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ArcGIS Runtime SDK for .NET

Feature layer query

This code sample is available for these platforms:
View Sample on GitHub

Find features in a feature table which match an SQL query.

Image of feature layer query

Use case

Query expressions can be used in ArcGIS to select a subset of features from a feature table. This is most useful in large or complicated data sets. A possible use case might be on a feature table marking the location of street furniture through a city. A user may wish to query by a TYPE column to return "benches". In this sample, we query a U.S. state by STATE_NAME from a feature table containing all U.S. states.

How to use the sample

Input the name of a U.S. state into the text field. When you tap the button, a query is performed and the matching features are highlighted or an error is returned.

How it works

  1. Create a ServiceFeatureTable using the URL of a feature service.
  2. Create a QueryParameters with a where clause specified using the WhereClause property.
  3. Perform the query using QueryFeaturesAsync(query) on the service feature table.
  4. When complete, the query will return a FeatureQueryResult which can be iterated over to get the matching features.

Relevant API

  • FeatureLayer
  • FeatureQueryResult
  • QueryParameters
  • ServiceFeatureTable

About the data

This sample uses U.S. State polygon features from the USA 2016 Daytime Population feature service.

Tags

search, query

Sample Code

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"             
             xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms"
             xmlns:mapping="clr-namespace:Esri.ArcGISRuntime.Mapping;assembly=Esri.ArcGISRuntime" 
             x:Class="ArcGISRuntime.Samples.FeatureLayerQuery.FeatureLayerQuery">
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition Height="auto" />
      <RowDefinition Height="*" />
    </Grid.RowDefinitions>
    <StackLayout Orientation="Vertical">
      <Entry x:Name="queryEntry" Text="New York"/>
      <Button Text="Query" Clicked="OnQueryClicked"/>
    </StackLayout>
    <esriUI:MapView x:Name="myMapView"  Grid.Row="1"/>
  </Grid>
</ContentPage>
// Copyright 2016 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: http://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.

using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Xamarin.Forms;
using Color = System.Drawing.Color;

namespace ArcGISRuntime.Samples.FeatureLayerQuery
{
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Feature layer query",
        category: "Data",
        description: "Find features in a feature table which match an SQL query.",
        instructions: "Input the name of a U.S. state into the text field. When you tap the button, a query is performed and the matching features are highlighted or an error is returned.",
        tags: new[] { "query", "search" })]
    public partial class FeatureLayerQuery : ContentPage
    {
        // Create reference to service of US States
        private string _statesUrl = "https://sampleserver6.arcgisonline.com/arcgis/rest/services/USA/MapServer/2";

        // Create globally available feature table for easy referencing
        private ServiceFeatureTable _featureTable;

        // Create globally available feature layer for easy referencing
        private FeatureLayer _featureLayer;

        public FeatureLayerQuery()
        {
            InitializeComponent();

            // Create the UI, setup the control references and execute initialization
            Initialize();
        }

        private void Initialize()
        {
            // Create new Map with basemap
            Map myMap = new Map(Basemap.CreateTopographic());

            // Create and set initial map location
            MapPoint initialLocation = new MapPoint(
                -11000000, 5000000, SpatialReferences.WebMercator);
            myMap.InitialViewpoint = new Viewpoint(initialLocation, 100000000);

            // Create feature table using a url
            _featureTable = new ServiceFeatureTable(new Uri(_statesUrl));

            // Create feature layer using this feature table
            _featureLayer = new FeatureLayer(_featureTable)
            {
                // Set the Opacity of the Feature Layer
                Opacity = 0.6,
                // Work around service setting
                MaxScale = 10
            };

            // Create a new renderer for the States Feature Layer.
            SimpleLineSymbol lineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.Black, 1);
            SimpleFillSymbol fillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, Color.Transparent, lineSymbol);

            // Set States feature layer renderer
            _featureLayer.Renderer = new SimpleRenderer(fillSymbol);

            // Add feature layer to the map
            myMap.OperationalLayers.Add(_featureLayer);

            // Set the selection color
            myMapView.SelectionProperties.Color = Color.Cyan;

            // Assign the map to the MapView
            myMapView.Map = myMap;
        }

        private async void OnQueryClicked(object sender, EventArgs e)
        {
            // Remove any previous feature selections that may have been made
            _featureLayer.ClearSelection();

            // Begin query process
            await QueryStateFeature(queryEntry.Text);
        }

        private async Task QueryStateFeature(string stateName)
        {
            try
            {
                // Create a query parameters that will be used to Query the feature table
                QueryParameters queryParams = new QueryParameters();

                // Trim whitespace on the state name to prevent broken queries
                string formattedStateName = stateName.Trim().ToUpper();

                // Construct and assign the where clause that will be used to query the feature table
                queryParams.WhereClause = "upper(STATE_NAME) LIKE '%" + formattedStateName + "%'";

                // Query the feature table
                FeatureQueryResult queryResult = await _featureTable.QueryFeaturesAsync(queryParams);

                // Cast the QueryResult to a List so the results can be interrogated.
                List<Feature> features = queryResult.ToList();

                if (features.Any())
                {
                    // Create an envelope.
                    EnvelopeBuilder envBuilder = new EnvelopeBuilder(SpatialReferences.WebMercator);

                    // Loop over each feature from the query result.
                    foreach (Feature feature in features)
                    {
                        // Add the extent of each matching feature to the envelope.
                        envBuilder.UnionOf(feature.Geometry.Extent);

                        // Select each feature.
                        _featureLayer.SelectFeature(feature);
                    }

                    // Zoom to the extent of the selected feature(s).
                    await myMapView.SetViewpointGeometryAsync(envBuilder.ToGeometry(), 50);
                }
                else
                {
                    await Application.Current.MainPage.DisplayAlert("State Not Found!", "Add a valid state name.", "OK");
                }
            }
            catch (Exception)
            {
                await Application.Current.MainPage.DisplayAlert("Sample error", "An error occurred", "OK");
            }
        }
    }
}