What's the correct way to communicate between

Question

What's the correct way to communicate between controllers?

I'm currently using a horrible fudge involving window:

function StockSubgroupCtrl($scope, $http) {
    $scope.subgroups = [];
    $scope.handleSubgroupsLoaded = function(data, status) {
        $scope.subgroups = data;
    }
    $scope.fetch = function(prod_grp) {
        $http.get('/api/stock/groups/' + prod_grp + '/subgroups/').success($scope.handleSubgroupsLoaded);
    }
    window.fetchStockSubgroups = $scope.fetch;
}

function StockGroupCtrl($scope, $http) {
    ...
    $scope.select = function(prod_grp) {
        $scope.selectedGroup = prod_grp;
        window.fetchStockSubgroups(prod_grp);
    }
}

Answer 1

Edit: The issue addressed in this answer have been resolved in angular.js version 1.2.7. $broadcast now avoids bubbling over unregistered scopes and runs just as fast as $emit.

So, now you can:

• use $broadcast from the $rootScope
• listen using $on from the local $scope that needs to know about the event

---

Original Answer Below

I highly advise not to use $rootScope.$broadcast + $scope.$on but rather $rootScope.$emit+ $rootScope.$on. The former can cause serious performance problems as raised by @numan. That is because the event will bubble down through all scopes.

However, the latter (using $rootScope.$emit + $rootScope.$on) does not suffer from this and can therefore be used as a fast communication channel!

From the angular documentation of $emit:

Dispatches an event name upwards through the scope hierarchy notifying the registered

Since there is no scope above $rootScope, there is no bubbling happening. It is totally safe to use $rootScope.$emit()/ $rootScope.$on() as an EventBus.

However, there is one gotcha when using it from within Controllers. If you directly bind to $rootScope.$on() from within a controller, you'll have to clean up the binding yourself when your local $scope gets destroyed. This is because controllers (in contrast to services) can get instantiated multiple times over the lifetime of an application which would result into bindings summing up eventually creating memory leaks all over the place :)

To unregister, just listen on your $scope's $destroy event and then call the function that was returned by $rootScope.$on.

angular
    .module('MyApp')
    .controller('MyController', ['$scope', '$rootScope', function MyController($scope, $rootScope) {

            var unbind = $rootScope.$on('someComponent.someCrazyEvent', function(){
                console.log('foo');
            });

            $scope.$on('$destroy', unbind);
        }
    ]);

I would say, that's not really an angular specific thing as it applies to other EventBus implementations as well, that you have to clean up resources.

However, you can make your life easier for those cases. For instance, you could monkey patch $rootScope and give it a $onRootScope that subscribes to events emitted on the $rootScope but also directly cleans up the handler when the local $scope gets destroyed.

The cleanest way to monkey patch the $rootScope to provide such $onRootScope method would be through a decorator (a run block will probably do it just fine as well but pssst, don't tell anybody)

To make sure the $onRootScope property doesn't show up unexpected when enumerating over $scope we use Object.defineProperty() and set enumerable to false. Keep in mind that you might need an ES5 shim.

angular
    .module('MyApp')
    .config(['$provide', function($provide){
        $provide.decorator('$rootScope', ['$delegate', function($delegate){

            Object.defineProperty($delegate.constructor.prototype, '$onRootScope', {
                value: function(name, listener){
                    var unsubscribe = $delegate.$on(name, listener);
                    this.$on('$destroy', unsubscribe);

                    return unsubscribe;
                },
                enumerable: false
            });


            return $delegate;
        }]);
    }]);

With this method in place the controller code from above can be simplified to:

angular
    .module('MyApp')
    .controller('MyController', ['$scope', function MyController($scope) {

            $scope.$onRootScope('someComponent.someCrazyEvent', function(){
                console.log('foo');
            });
        }
    ]);

So as a final outcome of all this I highly advise you to use $rootScope.$emit + $scope.$onRootScope.

