javascript - 为什么世博会的 MapView 无法正常工作

Question

我正在使用 expo 的 MapView 库！正如您在代码中看到的那样，一切都是逻辑，但它一直告诉我“道具coordinate.latitude在MapMarkerundefined

  "action": "press",
  "coordinate": Object {
    "latitude": 37.73174790670175,
    "longitude": -122.47094504535197,
  },
  "position": Object {
    "x": 352,
    "y": 307,
  },
}

这是我的代码：

const MapScreen = ({ navigation }) => {

  const MapRegion = {
    latitude: 37.78,
    longitude: -122.43,
    latitudeDelta: 0.0922,
    longitudeDelta: 0.0421,
  };
  const [newCoor, setNewCoor] = useState();

  let markerCoordinates;

  const selectLocationHandler = (event) => {
    console.log("ana", event.nativeEvent);
    setNewCoor({
      lat: event.nativeEvent.coordinate.latitude,
      lng: event.nativeEvent.coordinate.longitude,
    });
    console.log(newCoor);
  };
  if (newCoor) {
    markerCoordinates = {
      latitude: newCoor.latitude,
      longitude: newCoor.longitude,
    };
  }
  const savePickedLocationHandler = () => {
    if (!newCoor) {
      return;
    }
    navigation.navigate("NewPlaceScreen", { pickedLocation: newCoor });
  };

  useLayoutEffect(() => {
    navigation.setOptions({
      headerRight: () => (
        <TouchableOpacity
          style={{ marginHorizontal: 20 }}
          onPress={savePickedLocationHandler}
        >
          <Text
            style={{
              fontSize: 19,
              fontWeight: "bold",
              color: Platform.OS === "android" ? "#C06E00" : "white",
            }}
          >
            Save
          </Text>
        </TouchableOpacity>
      ),
    });
  }, []);
  
  return (
    <MapView
      style={styles.mapImage}
      region={MapRegion}
      onPress={selectLocationHandler}
    >
      {markerCoordinates && <Marker coordinate={markerCoordinates}></Marker>}
    </MapView>
  );
};

const styles = StyleSheet.create({
  mapImage: {
    flex: 1,
  },
});

export default MapScreen;