angularjs - Adding form validation to custom directive in angular -

i aware question has been asked before not know how implement asnwers problem. have tri-state boolean directive in angular , not sure how add validation states directive form can see value valid (not null)

app.directive('customboolean', function(){     return {     restrict: 'e',     replace: true,     scope: {         boolvalue: '=',         required: '@'     },     template: '<button class="btn btn-default btn-xs" ng-click="toggle()" style="width: 70px">{{ boolvalue | bool_to_string }}</button>',     controller: function ($scope, $element){      $scope.toggle = function(){         if ($scope.boolvalue == null)         { $scope.boolvalue = true; }         else if ($scope.boolvalue == true)         { $scope.boolvalue = false; }         else { $scope.boolvalue = $scope.required ? true  : undefined; }     };   }  } }); 

below plnkr link of have far. have ideas?

plnkr link

use ngmodel instead of boolvalue. require ngmodel in directive, , set validity using $setvalidity.

app.directive('customboolean', function(){ return { restrict: 'e', require : 'ngmodel' replace: true, scope: {     boolvalue: '=',     required: '@' }, template: '<button class="btn btn-default btn-xs" ng-click="toggle()" style="width: 70px">{{ boolvalue | bool_to_string }}</button>', link: function ($scope, $element,$attrs,ngmodel){ if (//your invalid conditions){   ngmodel.$setvalidity(attrs.ngmodel,true/false); } $scope.toggle = function(){     if ($scope.boolvalue == null)     { $scope.boolvalue = true; }     else if ($scope.boolvalue == true)     { $scope.boolvalue = false; }     else { $scope.boolvalue = $scope.required ? true  : undefined; } }; }}});