ss.html">platformBrightness</a> changes value.</p>
<p>The framework invokes this callback in the same zone in which the
callback was set.</p>
<p>See also:</p>
<ul>
<li><code>WidgetsBindingObserver</code>, for a mechanism at the widgets layer to
observe when this callback is invoked.</li>
</ul>
        </section>
                <section class="summary source-code" id="source">
          <h2><span>Implementation</span></h2>
          <pre class="language-dart"><code class="language-dart">VoidCallback get onP