title: UIApplication.didBecomeActiveNotification Gets Called One-time Unexpectedly When User Swipe Down the Notification Center Screen on iOS Device
body: <p>like the title says, I found this <em>unexpected</em> behavior in iOS 11 &amp; 12.<br>
  Does anyone know why this event gets called and, <strong>more importantly</strong>, is there any workaround to prevent system from firing this <code>UIApplication.didBecomeActiveNotification</code> event out?</p>
  
  <p>Here are the steps to reproduce this behavior:</p>
  
  <ol>
  <li>Run the application.</li>
  <li>Access the Notification Center Screen on iPhone or iPad(by swiping downward from the very top of the device's screen).</li>
  <li>At the time when the Notification Center Screen <strong>gets to the bottom of the device's screen</strong>, a <code>UIApplication.didBecomeActiveNotification</code> event gets fired.</li>
  </ol>
  
  <p>You can simply add a log in AppDelegate.swift file for testing, like:</p>
  
  <pre class="lang-swift prettyprint-override"><code>func applicationDidBecomeActive(_ application: UIApplication) {
          print("applicationDidBecomeActive")
  }
  </code></pre>
  
  <p>I call it <em>unexpected</em> because when the Notification Center Screen appears, the application literally should turn to (at least semi-)background-mode and not turn back to foreground-mode unless the Notification Center Screen disappears(e.g. by swiping up to the upper-most top of the screen).<br>
  I also observed that the event did not get fired when the Control Center Screen shows up.</p>
  
  <p>In my app, I'm trying the control the status of a video player when the app goes to the background(or semi-background). The unexpected <code>.didBecomeActiveNotification</code> event annoys the status-controlling workflow.</p>
  
  <p>I searched on the <a href="https://openradar.appspot.com/page/1" rel="noreferrer">Open Radar</a> and here and googled for a while and no such related topic appeared.</p>
  
  <p>Any suggestion would be appreciated. Thank you.</p>