Digikam-FatClient/src/map.js

import React, { useEffect, useState } from 'react';

import { makeStyles } from '@material-ui/core/styles';
import Box from '@material-ui/core/Box';

import "leaflet/dist/leaflet.css"

import L from 'leaflet';

export function MapView(props) {
    // This is bad React design: this component holds state which the parent needs (the Leaflet map object).
    // Normally we'd make such an object in the parent and pass it as a prop. However, the object cannot
    // be created without a div being present for it to reside in, so we have a chicken-egg problem.
    // We solve it by loading the map after mounting this component, then passing a handle to the parent.
    const { onMapChange, style } = props;
    const [map, setMap] = useState(null);
    const [camera, setCameraNoPush] = useState([51.505, -0.09, 13]); //lat, long, zoom

    var _ = require('lodash');
    const id = _.uniqueId("leaflet_map_");

    function updateCamera() {
        var c = map.getCenter();
        var z = map.getZoom();
        setCameraNoPush([c[0], c[1], z]);
    }

    // Initialize the map on mount.
    useEffect(() => {
        setMap(L.map(id, {
            center: [camera[0], camera[1]],
            zoom: camera[2],
            layers: [
                L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png', {
                    attribution: '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
                }),
            ]
        }
        ));
    }, [])

    // Notify parent if map object changes.
    useEffect(() => {
        if (onMapChange) {
            onMapChange(map);
        }
    }, map);

    // Update camera state of this component when map changes.
    useEffect(() => {
        if (map != null) {
            map.on('move', function (e) {
                updateCamera();
            });
            map.on('zoom', function (e) {
                updateCamera();
            });
        }
    }, [map])

    return <div id={id} style={style}></div>
}