Reuse ngClass directive in AngularJS -

i trying validate form , there way logic in html page. using ngmessages because it's quite hopeless without it.

i doing object variant of ng-class this

ng-class="{ 'has-error' : registerform.username.$invalid && registerform.username.$touched, 'has-success' : registerform.username.$valid && registerform.username.$touched }" 

as can see there alot of code in above line. have use directive 6 times option seems right copy paste 5 other places. tried doing did not work

<form ng-init="formgroupclassobject = { 'has-error' : registerform.username.$invalid && registerform.username.$touched, 'has-success' : registerform.username.$valid && registerform.username.$touched }">  <div class="form-group" ng-class="formgroupclassobject"></div> 

i don't understand why not work. have other suggestions on reuse-ability of code above?

how about:

ng-class="getformclasses(registerform)" 

and in common controller:

$scope.getformclasses = function(form) {   if (!form) { return; }   return {     'has-error'  : form.username.$invalid && form.username.$touched,     'has-success': form.username.$valid   && form.username.$touched   } }; 

if use ng-init, classes not updated when form validity changes.