Using ng-class in Angular.js with a boolean retrieved from a service: A step-by-step guide

I need to dynamically set a class based on a boolean value that is determined in a service. This example is simplified for readability, but in reality, the boolean would be set by multiple functions within the service.

Here is how it would look in HTML:

<div ng-controller="MainController">
    <div ng-class="{ 'green' : MainController.CustomService.isGreen }">
    </div>
</div>

The service code would be like this:

App.service("CustomService", function() {
    this.isGreen = true;
})

And the controller code would look something like this:

App.controller('MainController', ['$scope', 'CustomService',  function($scope, CustomService) {

}]);

Answer №1

Here is an alternative approach:

App.controller('MainController', ['$scope', 'CustomService',  function($scope, CustomService) {
    $scope.isGreen = CustomService.isGreen;
}]);

For the HTML:

<div ng-class="{ 'green' : isGreen }">

The view does not have direct access to the service. It has access to the $scope object. Therefore, if you need something in the view, you must define it in the $scope first.

If you want to track the color:

App.controller('MainController', ['$scope', 'CustomService',  function($scope, CustomService) {
    $scope.isGreen = function () {
        return CustomService.isGreen;
    };
}]);

And for the HTML:

<div ng-class="{ 'green' : isGreen() }">

Answer №2

Accessing properties of $scope is limited to the view. So, when referencing

MainController.CustomService.isGreen
in the view, Angular tries to access
$scope.MainController.CustomService.isGreen
, which does not exist. To resolve this, you need to expose the service to the scope in your controller.

App.controller('MainController', ['$scope', 'CustomService',  function($scope, CustomService) {
    $scope.CustomService = CustomService;
}]);

Once done, you can use your service in the view like this:

<div ng-class="{ 'green' : CustomService.isGreen }">
</div>

Another common approach is to direct the controller to expose itself in the scope. This can be achieved by adjusting the ng-controller attribute value to MainController as $ctrl (the name can vary but $ctrl is standard in Angular 1.5). Subsequently, $ctrl becomes accessible in your view:

<div ng-class="{ 'green' : $ctrl.CustomService.isGreen }">
</div>

In this scenario within the controller function, $ctrl represents this. Thus, to publish the service, you would write:

App.controller('MainController', ['CustomService',  function(CustomService) {
        this.CustomService = CustomService;
}]);

You will observe that there is no need to include $scope as a parameter anymore.

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