ShowLabelsOnLayer.cs

// 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.ShowLabelsOnLayer
{
    [Register("ShowLabelsOnLayer")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        "Show labels on layer",
        "Layers",
        "Show labels on a feature layer using a JSON label definition.",
        "The labeling of the names on the US Highways layer is accomplished by supplying a JSON string to the FeatureLayer's LabelDefinition. The JSON is based on the new ArcGIS web map specification.",
        "")]
    public class ShowLabelsOnLayer : UIViewController
    {
        // Hold a reference to the MapView.
        private MapView _myMapView;

        // Help regarding the Json syntax for defining the LabelDefinition.FromJson syntax can be found here:
        // https://developers.arcgis.com/web-map-specification/objects/labelingInfo/
        private const string RedLabelJson =
            @"{
                    ""labelExpressionInfo"":{""expression"":""$feature.NAME + ' (' + left($feature.PARTY,1) + ')\\nDistrict' + $feature.CDFIPS""},
                    ""labelPlacement"":""esriServerPolygonPlacementAlwaysHorizontal"",
                    ""where"":""PARTY = 'Republican'"",
                    ""symbol"":
                        { 
                            ""angle"":0,
                            ""backgroundColor"":[0,0,0,0],
                            ""borderLineColor"":[0,0,0,0],
                            ""borderLineSize"":0,
                            ""color"":[255,0,0,255],
                            ""font"":
                                {
                                    ""decoration"":""none"",
                                    ""size"":10,
                                    ""style"":""normal"",
                                    ""weight"":""normal""
                                },
                            ""haloColor"":[255,255,255,255],
                            ""haloSize"":2,
                            ""horizontalAlignment"":""center"",
                            ""kerning"":false,
                            ""type"":""esriTS"",
                            ""verticalAlignment"":""middle"",
                            ""xoffset"":0,
                            ""yoffset"":0
                        }
               }";

        private const string BlueLabelJson =
            @"{
                    ""labelExpressionInfo"":{""expression"":""$feature.NAME + ' (' + left($feature.PARTY,1) + ')\\nDistrict' + $feature.CDFIPS""},
                    ""labelPlacement"":""esriServerPolygonPlacementAlwaysHorizontal"",
                    ""where"":""PARTY = 'Democrat'"",
                    ""symbol"":
                        { 
                            ""angle"":0,
                            ""backgroundColor"":[0,0,0,0],
                            ""borderLineColor"":[0,0,0,0],
                            ""borderLineSize"":0,
                            ""color"":[0,0,255,255],
                            ""font"":
                                {
                                    ""decoration"":""none"",
                                    ""size"":10,
                                    ""style"":""normal"",
                                    ""weight"":""normal""
                                },
                            ""haloColor"":[255,255,255,255],
                            ""haloSize"":2,
                            ""horizontalAlignment"":""center"",
                            ""kerning"":false,
                            ""type"":""esriTS"",
                            ""verticalAlignment"":""middle"",
                            ""xoffset"":0,
                            ""yoffset"":0
                        }
               }";

        public ShowLabelsOnLayer()
        {
            Title = "Show labels on layer";
        }

        private async void Initialize()
        {
            // Create a map with a light gray canvas basemap.
            Map sampleMap = new Map(Basemap.CreateLightGrayCanvas());

            // Assign the map to the MapView.
            _myMapView.Map = sampleMap;

            // Define the URL string for the feature layer.
            const string layerUrl = "https://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/USA_115th_Congressional_Districts/FeatureServer/0";

            // Create a service feature table from the URL.
            ServiceFeatureTable featureTable = new ServiceFeatureTable(new Uri(layerUrl));

            // Create a feature layer from the service feature table.
            FeatureLayer districtFeatureLabel = new FeatureLayer(featureTable);

            // Add the feature layer to the operations layers collection of the map.
            sampleMap.OperationalLayers.Add(districtFeatureLabel);

            try
            {
                // Load the feature layer - this way we can obtain it's extent.
                await districtFeatureLabel.LoadAsync();

                // Zoom the map view to the extent of the feature layer.
                await _myMapView.SetViewpointCenterAsync(new MapPoint(-10846309.950860, 4683272.219411, SpatialReferences.WebMercator), 20000000);

                // Create a label definition from the JSON string. 
                LabelDefinition redLabelDefinition = LabelDefinition.FromJson(RedLabelJson);
                LabelDefinition blueLabelDefinition = LabelDefinition.FromJson(BlueLabelJson);

                // Add the label definition to the feature layer's label definition collection.
                districtFeatureLabel.LabelDefinitions.Add(redLabelDefinition);
                districtFeatureLabel.LabelDefinitions.Add(blueLabelDefinition);

                // Enable the visibility of labels to be seen.
                districtFeatureLabel.LabelsEnabled = true;
            }
            catch (Exception e)
            {
                new UIAlertView("Error", e.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }

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

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

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

            // Add the views.
            View.AddSubviews(_myMapView);

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