title: How to validate that at least one checkbox should be selected?
body: <p>I want to do validation for checkboxes here without form tag. <strong>At least one checkbox should be selected.</strong></p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;div *ngFor="let item of officeLIST"&gt;
    &lt;div *ngIf=" item.officeID == 1"&gt;
      &lt;input #off type="checkbox" id="off" name="off" value="1" [(ngModel)]="item.checked"&gt;
      &lt;label&gt;{{item.officename}}&lt;/label&gt;
    &lt;/div&gt;
  
    &lt;div *ngIf="item.officeID== 2"&gt;
      &lt;input #off type="checkbox" id="off" name="off" value="2" [(ngModel)]="item.checked"&gt;
      &lt;label&gt;{{item.officename}}&lt;/label&gt;
    &lt;/div&gt;
  
    &lt;div *ngIf="item.officeID== 3"&gt;
      &lt;input #off type="checkbox" id="off" name="off" value="3" [(ngModel)]="item.checked"&gt;
      &lt;label&gt;{{item.officename}}&lt;/label&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>for other field I will put required and do the error|touched|valid etc. but since checkbox is not single input, I cannot put required in every checkbox because all checkbox will be compulsory to checked. so how do I do the validation to alert user atleast one should be checked?</p>