Angular ngController vs Controller constructed within Directive

Question

I'm wondering what the use cases are for these two methods of creating a controller:

Using ngController:

myApp.controller('myController', ['$scope', function ( $scope ) {

}]);

Constructing the controller within a directive with the controller attribute:

myApp.directive ( 'myDirective', [ '$window', function( $window ) {
    return {
        restrict: 'A',
        controller: [ '$scope', function( $scope ) {

        }],
        link: function( scope, element, attrs ) {

        }
    };
}]);

Is there any reason you wouldn't construct the controller within a directive if they were both invoked on the same element?

Is it simply a question of how widely used / complex the controller is?

Answer 1

The reason to use directive controller is condensed in one sentence:

To create reusable components

Directive controller should contain logic of the component that could be reused. Using directive controller together with isolate scope is the way to create reusable components.

Take a paginator as an example: a paginator needs some logic to notify other component (a grid for example) of the current selected page changed so that the grid can update accordingly. These logic could be written inside directive controller to be reused. When using together with isolate scope, this scope is not tight to application controller'scope and it's easy for you to configure pageSize to bind to any property of the application controller's scope.

Answer 2

There is a subtle difference between a normal controller ( one created using ng-controller or routes ) and a directive controller.

1. A Directive controller is allowed to inject $element. Note that while currently you can inject $element into a normal controller as well, its bad practice to do so.

2. The sole purpose of a directive controller is for directive to directive communication. A very good use case is show on the main page of AngularJS for tabs component.

A directive controller allows directives to have functions. Because these controller instances can be 'required' in other directives - other directives can communicate / operate on this directive using the controller instance.

The only reason to use a controller with a directive is if you want to do some kind of directive to directive communication. For anything else you should probably stick with writing all your scope logic in the linking function.