swift -自定义返回图片，替换系统图片

 /// 设置返回图片
    func setNavBackBtn(backType:JYBackBtnTypeEnum){
        var imageName = ""
        switch backType {
        case JYBackBtnTypeEnum.gray:
            imageName = "back_normal_gray"
        case JYBackBtnTypeEnum.white:
            imageName = "back_normal_white"
        }
        let item = UIBarButtonItem(image:  UIImage.init(named: imageName)?.withRenderingMode(UIImage.RenderingMode.alwaysOriginal), style: .plain, target: self, action: #selector(clcikBackBtn))
        self.navigationItem.leftBarButtonItems = [item]
    }
    
    //返回按钮点击响应
    @objc func clcikBackBtn(){
        self.navigationController?.popViewController(animated: true)
    }