       <span class="returntype"><a href="dart-async/ControllerCancelCallback.html">ControllerCancelCallback</a></span>
                  <span class="name ">onCancel</span>
          
</section>
        
                <section class="desc markdown">
          <p>The callback which is called when the stream is canceled.</p>
<p>May be set to <code>null</code>, in which case no callback will happen.</p>
        </section>
                <section class="summary source-code" id="source">
          <h2><span>I