登陆成功后，跳转到主页面，需要隐藏后退回登陆页面的按钮

let vc:UIViewController=self.storyboard?.instantiateViewControllerWithIdentifier("view name") as!UIViewController

//先隐藏回退按钮，然后push 否则无效

vc.navigationItem.hidesBackButton=true

self.navigationController?.pushViewController(vc,animated:true)