Query feature count and extent

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 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 // 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 ArcGIS import SwiftUI  struct QueryFeatureCountAndExtentView: View {  /// The view model for the sample.  @StateObject private var model = Model()   /// The currently selected state abbreviation.  @State private var selectedState: String?   /// A Boolean value indicating whether the feature count bar is showing.  @State private var showFeatureCountBar = false   /// The error shown in the error alert.  @State private var error: Error?   /// The current viewpoint of the map.  @State private var viewpoint: Viewpoint?   /// The count of features within the current viewpoint.  @State private var featureCountResult: Int?   var body: some View {  MapViewReader { proxy in  MapView(map: model.map)  .onViewpointChanged(kind: .boundingGeometry) { newViewpoint in  // Update viewpoint when it changes.  viewpoint = newViewpoint  }  .task(id: selectedState) {  // Perform query and update the viewpoint when the selected state changes.  guard let state = selectedState else { return }  do {  if let combinedExtent = try await model.queryExtent(stateAbbreviation: state) {  await proxy.setViewpointGeometry(combinedExtent)  showFeatureCountBar = false  }  } catch {  self.error = error  }  selectedState = nil  }  }  .overlay(alignment: .top) {  if showFeatureCountBar {  Text("\(featureCountResult ?? 0) feature(s) in extent")  .frame(maxWidth: .infinity)  .padding(.vertical, 6)  .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)  .transition(.move(edge: .top))  }  }  .toolbar {  ToolbarItemGroup(placement: .bottomBar) {  // Menu to select a state.  Menu("Select State") {  ForEach(model.stateAbbreviations, id: \.self) { abbreviation in  Button {  selectedState = abbreviation  } label: {  Text(abbreviation)  }  }  }   // Button to count features within the visible extent.  Button("Count Features") {  Task {  do {  if let viewpoint = viewpoint {  featureCountResult = try await model.countFeaturesWithinExtent(extent: viewpoint.targetGeometry)  showFeatureCountBar = true  }  } catch {  self.error = error  }  }  }  }  }  .errorAlert(presentingError: $error)  } }  private extension QueryFeatureCountAndExtentView {  /// The view model for the sample.  @MainActor  class Model: ObservableObject {  /// The map with a basemap and initial viewpoint.  let map: Map = {  let map = Map(basemapStyle: .arcGISDarkGray)  map.initialViewpoint = Viewpoint(  center: Point(x: -11e6, y: 5e6, spatialReference: .webMercator),  scale: 9e7  )  return map  }()   /// The layer that displays features on the map.  private let featureLayer: FeatureLayer   /// The table for querying features from a server.  private let featureTable: ServiceFeatureTable   /// The list of state abbreviations for selection.  let stateAbbreviations = [  "AL", "AK", "AZ", "AR", "CA", "CO", "CT", "DE", "DC", "FL", "GA", "HI",  "ID", "IL", "IN", "IA", "KS", "KY", "LA", "ME", "MD", "MA", "MI", "MN",  "MS", "MO", "MT", "NE", "NV", "NH", "NJ", "NM", "NY", "NC", "ND", "OH",  "OK", "OR", "PA", "RI", "SC", "SD", "TN", "TX", "UT", "VT", "VA", "WA",  "WV", "WI", "WY"  ]   init() {  featureTable = ServiceFeatureTable(url: .medicareHospitalSpendLayer)  featureLayer = FeatureLayer(featureTable: featureTable)  map.addOperationalLayer(featureLayer)  }   /// Queries the extent for the specified state.  /// - Parameter stateAbbreviation: The state abbreviation to query.  /// - Returns: The combined extent of the queried features or `nil` if no features are found.  /// - Throws: An error if the query fails.  func queryExtent(stateAbbreviation: String) async throws -> Envelope? {  guard !stateAbbreviation.isEmpty else { return nil }  featureLayer.clearSelection()  let queryParameters = QueryParameters()  queryParameters.whereClause = "State LIKE '%\(stateAbbreviation)%'"   let queryResult = try await featureTable.queryFeatures(using: queryParameters)  let queryResultFeatures = Array(queryResult.features())   if !queryResultFeatures.isEmpty {  return GeometryEngine.combineExtents(  of: queryResultFeatures.compactMap(\.geometry)  )  } else {  return nil  }  }   /// Counts the number of features within the specified extent.  /// - Parameter extent: The geometry defining the extent to query.  /// - Returns: The count of features within the specified extent.  /// - Throws: An error if the count operation fails.  func countFeaturesWithinExtent(extent: Geometry) async throws -> Int {  let queryParameters = QueryParameters()  queryParameters.geometry = extent  queryParameters.spatialRelationship = .intersects  return try await featureLayer.featureTable!.queryFeatureCount(  using: queryParameters  )  }  } }  private extension URL {  /// The URL for the Medicare Hospital Spending layer service.  static var medicareHospitalSpendLayer: URL {  URL(string: "https://services1.arcgis.com/4yjifSiIG17X0gW4/arcgis/rest/services/Medicare_Hospital_Spending_per_Patient/FeatureServer/0")!  } }  #Preview {  QueryFeatureCountAndExtentView() }