function login(){
     if(!empty($_POST)){
         //验证码校验
         $verify = new \Think\Verify();
         if(!$verify->check($_POST['captcha'])){
             echo "验证码错误";
         } else {
             //判断用户名和密码,在model模型里边制作一个专门方法进行验证
             $user = new \Model\ManagerModel();
             $rst = $user -> checkNamePwd($_POST['mg_username'],$_POST['mg_password']);
             if($rst === false){
                 echo "用户名或密码错误";
             } else {
                 //登录信息持久化$_SESSION
                 session('mg_username',$rst['mg_name']);
                 session('mg_id',$rst['mg_id']);
                 //$this ->redirect($url, $params, $delay, $msg)
                 //$this -> redirect('Index/index',array('id'=>100,'name'=>'tom'),2,'用户马上登陆到后台');
                 $this -> redirect('Index/index');
             }
         }
     } 
     $this -> assign('lang',L());
     $this -> display();
 }