I have event listeners activated by:
var unregisterSubscription = $rootScope.$on(event, handler);
The event is activated in component and/or directive.
I want the listener to listen when the user uses the scope of the listener, otherwise not.
now my question is where i activate the unregisterSubscription method?
You can create destroy event in controller.
$rootScope.$on('$destroy', function() {
unregisterSubscription(); // Call unregisterSubscription method.
});
Related
So I have this situation where one controller is emitting the event and the other controller has the listener. Here is the code:
In controller A, I have this method:
$scope.process = function () {
var taskName = 'process';
$scope.$emit('process', taskName);
}
In controller B, I have this:
$rootScope.$on('process', function (event, taskName) {
//Do something here
});
Now whenever I visit other pages on application and comeback to this, the process listener gets created twice. I cannot use controller scope as the event is getting emitted from other controller. How can I destroy listener once it has completed its task? I have also tried $scope.$destroy(). Doesn't really work. What is the correct way of doing this?
I am on Angularjs 1.4.7.
Usually you do it in different way:
$rootScope.$broadcast(...)
...
$scope.$on(...)
Then you do not need to unsubscribe.
If you really need for some reason to subscribe to $rootScope, then:
var deregister = $scope.$on(...);
...
deregister(); // destory that listener
I want to prevent $scope.$destroy event in my nested controller in my page. I see the event object in callback function has method preventDefault, but it's not working as I expect.
$scope.$on('$destroy', function(event) {
event.preventDefault(); // don't working!
});
It is possible to prevent $destroy event?
plnkr Example
Can you listen for $destroy globally? i.e. When any controller is destroyed not just the current controller.
You can use the broadcast
$scope.$broadcast('destroy');
and listen it wherever you want, like this
$scope.$on('destroy', function (event, data) {
// do whatever you want to do
});
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.
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);
});
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 $rootScope for example, which can be overriden inside controllers, if they have different behavior for the back button, not to mess with events.
I am not sure about deviceready event though, it fires once in the very beginning. In my case I was first waiting for the deviceready event to fire and then was manually bootstrapping AngularJS application to provide a sequential load of the app and prevent any conflicts:
document.addEventListener('deviceready', function onDeviceReady() {
angular.element(document).ready(function () {
angular.bootstrap(document.body, ['app']);
});
}, false);
From my point of view the logic of the app and how you bootstrap it should be separated from each other. That's why I've moved listener for backbutton to a run block.
I saw a piece of code in a controller recently that went something like:
.controller('foobar', ['$scope', '$rootScope', function($scope, $rootScope) {
var eventHandler = $rootScope.$on('some-event', function() {
...
});
// remove eventHandler
$scope.$on('$destroy', eventHandler);
}]);
Questions:
Is executing the eventHandler "deregistration" function on $scope's $destroy event necessary?
If yes, would executing the deregistration function on $scope's $destroy event have been necessary if 'some-event' was $on $scope instead of $rootScope?
How do I know when I need to execute a deregistration function? I understand detaching or unbinding events is common for cleanup in JavaScript, but what rules can I follow to know when to do this in Angular?
Any advice about understanding this snippet/"deregistration" would be much appreciated.
In the example above the destroy method is necessary. The listener is bound to the $rootscope which means that even after the controller gets $destroy-ed the listener is still attached to the dom through the $rootscope. Every time the controller is instantiated a new eventhandler will be created so without the destroy method you will have a memory leak.
However if you bind the listener to the controllers $scope it will get destroyed along with the controller as the $scope gets destroyed so the listener has no connection to the dom thus making it eligible for garbage collection
Event handlers are only deregistered on controller's $destroy event when it is on that controller's $scope.
The deregistering would be unnecessary if it's on $scope since that's handled for you by Angular.
Generally if it's not tied to instance of the individual element, controller, or service you are listening on then that is when you need to handle deregistering yourself.
A good example is a directive that registers event listeners on the $document:
var module = angular.module('test', []);
module.directive('onDocumentClick', function directiveFactory($document) {
return {
link: function (scope, element, attrs) {
var onDocumentClick = function () {
console.log('document clicked')
};
$document.on('click', onDocumentClick);
// we need to deregister onDocumentClick because the event listener is on the $document not the directive's element
element.on('$destroy', function () {
$document.off('click', onDocumentClick);
});
}
};
});