popToRootViewController(animated: true); }
我写的代码不一定对，但是能运行！
