AngularJS trigger and watch object value change in service from controller - angularjs

Question

I'm trying to watch for changes in a service from a controller. I tried various things based on many qns here on stackoverflow, but I've been unable to make it work.
html:
<div ng-app="myApp">
<div ng-controller="MyCtrl">
<div ng-click="setFTag()">Click Me</div>
</div>
</div>
javascript:
var myApp = angular.module('myApp',[]);
myApp.service('myService', function() {
this.tags = {
a: true,
b: true
};
this.setFalseTag = function() {
alert("Within myService->setFalseTag");
this.tags.a = false;
this.tags.b = false;
//how do I get the watch in MyCtrl to be triggered?
};
});
myApp.controller('MyCtrl', function($scope, myService) {
$scope.setFTag = function() {
alert("Within MyCtrl->setFTag");
myService.setFalseTag();
};
$scope.$watch(myService.tags, function(newVal, oldVal) {
alert("Inside watch");
console.log(newVal);
console.log(oldVal);
}, true);
});
How do I get the watch to trigger in the Controller?
jsfiddle

Answer 1

Try to write $watch by this way:
myApp.controller('MyCtrl', function($scope, myService) {
$scope.setFTag = function() {
myService.setFalseTag();
};
$scope.$watch(function () {
return myService.tags;
},
function(newVal, oldVal) {
/*...*/
}, true);
});
Demo Fiddle
[EDIT]
Sometimes this way will not work especially if service has been updated from 3d party.
To make it work we must help to angular to fire digest cycle.
Here is an example:
On service side when we want update tags value write something like:
if($rootScope.$root.$$phase != '$apply' && $rootScope.$root.$$phase != '$digest'){
$rootScope.$apply(function() {
self.tags = true;
});
}
else {
self.tags = true;
}