title: How to disable or enable button according to if text boxes empty or not?
body: <p>I work on my angularjs projerct.</p>
  
  <p>I have  button in my template and two input text elements.</p>
  
  <p>The button have to be enabled only when two input boxes has some string.</p>
  
  <p>Here is HTML code:</p>
  
  <pre><code>    &lt;form id="loginform" class="form-horizontal" role="form"&gt;
          &lt;div style="margin-bottom: 25px" class="input-group"&gt;
              &lt;span class="input-group-addon"&gt;&lt;i class="glyphicon glyphicon-user"&gt;&lt;/i&gt;&lt;/span&gt;
              &lt;input id="login-username" type="text" class="form-control" ng-model="UserName" placeholder="UserName"&gt;
          &lt;/div&gt;
          &lt;div style="margin-bottom: 25px" class="input-group"&gt;
              &lt;span class="input-group-addon"&gt;&lt;i class="glyphicon glyphicon-lock"&gt;&lt;/i&gt;&lt;/span&gt;
              &lt;input id="login-password" type="text" class="form-control" ng-model="Password" placeholder="Password"&gt;
          &lt;/div&gt;
  
          &lt;div style="margin-top:10px" class="form-group pull-left"&gt;
              &lt;div class="col-sm-12 controls"&gt;
                  &lt;input type="button" 
                         class="btn btn-success" 
                         value="enter" 
                         ng-click="inspectorArea.verify(UserName,Password)" 
                         ng-disabled="(UserName == null || Password == null)"&gt;
              &lt;/div&gt;
          &lt;/div&gt;
      &lt;/form&gt;
  </code></pre>
  
  <p>and here is working <a href="http://plnkr.co/edit/5JnJkuLbde8w4E2IsLLp?p=preview" rel="nofollow noreferrer">plunker</a>.</p>
  
  <p>Using this row  <code>ng-disabled="(UserName == null || Password == null)</code> in input button element I disable or enable button.</p>
  
  <p>But it not working properly, you can see from plunker-example, button is enabled only when text boxes has string only for first time, if I remove string from one of the texts box elements the button is enable while I want them to be disalbled.</p>
  
  <p>Any idea how can I disable button if at least one of the text boxes is empty?</p>