Contingent values

Valid coded values for a field constrained by another (bird-nests geodatabase).

iOS

This is the real source of the example app’s contingent-values screen — run it on a device or simulator to see it live.

app/editing/contingent-values.tsx

import {
  FeatureLayer,
  Map,
  MapView,
  offline,
  type FeatureLayerHandle,
  type GeodatabaseHandle,
} from 'expo-arcgis';
import { Asset } from 'expo-asset';
import { useEffect, useRef, useState } from 'react';
import { Button } from '../../components/ui/button';

import { SampleScreen } from '../../src/SampleScreen';

// The Esri "Contingent Values Bird Nests" mobile geodatabase. Its `BirdNests` table defines a
// contingent-values constraint: a nest's valid `Protection` depends on its `Status`.
const GDB = require('../../assets/birdnests.geodatabase');

/**
 * Contingent values express that one field's allowed values depend on another's. Here a bird nest's
 * valid `Protection` codes are contingent on its `Status` — `contingentValues({Status}, 'Protection')`
 * returns only the codes permitted for that status.
 */
export default function ContingentValues() {
  const gdb = useRef<GeodatabaseHandle | null>(null);
  const [layer, setLayer] = useState<FeatureLayerHandle | null>(null);
  const [status, setStatus] = useState('Loading bird-nests geodatabase…');

  const showFor = async (handle: FeatureLayerHandle, nestStatus: string) => {
    const options = await handle.contingentValues({ Status: nestStatus }, 'Protection');
    setStatus(`Protection valid for ${nestStatus}: ${options.map((o) => o.name).join(', ') || '—'}`);
  };

  useEffect(() => {
    (async () => {
      const asset = await Asset.fromModule(GDB).downloadAsync();
      const path = (asset.localUri ?? asset.uri).replace('file://', '');
      gdb.current = await offline.openGeodatabase(path);
      const fl = gdb.current.getFeatureLayer('BirdNests');
      setLayer(fl);
      await showFor(fl, 'OCCUPIED');
    })().catch((e) => setStatus(String(e)));
  }, []);

  const tap = (nestStatus: string) => () => {
    if (layer) showFor(layer, nestStatus).catch((e) => setStatus(String(e)));
  };

  return (
    <SampleScreen
      status={status}
      controls={
        <>
          <Button title="Occupied" onPress={tap('OCCUPIED')} />
          <Button title="Unoccupied" onPress={tap('UNOCCUPIED')} />
        </>
      }
    >
      <Map basemap="arcGISTopographic" initialViewpoint={{ latitude: 34.4, longitude: -118.92, scale: 200_000 }}>
        {layer && <FeatureLayer layer={layer} />}
        <MapView style={{ flex: 1 }} />
      </Map>
    </SampleScreen>
  );
}