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.
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.
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/*
* 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
classMainActivity : AppCompatActivity() {
// set up data binding for the activityprivateval activityMainBinding: ActivityMainBinding by lazy {
DataBindingUtil.setContentView(this, R.layout.activity_main)
}
privateval mapView by lazy {
activityMainBinding.mapView
}
overridefunonCreate(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 styleval map = ArcGISMap(BasemapStyle.ArcGISLightGray)
// create a service feature table from an online feature service of// US Congressional Districtsval serviceFeatureTable =
ServiceFeatureTable(getString(R.string.congressional_districts_url))
// create the feature layer from the service feature tableval 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:${it.message}")
}
// zoom to the layer when it's done loading featureLayer.fullExtent?.let { extent ->
mapView.setViewpoint(Viewpoint(extent))
}
}
// create label definitions for the different party type attribute in the feature serviceval republicanLabelDefinition = createLabelDefinition("Republican", Color.red)
val democraticLabelDefinition = createLabelDefinition("Democrat", Color.blue)
featureLayer.apply {
// add the label definitions to the feature layer labelDefinitions.addAll(
listOf(
republicanLabelDefinition,
democraticLabelDefinition
)
)
// enable the labels labelsEnabled = true }
}
/**
* Creates and returns a [LabelDefinition] for the given party [name] attribute
* with the [labelColor]
*/privatefuncreateLabelDefinition(
name: String,
labelColor: Color ): LabelDefinition {
// create a text symbol for styling the labelval textSymbol = TextSymbol().apply {
color = labelColor
size = 12f haloColor = Color.white
haloWidth = 2f }
// create a arcade label expression for the label textval arcadeLabelExpression =
ArcadeLabelExpression(
"\$feature.NAME + \" (\" + left(\$feature.PARTY,1) " +
"+ \")\\nDistrict \" + \$feature.CDFIPS" )
// create and return a new label definition with the arcadeLabelExpression and textSymbolreturn LabelDefinition(arcadeLabelExpression, textSymbol).apply {
// set the label placement placement = LabelingPlacement.PolygonAlwaysHorizontal
// set the attribute name for which this label will be generated whereClause = "PARTY = '$name'" }
}
privatefunshowError(message: String) {
Log.e(localClassName, message)
Snackbar.make(mapView, message, Snackbar.LENGTH_SHORT).show()
}
}
/**
* Simple extension property that represents a blue color
*/privateval Color.Companion.blue get() = fromRgba(0, 0, 255)