Swift - 修改导航栏返回Button的Title

A push B

在 A 页面的 viewWillDisappear

   override func viewWillDisappear(_ animated: Bool)
   {
       super.viewWillDisappear(animated)

       let backItem = UIBarButtonItem()
       backItem.title = ""
       self.navigationItem.backBarButtonItem = backItem 
   }