Query feature count and extent

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// Copyright 2018 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 System;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using UIKit;

namespace ArcGISRuntime.Samples.QueryFeatureCountAndExtent
{
    [Register("QueryFeatureCountAndExtent")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Query feature count and extent",
        category: "Analysis",
        description: "Zoom to features matching a query and count the features in the current visible extent.",
        instructions: "Use the button to zoom to the extent of the state specified (by abbreviation) in the textbox or use the button to count the features in the current extent.",
        tags: new[] { "count", "feature layer", "feature table", "features", "filter", "number", "query" })]
    public class QueryFeatureCountAndExtent : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UILabel _resultLabel;
        private UIBarButtonItem _countInExtentButton;
        private UIBarButtonItem _zoomToQueryButton;
        private UIAlertController _unionAlert;

        // URL to the feature service.
        private readonly Uri _medicareHospitalSpendLayer =
            new Uri("https://services1.arcgis.com/4yjifSiIG17X0gW4/arcgis/rest/services/Medicare_Hospital_Spending_per_Patient/FeatureServer/0");

        // Feature table to query.
        private ServiceFeatureTable _featureTable;

        public QueryFeatureCountAndExtent()
        {
            Title = "Query feature count and extent";
        }

        private async void Initialize()
        {
            // Create the map with a basemap.
            Map myMap = new Map(BasemapStyle.ArcGISDarkGray);

            // Create the feature table from the service URL.
            _featureTable = new ServiceFeatureTable(_medicareHospitalSpendLayer);

            // Create the feature layer from the table.
            FeatureLayer myFeatureLayer = new FeatureLayer(_featureTable);

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

            try
            {
                // Wait for the feature layer to load.
                await myFeatureLayer.LoadAsync();

                // Set the map initial extent to the extent of the feature layer.
                myMap.InitialViewpoint = new Viewpoint(myFeatureLayer.FullExtent);

                // Add the map to the MapView.
                _myMapView.Map = myMap;
            }
            catch (Exception e)
            {
                new UIAlertView("Error", e.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }

        private async void ZoomToFeature(string query)
        {
            // Create the query parameters.
            QueryParameters queryStates = new QueryParameters {WhereClause = $"upper(State) LIKE '%{query.ToUpper()}%'"};

            try
            {
                // Get the extent from the query.
                Envelope resultExtent = await _featureTable.QueryExtentAsync(queryStates);

                // Return if there is no result (might happen if query is invalid).
                if (resultExtent?.SpatialReference == null)
                {
                    return;
                }

                // Create a viewpoint from the extent.
                Viewpoint resultViewpoint = new Viewpoint(resultExtent);

                // Zoom to the viewpoint.
                await _myMapView.SetViewpointAsync(resultViewpoint);

                // Update the UI.
                _resultLabel.Text = $"Zoomed to features in {query}";
            }
            catch (Exception ex)
            {
                new UIAlertView("Error", ex.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }

        private void ZoomToQuery_Click(object sender, EventArgs e)
        {
            // Prompt for the type of convex hull to create.
            if (_unionAlert == null)
            {
                _unionAlert = UIAlertController.Create("Query features", "Enter a state abbreviation (e.g. CA)", UIAlertControllerStyle.Alert);
                _unionAlert.AddTextField(field => field.Placeholder = "e.g. CA");
                _unionAlert.AddAction(UIAlertAction.Create("Submit query", UIAlertActionStyle.Default, action => ZoomToFeature(_unionAlert.TextFields[0].Text)));
                _unionAlert.AddAction(UIAlertAction.Create("Cancel", UIAlertActionStyle.Cancel, null));
            }

            // Show the alert.
            PresentViewController(_unionAlert, true, null);
        }

        private async void CountFeatures_Click(object sender, EventArgs e)
        {
            // Get the current visible extent.
            Geometry currentExtent = _myMapView.GetCurrentViewpoint(ViewpointType.BoundingGeometry).TargetGeometry;

            // Create the query parameters.
            QueryParameters queryCityCount = new QueryParameters
            {
                Geometry = currentExtent,
                // Specify the interpretation of the Geometry query parameters.
                SpatialRelationship = SpatialRelationship.Intersects
            };

            try
            {
                // Get the count of matching features.
                long count = await _featureTable.QueryFeatureCountAsync(queryCityCount);

                // Update the UI.
                _resultLabel.Text = $"{count} features in extent";
            }
            catch (Exception ex)
            {
                new UIAlertView("Error", ex.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            Initialize();
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView {BackgroundColor = ApplicationTheme.BackgroundColor};

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _zoomToQueryButton = new UIBarButtonItem();
            _zoomToQueryButton.Title = "Zoom to query";

            _countInExtentButton = new UIBarButtonItem();
            _countInExtentButton.Title = "Count in extent";

            UIToolbar toolbar = new UIToolbar();
            toolbar.TranslatesAutoresizingMaskIntoConstraints = false;
            toolbar.Items = new[]
            {
                _countInExtentButton,
                new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace),
                _zoomToQueryButton
            };

            _resultLabel = new UILabel
            {
                Text = "Press 'Zoom to query' to begin.",
                BackgroundColor = UIColor.FromWhiteAlpha(0f, .6f),
                TextColor = UIColor.White,
                TextAlignment = UITextAlignment.Center,
                TranslatesAutoresizingMaskIntoConstraints = false
            };

            // Add the views.
            View.AddSubviews(_myMapView, toolbar, _resultLabel);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]
            {
                _myMapView.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _myMapView.BottomAnchor.ConstraintEqualTo(toolbar.TopAnchor),

                toolbar.BottomAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.BottomAnchor),
                toolbar.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                toolbar.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                _resultLabel.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _resultLabel.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _resultLabel.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _resultLabel.HeightAnchor.ConstraintEqualTo(40)
            });
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _zoomToQueryButton.Clicked += ZoomToQuery_Click;
            _countInExtentButton.Clicked += CountFeatures_Click;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _zoomToQueryButton.Clicked -= ZoomToQuery_Click;
            _countInExtentButton.Clicked -= CountFeatures_Click;

            // Remove the reference to the alert, preventing a memory leak.
            _unionAlert = null;
        }
    }
}