Btw, I'm trying to convince the angular team to address the problem within angular core. There's a discussion going on here: https://github.com/angular/angular.js/issues/4574

Here is a jsperf that shows how much of a perf impact $broadcastbrings to the table in a decent scenario with just 100 $scope's.

http://jsperf.com/rootscope-emit-vs-rootscope-broadcast

Answer 2

Starting angular 1.5 and it's component based development focus. The recommended way for components to interact is through the use of the 'require' property and through property bindings (input/output).

A component would require another component (for instance the root component) and get a reference to it's controller:

angular.module('app').component('book', {
    bindings: {},
    require: {api: '^app'},
    template: 'Product page of the book: ES6 - The Essentials',
    controller: controller
});

You can then use the methods of the root component in your child component:

$ctrl.api.addWatchedBook('ES6 - The Essentials');

This is the root component controller function:

function addWatchedBook(bookName){

  booksWatched.push(bookName);

}

Here is a complete architectual overview: Component Communications

Answer 3

Here's the quick and dirty way.

// Add $injector as a parameter for your controller

function myAngularController($scope,$injector){

    $scope.sendorders = function(){

       // now you can use $injector to get the 
       // handle of $rootScope and broadcast to all

       $injector.get('$rootScope').$broadcast('sinkallships');

    };

}

Here is an example function to add within any of the sibling controllers:

$scope.$on('sinkallships', function() {

    alert('Sink that ship!');                       

});

and of course here's your HTML:

<button ngclick="sendorders()">Sink Enemy Ships</button>

Answer 4

Since defineProperty has browser compatibility issue, I think we can think about using a service.

angular.module('myservice', [], function($provide) {
    $provide.factory('msgBus', ['$rootScope', function($rootScope) {
        var msgBus = {};
        msgBus.emitMsg = function(msg) {
        $rootScope.$emit(msg);
        };
        msgBus.onMsg = function(msg, scope, func) {
            var unbind = $rootScope.$on(msg, func);
            scope.$on('$destroy', unbind);
        };
        return msgBus;
    }]);
});

and use it in controller like this:

• controller 1

  function($scope, msgBus) {
      $scope.sendmsg = function() {
          msgBus.emitMsg('somemsg')
      }
  }
  

• controller 2

  function($scope, msgBus) {
      msgBus.onMsg('somemsg', $scope, function() {
          // your logic
      });
  }
  

Answer 5

You can do it by using angular events that is $emit and $broadcast. As per our knowledge this is the best, efficient and effective way.

First we call a function from one controller.

var myApp = angular.module('sample', []);
myApp.controller('firstCtrl', function($scope) {
    $scope.sum = function() {
        $scope.$emit('sumTwoNumber', [1, 2]);
    };
});
myApp.controller('secondCtrl', function($scope) {
    $scope.$on('sumTwoNumber', function(e, data) {
        var sum = 0;
        for (var a = 0; a < data.length; a++) {
            sum = sum + data[a];
        }
        console.log('event working', sum);

    });
});

You can also use $rootScope in place of $scope. Use your controller accordingly.

Answer 6

The top answer here was a work around from an Angular problem which no longer exists (at least in versions >1.2.16 and "probably earlier") as @zumalifeguard has mentioned. But I'm left reading all these answers without an actual solution.

It seems to me that the answer now should be

• use $broadcast from the $rootScope
• listen using $on from the local $scope that needs to know about the event

So to publish

// EXAMPLE PUBLISHER
angular.module('test').controller('CtrlPublish', ['$rootScope', '$scope',
function ($rootScope, $scope) {

  $rootScope.$broadcast('topic', 'message');

}]);

And subscribe

// EXAMPLE SUBSCRIBER
angular.module('test').controller('ctrlSubscribe', ['$scope',
function ($scope) {

  $scope.$on('topic', function (event, arg) { 
    $scope.receiver = 'got your ' + arg;
  });

}]);

Plunkers

• Regular $scope syntax (as you see above)
• new Controller As syntax

If you register the listener on the local $scope, it will be destroyed automatically by $destroy itself when the associated controller is removed.