AngularJS – Non-nested Directive-to-Directive Communication – Code Example

• What is Directive-to-Directive Communication?
• Service Helps Directives Communicate
• Code Example – Non-nested Directives Communication

What is Directive-to-Directive Communication?

When the change in one or more attributes of one directive need to trigger one or more events in other directives resulting in updating of their attributes and related view, this can be termed as directive-to-directive communication. I, recently, open-sourced an Angular QuizApp which demonstrates the non-nested directive-to-directive communication. In the QuizApp, there are two directives, namely, iquestion and iscorecard. As one answers a question (iquestion directive), the score gets updated and displayed as part of iscorecard directive. Take a look at live example on following page: ATG Platform – Test 1

Service Helps Directives Communicate

As the directives are non-nested, meaning not placed within each other, it presents challenge on how to have them communicate with each other. With nested directives, controllers within directives define APIs that are used to communicate with each other. With non-nested directives, one can have them communicate using following method:

• Define an object that consists of attributes whose change can trigger one or more event.
• Define an Angular service that returns the above object using “factory” recipe method.
• Inject the service into directives which needs to communicate.
• Within directives, watch for change in the service attributes using scope.$watch API and take appropriate action.

Code Example – Non-nested Directives Communication

Pay attention to some of the following in the code example below:

• helloservice defined using “factory” recipe method
• helloservice injected into hello and bye directives
• scope.$watch API used to watch change in name attribute of the service and assign the value to name attribute

angular.module('HelloModule', [])
.directive( 'hello', function( helloservice) {
	return {
		restrict: "E",
		scope:{
			name: '@'
		},
		controller: function( $scope, helloservice ) {
			$scope.updateName = function() {
			  helloservice.setName( $scope.name );
			};
		},
		link: function( scope, element, attrs ) {
		  helloservice.setName( scope.name );
		},
		templateUrl: '/assets/templates/hello1.html'
	}
})
.directive( 'bye', function( helloservice ) {
	return {
		restrict: "E",
		scope:{			
		},
		controller: function( $scope, helloservice ) {
		  $scope.name = helloservice.getName();  
		},
		link: function( scope, element, attrs ) {
		  scope.$watch(function() {
				return helloservice.name;
			}, function() {
				scope.name = helloservice.name;
			});
		},
		templateUrl: '/assets/templates/bye.html'
	}
})
.factory('helloservice', function(){
	return new User();
});

function User() {
	this.name = '';

	this.setName = function( name ) {
		this.name = name;
	};

	this.getName = function() {
		return this.name;
	};
}