Fortunately, I was able to provide a solution in a comment on the question, but I feel it's important to share a comprehensive answer here to mark this question as "Answered".
The approach you take when sharing a controller depends on your specific goals; you can either have different instances of the same controller be shared between components, or you can share the exact same instance of the controller.
Sharing a Controller Instance
To have two directives utilize the same controller instance, you can achieve this by passing the same method to both directives, as illustrated below:
app.controller( 'MyCtrl', function ( $scope ) {
// perform actions...
});
app.directive( 'directiveOne', function () {
return {
controller: 'MyCtrl'
};
});
app.directive( 'directiveTwo', function () {
return {
controller: 'MyCtrl'
};
});
Each directive will possess its own instance of the controller, enabling you to share the underlying logic across multiple components.
Requiring a Controller
If your intention is to share the same instance of a controller, utilizing require is the way to go.
By using require, you ensure that another directive is present and then integrate its controller as a parameter within the link function. For scenarios where there are two directives on one element, your directive can require the presence of the other directive and thereby access its controller methods. A common scenario for this is requiring ngModel.
^require, indicated by adding the caret symbol, checks elements above the current directive along with the current element to locate the specified directive. This capability facilitates the creation of intricate components where "sub-components" can communicate with the parent component via its controller for enhanced functionality. Examples could include tabbed interfaces, where individual panes can interact with the overarching tabs for seamless switching; or an accordion set that ensures only one panel is open at any given time; and so forth.
In all cases, you must use both directives simultaneously for this mechanism to be effective. require serves as a communication bridge between components.
For further details, refer to the Directives Guide page: http://docs.angularjs.org/guide/directive