feat(events): add open-close callback

Adds a new `uisOpenClose` directive which allows a callback to be 
defined that is called whenever the dropdown is opened or closed.

Callback is passed an isOpen parameter which is set to true if the
dropdown has been opened, otherwise false.

Closes #432, closes #1153

src/uisOpenCloseDirective.js

@@ -0,0 +1,19 @@
+uis.directive('uisOpenClose', ['$parse', '$timeout', function ($parse, $timeout) {
+  return {
+    restrict: 'A',
+    require: 'uiSelect',
+    link: function (scope, element, attrs, $select) {
+      $select.onOpenCloseCallback = $parse(attrs.uisOpenClose);
+
+      scope.$watch('$select.open', function (isOpen, previousState) {
+        if (isOpen !== previousState) {
+          $timeout(function () {
+            $select.onOpenCloseCallback(scope, {
+              isOpen: isOpen
+            });
+          });
+        }
+      });
+    }
+  };
+}]);

test/select.spec.js

@@ -1375,6 +1375,32 @@ describe('ui-select tests', function() {
     expect(scope.$model).toBe(scope.$item);
   });
 
+  it('should call open-close callback with isOpen state as first argument on open and on close', function () {
+
+    var el = compileTemplate(
+      '<ui-select uis-open-close="onOpenCloseFn(isOpen)" ng-model="selection.selected"> \
+        <ui-select-match placeholder="Pick one...">{{$select.selected.name}}</ui-select-match> \
+        <ui-select-choices repeat="person.name as person in people | filter: $select.search"> \
+          <div ng-bind-html="person.name | highlight: $select.search"></div> \
+          <div ng-bind-html="person.email | highlight: $select.search"></div> \
+        </ui-select-choices> \
+      </ui-select>'
+    );
+
+    scope.onOpenCloseFn = function(){};
+    spyOn(scope, 'onOpenCloseFn');
+
+    openDropdown(el);
+    $timeout.flush();
+    expect(scope.onOpenCloseFn).toHaveBeenCalledWith(true);
+
+    closeDropdown(el);
+    $timeout.flush();
+    expect(scope.onOpenCloseFn).toHaveBeenCalledWith(false);
+
+    expect(scope.onOpenCloseFn.calls.count()).toBe(2);
+  });
+
   it('should allow creating tag in single select mode with tagging enabled', function() {
 
     scope.taggingFunc = function (name) {