angular中使用了broadcast和on，为什么on里面的代码不是每次都成功运行？

var app = angular.module('gzmu', ["ngRoute",'chart.js']);
app.run(function ($rootScope, $http) {

    $http({
        method: 'GET',
        url: 'datacon/user_info.php',

    }).success(function (response) {



            $rootScope.userinfo = response[0];
        console.log($rootScope.userinfo)
        $rootScope.$broadcast("userinfo", response[0]);



    })
});
app.controller('data', function ($scope, $http, $rootScope) {
    $scope.usernamea='';
    $scope.$on("userinfo",
        function (event, msg) {
            console.log(msg);
            if(msg){
                $scope.usernamea = msg.user;
                console.log($scope.usernamea)
                alert($scope.usernamea)
            }
            else{
                alert(msg)
            }

        });
}）;

如题，on里面的代码为什么不会每加载一次页面都运行一次？