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
To show custom labels on a feature layer:
Create a ServiceFeatureTable using a feature service URL.
Create a FeatureLayer from the service feature table.
Create an ArcadeLabelExpression for the label definition.
You can use fields of the feature by using $feature.field_name in the expression.
Create a TextSymbol to control how the label text is styled.
Create a LabelDefinition by passing in the ArcadeLabelExpression and TextSymbol.
Add the definition to the feature layer with featureLayer.labelDefinitions().append(labelDefinition) .
Lastly, enable labels on the layer using featureLayer.setLabelsEnabled().
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// [WriteFile Name=ShowLabelsOnLayers, Category=DisplayInformation]// [Legal]// 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.// [Legal]#ifdef PCH_BUILD#include"pch.hpp"#endif// PCH_BUILD#include"ShowLabelsOnLayers.h"#include"ArcadeLabelExpression.h"#include"FeatureLayer.h"#include"LabelDefinition.h"#include"Map.h"#include"MapQuickView.h"#include"ServiceFeatureTable.h"#include"TextSymbol.h"#include"MapTypes.h"#include"Error.h"#include"TaskWatcher.h"#include"LayerListModel.h"#include"LabelDefinitionListModel.h"#include"SymbolTypes.h"#include"Envelope.h"#include"SpatialReference.h"#include"Point.h"#include"Viewpoint.h"usingnamespace Esri::ArcGISRuntime;
ShowLabelsOnLayers::ShowLabelsOnLayers(QQuickItem* parent /* = nullptr */):
QQuickItem(parent)
{
}
voidShowLabelsOnLayers::init(){
// Register the map view for QML qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
qmlRegisterType<ShowLabelsOnLayers>("Esri.Samples", 1, 0, "ShowLabelsOnLayersSample");
}
voidShowLabelsOnLayers::componentComplete(){
QQuickItem::componentComplete();
// find QML MapView component m_mapView = findChild<MapQuickView*>("mapView");
// Create a map using the light gray basemap m_map = newMap(BasemapStyle::ArcGISLightGray, this);
// Create a feature layer ServiceFeatureTable* featureTable = newServiceFeatureTable(QUrl("https://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/USA_115th_Congressional_Districts/FeatureServer/0"), this);
FeatureLayer* featureLayer = newFeatureLayer(featureTable, this);
connect(featureLayer, &FeatureLayer::doneLoading, this, [this, featureLayer](const Error& e)
{
if (!e.isEmpty())
return;
m_mapView->setViewpoint(Viewpoint(featureLayer->fullExtent().center(), 56759600));
});
m_map->operationalLayers()->append(featureLayer);
// Apply labels to the feature layer LabelDefinition* republicanLabelDef = createRepublicanLabelDefinition();
LabelDefinition* democratLabelDef = createDemocratLabelDefinition();
featureLayer->labelDefinitions()->append(republicanLabelDef);
featureLayer->labelDefinitions()->append(democratLabelDef);
featureLayer->setLabelsEnabled(true);
// Set map to map view m_mapView->setViewpointCenter(Point(-10846309.950860, 4683272.219411, SpatialReference::webMercator()), 20000000);
m_mapView->setMap(m_map);
}
LabelDefinition* ShowLabelsOnLayers::createRepublicanLabelDefinition(){
// This particular LabelDefinition will have the following characteristics:// (1) The 'ArcadeLabelExpression' defines that the label text displayed comes from the fields 'NAME',// the first letter of PARTY' (R or D), and 'CDFIPS' in the feature service in the format:// Firstname Lastname (R)// District #// (2) The 'TextSymbol' for the labeled text will be red with a white halo centered in the target polygon.// (3) The 'where' clause of the 'LabelDefinition' restricts the labels to data from Republican districts. ArcadeLabelExpression* republicanArcadeLabelExpression = newArcadeLabelExpression("$feature.NAME + ' (' + left($feature.PARTY,1) + ')\\nDistrict ' + $feature.CDFIPS", this);
TextSymbol* republicanTextSymbol = newTextSymbol(this);
republicanTextSymbol->setSize(11);
republicanTextSymbol->setColor(Qt::red);
republicanTextSymbol->setHaloColor(Qt::white);
republicanTextSymbol->setHaloWidth(2);
republicanTextSymbol->setHorizontalAlignment(HorizontalAlignment::Center);
republicanTextSymbol->setVerticalAlignment(VerticalAlignment::Middle);
LabelDefinition* republicanLabelDefinition = newLabelDefinition(republicanArcadeLabelExpression, republicanTextSymbol, this);
republicanLabelDefinition->setWhereClause("PARTY = 'Republican'");
return republicanLabelDefinition;
}
LabelDefinition* ShowLabelsOnLayers::createDemocratLabelDefinition(){
// This particular LabelDefinition will have the following characteristics:// (1) The 'ArcadeLabelExpression' defines that the label text displayed comes from the fields 'NAME',// the first letter of PARTY' (R or D), and 'CDFIPS' in the feature service in the format:// Firstname Lastname (D)// District #// (2) The 'TextSymbol' for the labeled text will be blue with a white halo centered in the target polygon.// (3) The 'where' clause of the 'LabelDefinition' restricts the labels to data from Democrat districts. ArcadeLabelExpression* democratArcadeLabelExpression = newArcadeLabelExpression("$feature.NAME + ' (' + left($feature.PARTY,1) + ')\\nDistrict ' + $feature.CDFIPS", this);
TextSymbol* democratTextSymbol = newTextSymbol(this);
democratTextSymbol->setSize(11);
democratTextSymbol->setColor(Qt::blue);
democratTextSymbol->setHaloColor(Qt::white);
democratTextSymbol->setHaloWidth(2);
democratTextSymbol->setHorizontalAlignment(HorizontalAlignment::Center);
democratTextSymbol->setVerticalAlignment(VerticalAlignment::Middle);
LabelDefinition* democratLabelDefinition = newLabelDefinition(democratArcadeLabelExpression, democratTextSymbol, this);
democratLabelDefinition->setWhereClause("PARTY = 'Democrat'");
return democratLabelDefinition;
}