Show labels on layers

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
// 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.

import UIKit
import ArcGIS

class ShowLabelsOnLayersViewController: UIViewController {
    @IBOutlet private weak var mapView: AGSMapView! {
        didSet {
            mapView.map = makeMap()
            // Set the map viewpoint to show the layer.
            mapView.setViewpointCenter(AGSPoint(x: -10840000, y: 4680000, spatialReference: .webMercator()), scale: 20000000)
        }
    }

    /// Make the map and add the feature layer.
    private func makeMap() -> AGSMap {
        // Create a map with a light gray canvas basemap.
        let map = AGSMap(basemapStyle: .arcGISLightGrayBase)
        // A URL for a feature service layer.
        let featureTableURL = URL(string: "https://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/USA_Congressional_Districts_analysis/FeatureServer/0")!

        // Create a feature table from the URL.
        let featureTable = AGSServiceFeatureTable(url: featureTableURL)
        // Create a feature layer from the table.
        let featureLayer = AGSFeatureLayer(featureTable: featureTable)
        // Add the layer to the map.
        map.operationalLayers.add(featureLayer)
        addLabels(to: featureLayer)

        return map
    }

    /// Add labels to the layer.
    private func addLabels(to layer: AGSFeatureLayer) {
        // Turn on labeling.
        layer.labelsEnabled = true

        // Create label definitions for the two groups.
        let demDefinition = makeLabelDefinition(party: "Democrat", color: .blue)
        let repDefinition = makeLabelDefinition(party: "Republican", color: .red)

        // Add the label definitions to the layer.
        layer.labelDefinitions.addObjects(from: [demDefinition, repDefinition])
    }

    /// Creates a label definition for the given PARTY field value and color.
    private func makeLabelDefinition(party: String, color: UIColor) -> AGSLabelDefinition {
        // The styling for the label.
        let textSymbol = AGSTextSymbol()
        textSymbol.size = 12
        textSymbol.haloColor = .white
        textSymbol.haloWidth = 2
        textSymbol.color = color

        // An SQL WHERE statement for filtering the features this label applies to.
        let whereStatement = "PARTY = '\(party)'"
        // An expression that specifies the content of the label using the table's attributes.
        let expression = "$feature.NAME + ' (' + left($feature.PARTY,1) + ')\\nDistrict' + $feature.CDFIPS"
        // Make an arcade label expression.
        let arcadeLabelExpression = AGSArcadeLabelExpression(arcadeString: expression)
        let labelDefinition = AGSLabelDefinition(labelExpression: arcadeLabelExpression, textSymbol: textSymbol)
        labelDefinition.placement = .polygonAlwaysHorizontal
        labelDefinition.whereClause = whereStatement
        return labelDefinition
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add the source code button item to the right of navigation bar.
        (navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["ShowLabelsOnLayersViewController"]
    }
}