Identify graphics

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// Copyright 2024 Esri
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

import 'package:arcgis_maps/arcgis_maps.dart';
import 'package:flutter/material.dart';

class IdentifyGraphics extends StatefulWidget {
  const IdentifyGraphics({super.key});

  @override
  State<IdentifyGraphics> createState() => _IdentifyGraphicsState();
}

class _IdentifyGraphicsState extends State<IdentifyGraphics> {
  // Create a controller for the map view.
  final _mapViewController = ArcGISMapView.createController();
  // Graphic to store the polygon.
  late final Graphic _graphic;
  // Graphics overlay to present the graphics for the sample.
  final _graphicsOverlay = GraphicsOverlay();
  // A flag for when the map view is ready and controls can be used.
  var _ready = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: [
          Column(
            children: [
              Expanded(
                // Add a map view to the widget tree and set a controller.
                child: ArcGISMapView(
                  controllerProvider: () => _mapViewController,
                  onMapViewReady: onMapViewReady,
                  onTap: onTap,
                ),
              ),
            ],
          ),
          // Display a progress indicator and prevent interaction until state is ready.
          Visibility(
            visible: !_ready,
            child: const SizedBox.expand(
              child: ColoredBox(
                color: Colors.white30,
                child: Center(child: CircularProgressIndicator()),
              ),
            ),
          ),
        ],
      ),
    );
  }

  void onMapViewReady() async {
    // Create a map with a topographic basemap.
    final map = ArcGISMap.withBasemapStyle(BasemapStyle.arcGISTopographic);
    // Create a polygon geometry.
    final polygonBuilder = PolygonBuilder(
      spatialReference: _mapViewController.spatialReference,
    );
    // Add points to the polygon.
    polygonBuilder.addPointXY(x: -20e5, y: 20e5);
    polygonBuilder.addPointXY(x: 20e5, y: 20e5);
    polygonBuilder.addPointXY(x: 20e5, y: -20e5);
    polygonBuilder.addPointXY(x: -20e5, y: -20e5);
    // Create a graphic with the polygon geometry and a yellow fill symbol.
    _graphic = Graphic(
      geometry: polygonBuilder.toGeometry(),
      symbol: SimpleFillSymbol(
        style: SimpleFillSymbolStyle.solid,
        color: Colors.yellow,
      ),
    );

    // Add the graphics to the graphics overlay.
    _graphicsOverlay.graphics.add(_graphic);
    // Add the graphics overlay to the map view controller.
    _mapViewController.graphicsOverlays.add(_graphicsOverlay);
    // Set the viewpoint to the graphic.
    _mapViewController.setViewpoint(
      Viewpoint.fromTargetExtent(_graphic.geometry!.extent),
    );
    // Set the map to the map view controller.
    _mapViewController.arcGISMap = map;
    // Set the ready state variable to true to enable the sample UI.
    setState(() => _ready = true);
  }

  void onTap(Offset offset) async {
    // Identify the graphics overlay at the tapped point.
    final identifyGraphicsOverlay =
        await _mapViewController.identifyGraphicsOverlay(
      _graphicsOverlay,
      screenPoint: offset,
      tolerance: 12.0,
      maximumResults: 10,
    );
    // Check if the identified graphic is the same as the sample graphic.
    if (identifyGraphicsOverlay.graphics.isNotEmpty) {
      final identifiedGraphic = identifyGraphicsOverlay.graphics.first;
      if (identifiedGraphic == _graphic) {
        if (mounted) {
          showDialog(
            context: context,
            builder: (context) {
              // Display an alert dialog when the graphic is tapped.
              return AlertDialog(
                alignment: Alignment.center,
                content: const Text('Tapped on Graphic'),
                actions: [
                  TextButton(
                    onPressed: () => Navigator.of(context).pop(),
                    child: const Text('OK'),
                  ),
                ],
              );
            },
          );
        }
      }
    }
  }
}