Display custom labels on a feature 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
- Create a
ServiceFeatureTable
using a feature service URL. - Create a
FeatureLayer
from the service feature table. - Create a
TextSymbol
to use for displaying the label text. - Create an
ArcadeLabelExpression
for the label definition.- You can use fields of the feature by using
$feature.field_name
in the expression.
- You can use fields of the feature by using
- Create a new
LabelDefinition
from the arcade label expression and text symbol. - Add the definition to the feature layer with
featureLayer.labelDefinitions.add(labelDefinition)
. - Lastly, enable labels on the layer using
featureLayer.labelsEnabled
.
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 Arcade label expression script for defining a label definition can be found on the ArcGIS Developers site.
Tags
arcade, attribute, deconfliction, label, labeling, string, symbol, text, visualization
Sample Code
/*
* Copyright 2023 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.arcgismaps.sample.showlabelsonlayer
import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.lifecycleScope
import com.arcgismaps.ApiKey
import com.arcgismaps.Color
import com.arcgismaps.ArcGISEnvironment
import com.arcgismaps.arcgisservices.LabelingPlacement
import com.arcgismaps.data.ServiceFeatureTable
import com.arcgismaps.mapping.ArcGISMap
import com.arcgismaps.mapping.BasemapStyle
import com.arcgismaps.mapping.Viewpoint
import com.arcgismaps.mapping.labeling.ArcadeLabelExpression
import com.arcgismaps.mapping.labeling.LabelDefinition
import com.arcgismaps.mapping.layers.FeatureLayer
import com.arcgismaps.mapping.symbology.TextSymbol
import com.esri.arcgismaps.sample.showlabelsonlayer.databinding.ActivityMainBinding
import com.google.android.material.snackbar.Snackbar
import kotlinx.coroutines.launch
class MainActivity : AppCompatActivity() {
// set up data binding for the activity
private val activityMainBinding: ActivityMainBinding by lazy {
DataBindingUtil.setContentView(this, R.layout.activity_main)
}
private val mapView by lazy {
activityMainBinding.mapView
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// authentication with an API key or named user is
// required to access basemaps and other location services
ArcGISEnvironment.apiKey = ApiKey.create(BuildConfig.API_KEY)
lifecycle.addObserver(mapView)
// create a map with a light gray map style
val map = ArcGISMap(BasemapStyle.ArcGISLightGray)
// create a service feature table from an online feature service of
// US Congressional Districts
val serviceFeatureTable =
ServiceFeatureTable(getString(R.string.congressional_districts_url))
// create the feature layer from the service feature table
val featureLayer = FeatureLayer.createWithFeatureTable(serviceFeatureTable)
// add this feature layer to the map
map.operationalLayers.add(featureLayer)
// add the map to the mapview
mapView.map = map
lifecycleScope.launch {
// if the map load failed show an error and return
map.load().onFailure {
return@onFailure showError("Error loading map:${it.message}")
}
// if the feature layer load failed show an error and return
featureLayer.load().onFailure {
return@onFailure showError("Error loading feature layer:${it.message}")
}
// zoom to the layer when it's done loading
featureLayer.fullExtent?.let { extent ->
mapView.setViewpoint(Viewpoint(extent))
}
}
// create label definitions for the different party type attribute in the feature service
val republicanLabelDefinition = createLabelDefinition("Republican", Color.red)
val democraticLabelDefinition = createLabelDefinition("Democrat", Color.blue)
featureLayer.apply {
// add the label definitions to the feature layer
labelDefinitions.addAll(
listOf(
republicanLabelDefinition,
democraticLabelDefinition
)
)
// enable the labels
labelsEnabled = true
}
}
/**
* Creates and returns a [LabelDefinition] for the given party [name] attribute
* with the [labelColor]
*/
private fun createLabelDefinition(
name: String,
labelColor: Color
): LabelDefinition {
// create a text symbol for styling the label
val textSymbol = TextSymbol().apply {
color = labelColor
size = 12f
haloColor = Color.white
haloWidth = 2f
}
// create a arcade label expression for the label text
val arcadeLabelExpression =
ArcadeLabelExpression(
"\$feature.NAME + \" (\" + left(\$feature.PARTY,1) " +
"+ \")\\nDistrict \" + \$feature.CDFIPS"
)
// create and return a new label definition with the arcadeLabelExpression and textSymbol
return LabelDefinition(arcadeLabelExpression, textSymbol).apply {
// set the label placement
placement = LabelingPlacement.PolygonAlwaysHorizontal
// set the attribute name for which this label will be generated
whereClause = "PARTY = '$name'"
}
}
private fun showError(message: String) {
Log.e(localClassName, message)
Snackbar.make(mapView, message, Snackbar.LENGTH_SHORT).show()
}
}
/**
* Simple extension property that represents a blue color
*/
private val Color.Companion.blue get() = fromRgba(0, 0, 255)