set zoom from atitudeDelta

Author: kasajei

docs/stories/index.js

@@ -27,7 +27,12 @@ storiesOf('MapView', module)
   .add('options', () => (
     <View style={styles.container}>
       <MapView
-        initialRegion={{ latitude: 48.86, longitude: 2.34 }}
+        initialRegion={{
+          latitude: 48.86,
+          longitude: 2.34,
+          latitudeDelta: 0.1,
+          longitudeDelta: 0.1,
+        }}
         options={{
           zoomControlOptions: {
             position: window.google.maps.ControlPosition.RIGHT_CENTER,

src/index.js

@@ -54,7 +54,12 @@ class MapView extends Component {
             lng: initialRegion.longitude,
           },
         };
-
+    const zoom =
+      region && region.latitudeDelta
+        ? Math.round(Math.log(360 / region.latitudeDelta) / Math.LN2)
+        : initialRegion && initialRegion.latitudeDelta
+        ? Math.round(Math.log(360 / initialRegion.latitudeDelta) / Math.LN2)
+        : 15;
     return (
       <View style={style}>
         <GoogleMapContainer
@@ -64,7 +69,7 @@ class MapView extends Component {
           {...centerProps}
           onDragStart={onRegionChange}
           onIdle={this.onDragEnd}
-          defaultZoom={15}
+          defaultZoom={zoom}
           onClick={onPress}
           options={options}>
           {this.props.children}