Show labels on layer

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Display custom labels on a feature layer.

Image of show labels on layer

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 streets 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(jsonString).
  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

MainActivity.java
                                                                                                                                         
/*
 * 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.arcgisruntime.showlabelsonlayer;

import java.util.Arrays;

import android.graphics.Color;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;
import com.esri.arcgisruntime.ArcGISRuntimeEnvironment;
import com.esri.arcgisruntime.arcgisservices.LabelDefinition;
import com.esri.arcgisruntime.data.ServiceFeatureTable;
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.Viewpoint;
import com.esri.arcgisruntime.mapping.view.MapView;
import com.esri.arcgisruntime.symbology.TextSymbol;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import com.google.gson.JsonPrimitive;

public class MainActivity extends AppCompatActivity {

  private static final String TAG = MainActivity.class.getSimpleName();

  private MapView mMapView;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // authentication with an API key or named user is required to access basemaps and other
    // location services
    ArcGISRuntimeEnvironment.setApiKey(BuildConfig.API_KEY);

    // create a map view and set a map
    mMapView = findViewById(R.id.mapView);
    ArcGISMap map = new ArcGISMap(BasemapStyle.ARCGIS_LIGHT_GRAY);
    mMapView.setMap(map);

    // create a feature layer from an online feature service of US Congressional Districts
    ServiceFeatureTable serviceFeatureTable = new ServiceFeatureTable(getString(R.string.congressional_districts_url));
    FeatureLayer featureLayer = new FeatureLayer(serviceFeatureTable);
    map.getOperationalLayers().add(featureLayer);

    // zoom to the layer when it's done loading
    featureLayer.addDoneLoadingListener(() -> {
      if (featureLayer.getLoadStatus() == LoadStatus.LOADED) {
        // set viewpoint to feature layer extent
        mMapView.setViewpointAsync(new Viewpoint(featureLayer.getFullExtent()));
      } else {
        String error = "Error loading feature layer :" + featureLayer.getLoadError().getCause();
        Toast.makeText(this, error, Toast.LENGTH_LONG).show();
        Log.e(TAG, error);
      }
    });

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

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

    // construct the label definition json
    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", JsonParser.parseString(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", JsonParser.parseString(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);
  }

  @Override
  protected void onPause() {
    mMapView.pause();
    super.onPause();
  }

  @Override
  protected void onResume() {
    super.onResume();
    mMapView.resume();
  }

  @Override
  protected void onDestroy() {
    mMapView.dispose();
    super.onDestroy();
  }
}