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        <section class="multi-line-signature">
          <span class="returntype"><a href="dart-async/ControllerCallback.html">ControllerCallback</a></span>
          <span class="name ">onListen</span>
  
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        <section class="desc markdown">
  <p>The callback which is called when the stream is listened to.</p>
<p>May be set to <code>null</code>, in which case no callback will happen.</p>
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<section class="summary source-code" id="source"