Show labels on layer

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Sample viewer app

Display custom labels on a feature layer.

Image of show labels on layers

Use case

Labeling features is useful to visually display a key piece of information or attribute of a feature on a map. For example, you may want to label rivers or street with their names.

How to use the sample

Pan and zoom around the United States. Labels for congressional districts will be shown in red for Republican districts and blue for Democrat districts. Notice how labels pop into view as you zoom in.

How it works

  1. Create a ServiceFeatureTable using a feature service URL.
  2. Create a FeatureLayer from the service feature table.
  3. Create a TextSymbol to use for displaying the label text.
  4. Create a JSON string for the label definition.

    • Set the "LabelExpressionInfo.expression" key to express what the text the label should display. You can use fields of the feature by using $feature.field_name in the expression.
    • To use the text symbol, set the "symbol" key to the symbol's JSON representation using textSymbol.toJson().
  5. Create a label definition from the JSON using LabelDefinition.fromJson(json).
  6. Add the definition to the feature layer with featureLayer.getLabelDefinitions().add(labelDefinition).
  7. Lastly, enable labels on the layer using featureLayer.setLabelsEnabled().

Relevant API

  • FeatureLayer
  • LabelDefinition
  • TextSymbol

About the data

This sample uses the USA 116th Congressional Districts feature layer hosted on ArcGIS Online.

Additional information

Help regarding the JSON syntax for defining the LabelDefinition.FromJson syntax can be found in labeling info in the Web map specification.

Tags

attribute, deconfliction, label, labeling, string, symbol, text, visualization

Sample Code

ShowLabelsOnLayerSample.java
                                                                                                                                                                     
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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.
 */

package com.esri.samples.show_labels_on_layer;

import java.util.Arrays;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import com.google.gson.JsonPrimitive;

import com.esri.arcgisruntime.ArcGISRuntimeEnvironment;
import com.esri.arcgisruntime.arcgisservices.LabelDefinition;
import com.esri.arcgisruntime.data.ServiceFeatureTable;
import com.esri.arcgisruntime.geometry.Point;
import com.esri.arcgisruntime.geometry.SpatialReferences;
import com.esri.arcgisruntime.layers.FeatureLayer;
import com.esri.arcgisruntime.loadable.LoadStatus;
import com.esri.arcgisruntime.mapping.ArcGISMap;
import com.esri.arcgisruntime.mapping.BasemapStyle;
import com.esri.arcgisruntime.mapping.view.MapView;
import com.esri.arcgisruntime.symbology.TextSymbol;

public class ShowLabelsOnLayerSample extends Application {

  private MapView mapView;

  @Override
  public void start(Stage stage) {

    try {
      // create stack pane and application scene
      StackPane stackPane = new StackPane();
      Scene scene = new Scene(stackPane);

      // size the stage, add a title, and set scene to stage
      stage.setTitle("Show Labels on Layer Sample");
      stage.setHeight(700);
      stage.setWidth(800);
      stage.setScene(scene);
      stage.show();

      // authentication with an API key or named user is required to access basemaps and other location services
      String yourAPIKey = System.getProperty("apiKey");
      ArcGISRuntimeEnvironment.setApiKey(yourAPIKey);

      // create a map with the light gray basemap style
      ArcGISMap map = new ArcGISMap(BasemapStyle.ARCGIS_LIGHT_GRAY);

      // create a map view and set the map to it
      mapView = new MapView();
      mapView.setMap(map);

      // set the initial viewpoint near the center of the US
      mapView.setViewpointCenterAsync(new Point(-10846309.950860, 4683272.219411, SpatialReferences.getWebMercator()), 20000000);

      // create a feature layer from an online feature service of US Congressional Districts
      String serviceUrl = "https://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/USA_116th_Congressional_Districts/FeatureServer/0";
      ServiceFeatureTable serviceFeatureTable = new ServiceFeatureTable(serviceUrl);
      FeatureLayer featureLayer = new FeatureLayer(serviceFeatureTable);

      // add the feature layer to the map
      map.getOperationalLayers().add(featureLayer);

      // show alert if layer fails to load
      featureLayer.addDoneLoadingListener(() -> {
        if (featureLayer.getLoadStatus() != LoadStatus.LOADED) {
          new Alert(Alert.AlertType.ERROR, "Error loading Feature Layer.").show();
        }
      });

      // use red text with white halo for republican district labels
      TextSymbol republicanTextSymbol = new TextSymbol();
      republicanTextSymbol.setSize(10);
      republicanTextSymbol.setColor(0xFFFF0000);
      republicanTextSymbol.setHaloColor(0xFFFFFFFF);
      republicanTextSymbol.setHaloWidth(2);

      // use blue text with white halo for democrat district labels
      TextSymbol democratTextSymbol = new TextSymbol();
      democratTextSymbol.setSize(10);
      democratTextSymbol.setColor(0xFF0000FF);
      democratTextSymbol.setHaloColor(0xFFFFFFFF);
      democratTextSymbol.setHaloWidth(2);

      // construct a json label definition
      JsonObject json = new JsonObject();
      // use a custom label expression combining some of the feature's fields
      JsonObject expressionInfo = new JsonObject();
      expressionInfo.add("expression", new JsonPrimitive("$feature.NAME + \" (\" + left($feature.PARTY,1) + \")\\nDistrict \" + $feature.CDFIPS"));
      json.add("labelExpressionInfo", expressionInfo);
      // position the label in the center of the feature
      json.add("labelPlacement", new JsonPrimitive("esriServerPolygonPlacementAlwaysHorizontal"));

      // create a copy of the json with a custom where clause and symbol only for republican districts
      JsonObject republicanJson = json.deepCopy();
      republicanJson.add("where", new JsonPrimitive("PARTY = 'Republican'"));
      republicanJson.add("symbol", new JsonParser().parse(republicanTextSymbol.toJson()));

      // create a copy of the json with a custom where clause and symbol only for democrat districts
      JsonObject democratJson = json.deepCopy();
      democratJson.add("where", new JsonPrimitive("PARTY = 'Democrat'"));
      democratJson.add("symbol", new JsonParser().parse(democratTextSymbol.toJson()));

      // create label definitions from the JSON strings
      LabelDefinition republicanLabelDefinition = LabelDefinition.fromJson(republicanJson.toString());
      LabelDefinition democratLabelDefinition = LabelDefinition.fromJson(democratJson.toString());

      // add the definitions to the feature layer
      featureLayer.getLabelDefinitions().addAll(Arrays.asList(republicanLabelDefinition, democratLabelDefinition));
      featureLayer.getLabelDefinitions().add(democratLabelDefinition);

      // enable labels
      featureLayer.setLabelsEnabled(true);

      // add the map view to stack pane
      stackPane.getChildren().add(mapView);

    } catch (Exception e) {
      // on any error, display stack trace
      e.printStackTrace();
    }
  }

  /**
   * Stops and releases all resources used in application.
   */
  @Override
  public void stop() {

    // release resources when the application closes
    if (mapView != null) {
      mapView.dispose();
    }
  }

  /**
   * Opens and runs application.
   *
   * @param args arguments passed to this application
   */
  public static void main(String[] args) {

    Application.launch(args);
  }
}

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