title: How to make selecting a radio button required before submitting
body: <p>I have a series of questions which have radio answer choices.  I can't figure out how to use AngularJS validation to require the user to select one before clicking "Next".  Below is my code:</p>
  
  <p>EDIT:  Please note that clicking "Next" gets the next question node from the controller depending on what choice was made.  It's basically a dynamic questionnaire.</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;form novalidate&gt;
     &lt;div class="radio" ng-repeat="answer in node.Answers"&gt;
        &lt;input type="radio" name="answerGroup" ng-model="$parent.selectedAnswer" 
           value="{{answer.BranchId}},{{node.LeafId}},{{answer.Id}}"/&gt; {{answer.Text}} 
     &lt;/div&gt;
     &lt;div&gt;
        &lt;input type="button" ng-click="previous()" value="Previous"/&gt;
        &lt;input type="button" ng-click="next(selectedAnswer)" value="Next"/&gt;
     &lt;/div&gt;
  &lt;/form&gt;
  </code></pre>