title: why BackHandler.addEventListener triggers several times when click on back button of device?
body: <p>I created expo push notification.
  1) When I receive a notification I navigate to the screen of detailProduct using navigation.push and the same thing when I receive other notification.</p>
  
  <p>2) I made this statement</p>
  
  <pre><code>BackHandler.addEventListener ('hardwareBackPress', this.handleBackPress)
  </code></pre>
  
  <p>to listen to the event when I click on the back button.</p>
  
  <pre><code>handleBackPress = () =&gt; {
      console.log ("I clicked on the back button")
  }.
  </code></pre>
  
  <p>My question is, when I navigate to the product detail screen for example 2 times, and I click on the back button, it's perfectly normal I go back to the previous screen. But the <code>handleBackPress()</code> function will be executed 2 times i.e. the message will be displayed 2 times:</p>
  
  <pre><code>I clicked on the back button
  I clicked on the back button
  </code></pre>
  
  <p>Imagine when I navigate 5 or 6 times to the screen.
  the situation will be complicated. </p>
  
  <p>Why does <code>BackHandler.addEventListener</code> do that, and how do we run <code>BackHandler.addEventListener</code> once each time we click the back button?</p>