Communicating between controllers in AngularJS

I have seen many solutions to how to make controllers talk to each other whilst at the same time remaining within "da rulez" of writing Angular applications.
I have been using Angular for about a month now and at times it has been swearier than a good Haskell session, it is most definitely worth it all in the end. I have written a really nice looking web application for my employer and they seem to like it. I think Angular.
One thing I really aced (to my own satisfaction at least) was wrapping a REST (of any type) API using a resource. I will make a separate post about that.

Do the simplest thing...

Here is my own solution to the problem of how you can make different controllers communicate cleanly using the "event" system that Angular provides. All you have to do is ensure that the following event listener is added to your application root-scope:

App.run( function( $rootScope )) {
    $rootScope.$on('broadcast', function( e, data ) {
        if (undefined == data.with) {
            $rootScope.$broadcast(data.say);
        }
        else {
            $rootScope.$broadcast(data.say, data.with);
        }
    });
});

There is of course a calling convention now but it is very very simple indeed and should not cause any undue hardship. It allows any normal data to be passed around, here is the format of the object that you must pass as the only argument

    {
        say: 'message-identifier',
        with: message-data (optional)
    }

How it does what it does...

If you read the (improving) documentation closely you will know that $emit() ripples messages up the scope hierarchy and $broadcast goes the other way. As we have added this to the root-scope it means that when the message arrives and is re-dispatched, it's going to go back down to every scope that is currently alive and listening. And that is how we achieve the seemingly impossible task of leaping between branches of a tree, which is essentially what communicating between controllers is all about.

Using it, an example...

I am currently writing a stop-motion web application so I can make the next block-buster Lego animation film. I use Linux and having used what appears to be the only Linux stop-motion program available ("stopmotion") and having found it to be a little unstable and buggy at times I did what any self-respecting hacker would do (next to fixing those bugs!), which is "roll your own".
I have a window that shows the video from the camera and a "configure" button that replaces the camera image with a configuration dialog in the same space. My issue was how to tell the rest of the UI that the user had toggled a checkbox, because the state of the checkbox had to cause the UI to make some changes.
All I had to do with my simplest-thing-possible broadcast helper was send an event like this:
[code] $scope.toggleIPCam = function() { $scope.isIPCam = !$scope.isIPCam; $scope.$emit('broadcast', { say: 'IPCamMode', with: $scope.isIPCam }); }; }; [code] Don't forget that the value for with can be any valid data type, the example shows a boolean being passed but it could as easily have been a function or an object etc.
Here is how we catch it and deal with it...

    $scope.$on('IPCamMode', function(ev, mode) {
        console.log("received mode change on camera: "+mode);
        $scope.isIPCam = mode;
    });

How difficult is that? And remember that if you didn't pass any data then you can dispense with having to declare anything at all after the event parameter and of course, if you don't care about the event then you don't need any formal parameters at all!
So there you have it, inter-controller communications in one simple addition to $rootScope at the cost of following a very simple calling convention.
Hope that helps fellow AngularJS jockeys everywhere.