title: React-native : how to get coordinates and delta of visible area in MapView component
body: <p>Say I have a map defined in react native this way :</p>
  
  <pre><code>    render() {
          return (
              &lt;View style={{flex: 1, position: 'relative'}}&gt;
                  &lt;MapView
                      style={styles.map}
                      showsUserLocation={this.state.showsUserLocation}
                      region={{
                          latitude: 48.8534100,
                          longitude: 2.3378000,
                          latitudeDelta: 0.12,
                          longitudeDelta: 0.065
                      }}
                      onRegionChangeComplete={
                          () =&gt; {
                              // How to retrieve coordinates and Delta when user moves the map
                              console.log(this.region);
                          }
                      } /&gt;
              &lt;/View&gt;
          );
      }
  </code></pre>
  
  <p>How to retrieve the coordinates and Delta when the user moves on the map ?</p>