Select features in a feature layer.
Use case
Selecting features, whether by query or identify, can be an important step both in editing data and visualizing results. One possible use case would be to query a feature layer containing street furniture. A query might look for type "bench" and return a list of bench features contained in the features with an attribute of type bench. These might be selected for further editing (see FeatureQueryResult) or may just be highlighted visually.
How to use the sample
Click on a feature in the map. All features within a given tolerance (in pixels) of the click will be selected.
How it works
- Create a
ServiceFeatureTable
from a feature service URL. - Create a
FeatureLayer
from the service feature table. - Identify nearby features at the clicked location using
identifyLayer(featureLayer, mouseEvent.x(), mouseEvent.y(), tolerance, returnPopupsOnly, maxResults)
on the map view. - Select all identified features in the feature layer with
selectFeatures(features)
.
About the data
This sample uses the Gross Domestic Product, 1960-2016 feature service. Only the 2016 GDP values are shown.
Relevant API
- Feature
- FeatureLayer
- ServiceFeatureTable
Tags
features, layers, select, selection, tolerance
Sample Code
// [WriteFile Name=FeatureLayerSelection, Category=Features]
// [Legal]
// Copyright 2016 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 "FeatureLayerSelection.h"
#include "Map.h"
#include "MapQuickView.h"
#include "FeatureLayer.h"
#include "Basemap.h"
#include "SpatialReference.h"
#include "ServiceFeatureTable.h"
#include "Viewpoint.h"
#include "Envelope.h"
#include "Feature.h"
#include "GeoElement.h"
#include <QList>
#include <QString>
#include <QUrl>
#include <QMouseEvent>
#include <memory>
using namespace Esri::ArcGISRuntime;
FeatureLayerSelection::FeatureLayerSelection(QQuickItem* parent) :
QQuickItem(parent)
{
}
FeatureLayerSelection::~FeatureLayerSelection() = default;
void FeatureLayerSelection::init()
{
qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
qmlRegisterType<FeatureLayerSelection>("Esri.Samples", 1, 0, "FeatureLayerSelectionSample");
}
void FeatureLayerSelection::componentComplete()
{
QQuickItem::componentComplete();
// find QML MapView component
m_mapView = findChild<MapQuickView*>("mapView");
m_mapView->setWrapAroundMode(WrapAroundMode::Disabled);
// Create a map using the streets basemap
m_map = new Map(BasemapStyle::ArcGISLightGray, this);
m_map->setInitialViewpoint(Viewpoint(Envelope(-6603299.491810, 1679677.742046, 9002253.947487, 8691318.054732, SpatialReference::webMercator())));
// Set map to map view
m_mapView->setMap(m_map);
// create the feature table
m_featureTable = new ServiceFeatureTable(QUrl("https://services1.arcgis.com/4yjifSiIG17X0gW4/arcgis/rest/services/GDP_per_capita_1960_2016/FeatureServer/0"), this);
// create the feature layer using the feature table
m_featureLayer = new FeatureLayer(m_featureTable, this);
// add the feature layer to the map
m_map->operationalLayers()->append(m_featureLayer);
connectSignals();
}
void FeatureLayerSelection::connectSignals()
{
//! [identify feature layer qml api snippet]
// lambda expression for the mouse press event on the mapview... do an identify operation
connect(m_mapView, &MapQuickView::mouseClicked, this, [this](QMouseEvent& mouseEvent)
{
constexpr double tolerance = 22.0;
constexpr bool returnPopupsOnly = false;
constexpr int maximumResults = 1000;
const double screenX = mouseEvent.x();
const double screenY = mouseEvent.y();
m_mapView->identifyLayer(m_featureLayer, screenX, screenY, tolerance, returnPopupsOnly, maximumResults);
});
// once the identify is done
connect(m_mapView, &MapQuickView::identifyLayerCompleted, this, [this](QUuid, Esri::ArcGISRuntime::IdentifyLayerResult* rawIdentifyResult)
{
auto identifyResult = std::unique_ptr<IdentifyLayerResult>(rawIdentifyResult);
if (!identifyResult)
return;
// clear any existing selection
m_featureLayer->clearSelection();
// create a list to store the identified elements
QList<Feature*> identifiedFeatures;
for (int i = 0; i < identifyResult->geoElements().size(); i++)
{
GeoElement* element = identifyResult->geoElements().at(i);
if (nullptr != element)
{
// add the element to the list and take ownership of it.
Feature* feature = static_cast<Feature*>(element);
feature->setParent(this);
identifiedFeatures.append(feature);
}
}
// select the identified features
m_featureLayer->selectFeatures(identifiedFeatures);
// update the member with the number of selected features
int count = identifiedFeatures.length();
m_selectedFeatureText = count > 1 ? QString::number(count) + " features selected." : QString::number(count) + " feature selected.";
emit selectedFeatureTextChanged();
});
//! [identify feature layer qml api snippet]
}
QString FeatureLayerSelection::selectedFeatureText() const
{
return m_selectedFeatureText;
}