Question

我在React中使用useState挂钩，当geojson触发onClick时，<source data={geojson}>的状态不会在_updateData中更新。我要更改onClick的更新后的geojson可以正确地在_updateData中使用console.log，但是data={geojson}不会更新和重新呈现。为了更新{geojson}的状态，我在这里缺少什么？谢谢你的帮助。正在使用的Mapbox库：https://uber.github.io/react-map-gl/#/

const Map = () => {
    const [viewport, setViewport] = useState({longitude: -98.58, latitude: 39.83, zoom: 3.5})
    const [geojson, setGeojson] = useState(null)

    useEffect(() => {
        // GeoJSON
        const locations = [];
        let ref = fire.database().ref("...").orderByKey();
        ref.once("value", snapshot => {
            snapshot.forEach(function(childSnapshot) {
                if (childSnapshot.val().Company !== "") {
                    locations.push(childSnapshot.val());
                }
                if (locations.length === 1219) {
                    var geojson = {
                        type: "FeatureCollection",
                        features: locations.map(item => {
                            return {
                                ...
                                },
                                geometry: {
                                type: "Point",
                                coordinates: [item.Long, item.Lat]
                                }
                            };
                        })
                    };
                    setGeojson(geojson);
                    return geojson;
                }
            });
        })
    });

    const _updateViewport = () => {
        setViewport(viewport)
    }

    const _updateData = () => {
        const locations = [];
        let ref = fire.database().ref("...").orderByKey();
        ref.once("value", snapshot => {
            snapshot.forEach(function(childSnapshot) {
                if (childSnapshot.val().Company !== "" && childSnapshot.val().Size === "Large") {
                    locations.push(childSnapshot.val());
                }
                if (locations.length === 232) {
                    var geojson = {
                        type: "FeatureCollection",
                        features: locations.map(item => {
                            return {
                                ...
                                },
                                geometry: {
                                type: "Point",
                                coordinates: [item.Long, item.Lat]
                                }
                            };
                        })
                    };
                    console.log(geojson);
                    setGeojson(geojson);
                    return geojson;
                }
            });
        })
    }

    return (
        <ReactMapGL
            {...viewport}
            onViewportChange={_updateViewport}
            width="100%"
            height="100%"
            mapStyle={mapStyle}
            mapboxApiAccessToken={TOKEN}>
            <Source type="geojson" data={geojson}>
                <Layer {...icon} />
            </Source>
            <div style={navStyle}>
                <NavigationControl onViewportChange={_updateViewport} />
                <button style={navStyle} onClick={_updateData}>Update</button>
            </div>
        </ReactMapGL>
    );
}

export default Map;

Answer 1

我建议您改用 useReducer 钩子，因为 useState 在让您知道更新时有点问题，我不知道为什么？！

Answer 2

如果只想首次加载，请使用如下所示的useEffect： useEffect(function,[dependency] or [])

反应useState钩子不更新状态onClick

2 个答案: