Input value can't refresh when type new value in modal

The problem is when type new value with input in ionicModal, the $scope value is not refresh

the code

controller

$scope.username = null;
$scope.password = null;
$scope.login = function(u,p){

      var data = {
          username:u,
          password:p
      }

      $http.post('http://localhost:1337/login',data)
      .success(function(data, status, headers,config){
          console.log(data);
          $scope.modal.hide();
      })
      .error(function(data, status, headers,config){

          var alertPopup = $ionicPopup.alert({
                  title: '登陆错误!',
                 template: data.error,
                 buttons:[
                     {
                         "text":"确认",
                         "type":"button-assertive"
                     }
                 ]
               });
      });

  }

$scope.username and $scope.password is bind to input, but they are not refresh when type new value,

For example, input value is ‘aaaa’, but $scope.username was still null, I guess the scope in ionicModal was the copy of parentScope, so scope value in ionicModal is refresh, but parentScope is not refresh