感谢Steve的提示，我得以实现加载程序：

拦截器：

.factory('httpInterceptor', function ($q, $rootScope, $log) {

    var numLoadings = 0;

    return {
        request: function (config) {

            numLoadings++;

            // Show loader
            $rootScope.$broadcast("loader_show");
            return config || $q.when(config)

        },
        response: function (response) {

            if ((--numLoadings) === 0) {
                // Hide loader
                $rootScope.$broadcast("loader_hide");
            }

            return response || $q.when(response);

        },
        responseError: function (response) {

            if (!(--numLoadings)) {
                // Hide loader
                $rootScope.$broadcast("loader_hide");
            }

            return $q.reject(response);
        }
    };
})
.config(function ($httpProvider) {
    $httpProvider.interceptors.push('httpInterceptor');
});

指示：

.directive("loader", function ($rootScope) {
    return function ($scope, element, attrs) {
        $scope.$on("loader_show", function () {
            return element.show();
        });
        return $scope.$on("loader_hide", function () {
            return element.hide();
        });
    };
}
)

CSS：

#loaderDiv {
   position: fixed;
   top: 0;
   right: 0;
   bottom: 0;
   left: 0;
   z-index: 1100;
   background-color: white;
   opacity: .6;
}

.ajax-loader {
   position: absolute;
   left: 50%;
   top: 50%;
   margin-left: -32px; /* -1 * image width / 2 */
   margin-top: -32px; /* -1 * image height / 2 */
   display: block;
}

HTML：

<div id="loaderDiv" loader>
    <img src="src/assets/img/ajax_loader.gif" class="ajax-loader"/>
</div>