Question 250441 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – React-Leaflet always redraws the map with "MouseMove"

I want to display the geo coordinates when the mouse moves in my React app. I noticed that with "Mousemove" the map is repeatedly redrawn with all objects with a large number. How can I prevent this and only update the coordinates?

Here is the Code:

export class MapView extends Component {

state = {
lat: 10,
lon: 50,
tileName: "",
tiles: [],
};

MouseMove = () => {
const map = useMapEvent("mousemove", (e) => {
  let lon = e.latlng.lng;
  let lat = e.latlng.lat;

  this.setState({
    lat: lat.toFixed(6),
    lon: lon.toFixed(6),
    tileName: this.getTileNameSRTM(lon, lat),
  });
});
};

render() {
let self = this;
const matrix = this.props.matrix;

function renderMatrix() {
  if (matrix !== null) {
    return (
      <div>
        <Rectangle bounds={matrix.rect} pathOptions={{ color: "Blue" }} />
      </div>
    );
  }
}

function Zoom() {
  const map = useMapEvent("zoom", (e) => {
    console.log("zoom");
    self.drawTile(map, self);
  });
  return self.state.tiles;
}

function Pan() {
  const map = useMapEvent("move", (e) => {
    console.log("pan");
    //self.drawTile(map, self);
  });
  return self.state.tiles;
}

return (
  <div
    className="w3-col w3-margin-left w3-margin-right"
    style={{ width: "calc(80% - 2*16px)" }}
  >
    <div className="w3-container w3-blue w3-margin-top w3-margin-bottom w3-padding">
      <FontAwesomeIcon icon="fa-solid fa-map" className="w3-margin-right" />
      Map Viewer Latitude: {this.state.lat} Longitude: {this.state.lon}{" "}
      <label className="w3-right">{this.state.tileName}</label>
    </div>
    <MapContainer
      center={[50.65935313570456, 10.665137544640139]}
      zoom={5}
      style={{ height: "calc(100vh - 157.48px - 31px - 5*16px)" }}
      scrollWheelZoom={true}
    >
      <TileLayer
        attribution='&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
        url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
      />
      <this.MouseMove />
      <Zoom />
      <Pan />
    </MapContainer>
  </div>
 );
 }
}

export default MapView;

The source code is incomplete, I have only posted the affected parts.

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    This is the working code (as always read the manual first "https://react-leaflet.js.org/docs/example-external-state/"):

    function DisplayPosition({ map }) {
  const [position, setPosition] = useState(() => map.getCenter());

  const onMove = useCallback((e) => {
    setPosition(e.latlng);
  }, []);

  useEffect(() => {
    map.on("mousemove", onMove);
    return () => {
      map.off("mousemove", onMove);
    };
  }, [map, onMove]);

  return (
    <div className="w3-container w3-blue w3-margin-top w3-margin-bottom w3-padding">
      <FontAwesomeIcon icon="fa-solid fa-map" className="w3-margin-right" />
      Map Viewer Latitude: {position.lat.toFixed(6)} Longitude:{" "}
      {position.lng.toFixed(6)}{" "}
      <label className="w3-right">
        {self.getTileNameSRTM(position.lat, position.lng)}
      </label>
    </div>
  );
}

function FinalMap() {
  const [map, setMap] = useState();

  const displayMap = useMemo(
    () => (
      <MapContainer
        center={[50.65935313570456, 10.665137544640139]}
        zoom={5}
        style={{ height: "calc(100vh - 157.48px - 31px - 5*16px)" }}
        scrollWheelZoom={true}
        ref={setMap}
      >
        <TileLayer
          attribution='&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
          url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
        />
        <DrawTiles />
        <Greeting></Greeting>
      </MapContainer>
    ),
    []
  );

  return (
    <div>
      {map ? <DisplayPosition map={map} /> : null}
      {displayMap}
    </div>
  );
}

  2. 0

    Use react memo to skip re-rending in react
    https://react.dev/reference/react/memo
    Wrap your map component with memo

    export default memo(MapView)
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