使用react-native-maps在Android上时，当使用newLatLngBounds(LatLngBounds, int)出现错误：“地图大小不能为零...”。

import React, { Component } from 'react';
import { View, Dimensions } from 'react-native';
import MapView from 'react-native-maps';


const {width, height} = Dimensions.get('window')

const SCREEN_HEIGHT = height
const SCREEN_WIDTH = width
const ASPECT_RATIO = width / height
const LATITUDE_DELTA = 0.0922
const LONGITUDE_DELTA = LATITUDE_DELTA * ASPECT_RATIO


class Map extends Component {
 
 constructor(props) {
  super(props)

  this.state = {
   isMapReady: false,
   initialPosition: {
    longitude: 0,
    latitude: 0,
    longitudeDelta: 0,
    latitudeDelta: 0
   },

   markerPosition: {
    longitude: 0,
    latitude: 0
   }

  }
 }

 watchID: ?number = null

 componentDidMount() {
  navigator.geolocation.getCurrentPosition((position) => {

   alert(JSON.stringify(position))

   var lat = parseFloat(position.coords.latitude)
   var long = parseFloat(position.coords.longitude)

   var initialRegion = {
    latitude: lat,
    longitude: long,
    latitudeDelta: LATITUDE_DELTA,
    longitudeDelta: LONGITUDE_DELTA
   }

   this.setState({initialPosition: initialRegion})
   this.setState({markerPosition: initialRegion})   
  },

  (error) => alert(JSON.stringify(error)))

  this.watchID = navigator.geolocation.watchPosition((position) => {
   var lat = parseFloat(position.coords.latitude)
   var long = parseFloat(position.coords.longitude)
   
   var lastRegion = {
    latitude: lat,
    longitude: long,
    longitudeDelta: LONGITUDE_DELTA,
    latitudeDelta: LATITUDE_DELTA
   }

   this.setState({initialPosition: lastRegion})
   this.setState({markerPosition: lastRegion})
  })

 }

 componentWillUnmount() {
  navigator.geolocation.clearWatch(this.watchID)
 }

 onMapLayout = () => {
    this.setState({ isMapReady: true });
  }

 render() {

  return (

   <View style={styles.containerStyle}>
    <MapView style={styles.mapStyle} initialRegion={this.state.initialPosition} onLayout={this.onMapLayout}>
     { this.state.isMapReady &&
      <MapView.Marker coordinate={this.state.markerPosition}>
      </MapView.Marker>
     }
    </MapView>
   </View>

   )

 }

}

const styles = {
 containerStyle: {
  flex:1,
  justifyContent: 'center',
  alignItems: 'center',
  backgroundColor: 'lightblue'
 },

 mapStyle: {
  left: 0,
  right: 0,
  top: 0,
  bottom: 0,
  position: 'absolute'
 }

}

export default Map;