利用构造函数设置导航栏

给 UIBarButtonItem 添加扩展类UIBarButtonItem-Extension

import UIKit

extension UIBarButtonItem {
    /*
    class func createItem(imageName : String, highImageName : String, size : CGSize) -> UIBarButtonItem {
        let btn = UIButton()
        
        btn.setImage(UIImage(named: imageName), forState: .Normal)
        btn.setImage(UIImage(named: highImageName), forState: .Highlighted)
        
        btn.frame = CGRect(origin: CGPointZero, size: size)
        
        return UIBarButtonItem(customView: btn)
    }
    */
    
    // 便利构造函数: 1> convenience开头 2> 在构造函数中必须明确调用一个设计的构造函数(self)
    convenience init(imageName : String, highImageName : String = "", size : CGSize = CGSize.zero)  {
        // 1.创建UIButton
        let btn = UIButton()
        
        // 2.设置btn的图片
        btn.setImage(UIImage(named: imageName), for: UIControlState())
        if highImageName != "" {
            btn.setImage(UIImage(named: highImageName), for: .highlighted)
        }
        
        // 3.设置btn的尺寸
        if size == CGSize.zero {
            btn.sizeToFit()
        } else {
            btn.frame = CGRect(origin: CGPoint.zero, size: size)
        }
        
        // 4.创建UIBarButtonItem
        self.init(customView : btn)
    }
}

然后在控制器中创建自定义 item

   fileprivate func setupNavigationBar() {
        // 1.设置左侧的Item
        navigationItem.leftBarButtonItem = UIBarButtonItem(imageName: "logo")
        
        // 2.设置右侧的Item
        let size = CGSize(width: 40, height: 40)
        let historyItem = UIBarButtonItem(imageName: "image_my_history", highImageName: "Image_my_history_click", size: size)
        let searchItem = UIBarButtonItem(imageName: "btn_search", highImageName: "btn_search_clicked", size: size)
        let qrcodeItem = UIBarButtonItem(imageName: "Image_scan", highImageName: "Image_scan_click", size: size)
        navigationItem.rightBarButtonItems = [historyItem, searchItem, qrcodeItem]
    }