How to remove Cordova specific events outside Angular controller?

Question

Imagine I have a controller which handles, for example, view changes:

function Controller($scope){
    var viewModel = this;
    viewModel.goBack= function(){
        viewModel.visible = visibleLinks.pop(); //get last visible link 
        viewModel.swipeDirection = 'left';// for view change animation
    }
}

But I want to handle it not only for example with HTML buttons inside <body>, but also with Back button on device. So I have to add Event Listener for deviceready event, and also explicit call $scope.$apply() in order to fact, that it is called outside of AngularJS context, like this:

document.addEventListener("deviceready", function(){
        document.addEventListener("backbutton", function(){
             viewModel.goBack();
             $scope.$apply();
         }, false);
    }, false);
 }

But I also want to follow (relatively :) ) new controllerAssyntax, cause this is recommended now e.g. by Todd Motto: Opinionated AngularJS styleguide for teams and it allows to remove $scope from controllers when things like $emit or $on are not used. But I can't do it, case I have to call $apply() cause my context is not Angular context when user clicks on device back button. I thought about creating a Service which can be wrapper facade for cordova and inject $scope to this service but as I read here: Injecting $scope into an angular service function() it is not possible. I saw this: Angular JS & Phonegap back button event and accepted solution also contains $apply() which makes $scope unremovable. Anybody knows a solution to remove Cordova specific events outside Angular controller, in order to remove $scope from controllers when not explicity needed? Thank you in advance.

score 2 · Accepted Answer · answered Sep 07 '15 at 18:55

I don't see a reason why to remove the $scope from the controller. It is fine to follow the best practice and to remove it if not needed, but as you said you still need it for $emit, $on, $watch.. and you can add it $apply() in the list for sure.

What I can suggest here as an alternative solution is to implement a helper function that will handle that. We can place it in a service and use $rootScope service which is injectable.

app.factory('utilService', function ($rootScope) {

    return {
        justApply: function () {
            $rootScope.$apply();
        },
        createNgAware: function (fnCallback) {
            return function () {
                fnCallback.apply(this, arguments);
                $rootScope.$apply();
            };
        }
    };
}); 
// use it   
app.controller('SampleCtrl', function(utilService) {

    var backBtnHandler1 = function () {
        viewModel.goBack();
        utilService.justApply(); // instead of $scope.$apply();
    }
    // or
    var backBtnHandler2 = utilService.createNgAware(function(){ 
        viewModel.goBack();
    });
    document.addEventListener("backbutton", backBtnHandler2, false);
});

Michael Radionov · Answer 2 · 2015-09-08T07:49:34.453

In my case I was simply forwarding Cordova events with the help of Angular $broadcast firing it on the $rootScope. Basically any application controller would then receive this custom event. Listeners are attached on the configuration phase - in the run block, before any controller gets initialized. Here is an example:

angular
.module('app', [])
.run(function ($rootScope, $document) {

    $document.on('backbutton', function (e) {
        // block original system back button behavior for the entire application
        e.preventDefault();
        e.stopPropagation();

        // forward the event
        $rootScope.$broadcast('SYSTEM_BACKBUTTON', e);
    });

})
.controller('AppCtrl', function ($scope) {

    $scope.$on('SYSTEM_BACKBUTTON', function () {
        // do stuff
       viewModel.goBack();
    });

});

Obviously in the $scope.$on handler you do not have to call $scope.$apply().

Pros of this solution are:

you'll be able to modify an event or do something else for the entire application before the event will be broadcasted to all the controllers;
when you use $document.on() every time controller is instantiated, the event handler stays in the memory unless you manually unsibscribe from this event; using $scope.$on cares about it automatically;
if the way a system dispatches Cordova event changes, you'll have to change it in one place

Cons:

you'll have to be careful when inheriting controllers which already have an event handler attached on initialization phase, and if you want your own handler in a child.

Where to place the listeners and the forwarder is up to you and it highly depends on your application structure. If your app allows you could even keep all the logic for the backbutton event in the run block and get rid of it in controllers. Another way to organize it is to specify a single global callback attached to $rootScope for example, which can be overriden inside controllers, if they have different behavior for the back button, not to mess with events.

I am not sure about deviceready event though, it fires once in the very beginning. In my case I was first waiting for the deviceready event to fire and then was manually bootstrapping AngularJS application to provide a sequential load of the app and prevent any conflicts:

document.addEventListener('deviceready', function onDeviceReady() {
    angular.element(document).ready(function () {
        angular.bootstrap(document.body, ['app']);
    });
}, false);

From my point of view the logic of the app and how you bootstrap it should be separated from each other. That's why I've moved listener for backbutton to a run block.

How to remove Cordova specific events outside Angular controller?

2 Answers2