swift-导航栏添加自定义返回按钮

//1.添加返回按钮

    func addBackBtn(){

       let leftBtn:UIBarButtonItem=UIBarButtonItem(title: "返回", style: UIBarButtonItemStyle.Plain, target: self, action: "actionBack")

        leftBtn.title="返回";

        leftBtn.tintColor=UIColor.whiteColor();

        self.navigationItem.leftBarButtonItem=leftBtn;

    }

    //返回按钮事件

    func actionBack(){

        self.navigationController?.popToRootViewControllerAnimated(true);

    }