refactor(accordion): use optional binding for isOpen

Closes #1596

Author: bekos

src/accordion/accordion.js

@@ -54,46 +54,33 @@ angular.module('ui.bootstrap.accordion', ['ui.bootstrap.collapse'])
 })
 
 // The accordion-group directive indicates a block of html that will expand and collapse in an accordion
-.directive('accordionGroup', ['$parse', function($parse) {
+.directive('accordionGroup', function() {
   return {
     require:'^accordion',         // We need this directive to be inside an accordion
     restrict:'EA',
     transclude:true,              // It transcludes the contents of the directive into the template
     replace: true,                // The element containing the directive will be replaced with the template
     templateUrl:'template/accordion/accordion-group.html',
-    scope:{ heading:'@' },        // Create an isolated scope and interpolate the heading attribute onto this scope
+    scope: { 
+      heading: '@',               // Interpolate the heading attribute onto this scope
+      isOpen: '=?'
+    },
     controller: function() {
       this.setHeading = function(element) {
         this.heading = element;
       };
     },
     link: function(scope, element, attrs, accordionCtrl) {
-      var getIsOpen, setIsOpen;
-
       accordionCtrl.addGroup(scope);
 
-      scope.isOpen = false;
-      
-      if ( attrs.isOpen ) {
-        getIsOpen = $parse(attrs.isOpen);
-        setIsOpen = getIsOpen.assign;
-
-        scope.$parent.$watch(getIsOpen, function(value) {
-          scope.isOpen = !!value;
-        });
-      }
-
       scope.$watch('isOpen', function(value) {
         if ( value ) {
           accordionCtrl.closeOthers(scope);
         }
-        if ( setIsOpen ) {
-          setIsOpen(scope.$parent, value);
-        }
       });
     }
   };
-}])
+})
 
 // Use accordion-heading below an accordion-group to provide a heading containing HTML
 // <accordion-group>

src/accordion/docs/demo.html

@@ -4,8 +4,8 @@
     Open only one at a time
   </label>
 
-  <accordion close-others="oneAtATime">
-    <accordion-group heading="Static Header, initially expanded" is-open="true">
+  <accordion close-others="oneAtATime" ng-init="isFirstOpen = true">
+    <accordion-group heading="Static Header, initially expanded" is-open="isFirstOpen">
       This content is straight in the template.
     </accordion-group>
     <accordion-group heading="{{group.title}}" ng-repeat="group in groups">