title: ReactNative componentDidMount doesn't get called
body: <p>I have two screens: A and B, connected with a StackNavigator</p>
  
  <p>Screen A is a QR code scanner. As soon as a QR code is scanned, it navigates to screen B.</p>
  
  <p>In screen B, I make an API call using the QR code that gets passed as a navigation param from screen A. I trigger this API call in componentDidMount.</p>
  
  <p>My issue is: if I navigate from A to B, then back to A, then to B again, componentDidMount does not get called and I have no way to trigger the API call.</p>
  
  <hr>
  
  <h1>EDIT:</h1>
  
  <p>Here's some code</p>
  
  <p><strong>Screen A</strong> </p>
  
  <p>Handler function that gets called when a QR code is scanned:</p>
  
  <pre><code>handleQRCode = qrCode =&gt; {
      NavigationService.navigate('Decode', {qrCode});
  };
  </code></pre>
  
  <p><strong>Screen B</strong> </p>
  
  <p>The QR code is pulled from the navigation state params and used for an API call (startDecode) through redux.</p>
  
  <pre><code>componentDidMount() {
      qrCode = this.props.navigation.state.params.qrCode;
      this.props.startDecode(qrCode.data);
  }
  </code></pre>
  
  <p>My issue is that componentDidMount only gets called the first time that route is taken.</p>