angularjs - Do I need an apply in a $scope.$on? -

i`m using angular 1.4.

i have watchgroup in scope:

    $scope.$watchgroup(         ["scroll_top", "tokeninput_has_focus"],         function(newvalues, oldvalues, scope) {             console.log("watch");                 }     ); 

and change $scope.scroll_top variable in event:

out of scope function:

restegourmetapp.directive("scroll", function ($window) {     return function(scope, element, attrs) {         angular.element($window).bind("scroll", function() {             scope.$broadcast("onwindowscroll", $window);         });     }; }); 

inside scope function:

    $scope.$on('onwindowscroll', function(scope, element, attrs) {          $scope.scroll_top = $window.scrolly;         console.log("scroll");     }); 

but watchgroup function not executed, when scroll, console outputs "scroll" not "watch".

i need change

    $scope.$on('onwindowscroll', function(scope, element, attrs) {          $scope.scroll_top = $window.scrolly;         $scope.$apply();         console.log("scroll");     }); 

to trigger watch function-

i not understand this? thought inside scope $scope.$on.

there must not understand, can me?

thank you!