Q:

Using the AngularJS require option to call into another directive

I was just reading here about accessing one directive's controller from within another directive via the require option:
  http://jasonmore.net/angular-js-directives-difference-controller-link/

The directive droppable and dashboard declarations in on my view - on two different divs:
  <div class="wrapper wrapper-content animated fadeInRight">
<div class="row">        
    <div class="col-lg-12" data-droppable drop="handleDrop">
        <div id="dash" dashboard="dashboardOptions" class="dashboard-container"></div>
    </div>
</div>

However I can't seem to get it to work. My dashboardCtrl param below is NULL.
Here in my droppable directive, I use the REQUIRE option:
  .directive('droppable', function () {
return {
    scope: {
        drop: '&',
    },
    //****************** dashboard directive is optionally requested ************
    require: '?dashboard', 

    link: function (scope, element, attributes, dashboardCtrl) {
         el.addEventListener('drop', function (e) {

            if (e.preventDefault) { e.preventDefault(); }

            this.classList.remove('over');
            var item = document.getElementById(e.dataTransfer.getData('Text'));                
            this.appendChild(item.cloneNode(true));

            // *** CALL INTO THE dashboardCtrl controller ***
            dashboardCtrl.addWidgetInternal();

            return false;
        }, false);
    }
}
});

and the dashboard directive :
 angular.module('ui.dashboard')
.directive('dashboard', ['WidgetModel', 'WidgetDefCollection', '$modal', 'DashboardState', '$log', function (WidgetModel, WidgetDefCollection, $modal, DashboardState, $log) {
  return {
      restrict: 'A',
      templateUrl: function (element, attr) {
          return attr.templateUrl ? attr.templateUrl : 'app/shared/template/dashboard.html';
      },
      scope: true,      
      controller: ['$scope', '$attrs', function (scope, attrs) {
            // ommitted for brevity
        }],
      link: function (scope) {                
            scope.addWidgetInternal = function (event, widgetDef) {
              event.preventDefault();
              scope.addWidget(widgetDef);
          };
      };
   }
}]);

However, my dashboardCtrl parameter is NULL. Please help me to figure out how to use require.
I actually need to call the addWidget() function, which is within the link option; but I suppose I can copy or move that into the controller option.
thank you !
Bob

A:

Here is an example of "parent" directive dashboard requiring droppable, and communication between the two making use of require and passing dashboardCtrl
Here is a good article to see directive to directive communication
Fiddle example also built from your previous question
JSFiddle
app.directive('droppable', [function () {
    return {
        restrict: 'A',
        require: 'dashboard',
        link: function (scope, elem, attrs, dashboardCtrl) {

            dashboardCtrl.controllerSpecificFunction('hello from child directive!');

            scope.addWidgetInternal = function(message) {
                console.log(message);
            }
        }
    }
}]);

app.directive('dashboard', [function () {
    return {
        restrict: 'A',
        controller: function ($scope) {
            $scope.handleDrop = function(message) {
                $scope.addWidgetInternal(message)
            }

            this.controllerSpecificFunction = function(message) {
                console.log(message);
           }
        }
    }
}]);

Edit
Based on discussion, here is a solution for what I currently understand the problem to be
Parent directive dashboard optionally requires child directive droppable and there needs to be communication between the two
<div dashboard>
    <button id="dash" droppable ng-click="handleDrop($event)">Handle Drop</button>
</div>

app.directive('droppable', [function () {
    return {
        restrict: 'A',
        require: '^?dashboard',
        link: function (scope, elem, attrs, dashboardCtrl) {
            scope.handleDrop = function($event) {
                dashboardCtrl.addWidgetInternal($event);
            }
        }
    }
}]);

app.directive('dashboard', [function () {
    return {
        restrict: 'A',
        controller: function ($scope) {
            this.addWidgetInternal = function($event) {
                console.log($event);
           }
        }
    }
}]);

Updated JSFiddle

