Feature layer selection

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Select features in a feature layer.

screenshot

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

  1. Create a ServiceFeatureTable from a feature service URL.
  2. Create a FeatureLayer from the service feature table.
  3. Identify nearby features at the clicked location using identifyLayerAsync(featureLayer, mouseEvent.position(), tolerance, returnPopupsOnly, maxResults) on the map view.
  4. Select all identified features in the feature layer with selectFeatures(features).

Relevant API

  • Feature
  • FeatureLayer
  • ServiceFeatureTable

About the data

This sample uses the Gross Domestic Product, 1960-2016 feature service. Only the 2016 GDP values are shown.

Tags

features, layers, select, selection, tolerance

Sample Code

FeatureLayerSelection.cppFeatureLayerSelection.cppFeatureLayerSelection.hFeatureLayerSelection.qml
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// [WriteFile Name=FeatureLayerSelection, Category=Features]
// [Legal]
// Copyright 2022 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 "Envelope.h"
#include "Feature.h"
#include "FeatureLayer.h"
#include "IdentifyLayerResult.h"
#include "LayerListModel.h"
#include "Map.h"
#include "MapQuickView.h"
#include "MapTypes.h"
#include "ServiceFeatureTable.h"
#include "SpatialReference.h"
#include "Viewpoint.h"

#include <QFuture>
#include <QUuid>
#include <memory>

using namespace Esri::ArcGISRuntime;

FeatureLayerSelection::FeatureLayerSelection(QObject* parent /* = nullptr */):
  QObject(parent),
  m_map(new Map(BasemapStyle::ArcGISLightGray, this))
{
  m_map->setInitialViewpoint(Viewpoint(Envelope(-6603299.491810, 1679677.742046, 9002253.947487, 8691318.054732, SpatialReference::webMercator())));

  m_featureTable = new ServiceFeatureTable(QUrl("https://services1.arcgis.com/4yjifSiIG17X0gW4/arcgis/rest/services/GDP_per_capita_1960_2016/FeatureServer/0"), this);
  m_featureLayer = new FeatureLayer(m_featureTable, this);
  m_map->operationalLayers()->append(m_featureLayer);
}

FeatureLayerSelection::~FeatureLayerSelection() = default;

void FeatureLayerSelection::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<FeatureLayerSelection>("Esri.Samples", 1, 0, "FeatureLayerSelectionSample");
}

MapQuickView* FeatureLayerSelection::mapView() const
{
  return m_mapView;
}

QString FeatureLayerSelection::selectedFeatureText() const
{
  return m_selectedFeatureText;
}

// Set the view (created in QML)
void FeatureLayerSelection::setMapView(MapQuickView* mapView)
{
  if (!mapView || mapView == m_mapView)
    return;

  m_mapView = mapView;
  m_mapView->setMap(m_map);

  connectSignals();

  emit mapViewChanged();
}

//! [identify feature layer qml api snippet]
void FeatureLayerSelection::connectSignals()
{
  // 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;
    m_mapView->identifyLayerAsync(m_featureLayer, mouseEvent.position(), tolerance, returnPopupsOnly, maximumResults).then(this,
    [this](IdentifyLayerResult* result)
    {
      onIdentifyLayerCompleted_(result);
    });
  });
}

void FeatureLayerSelection::onIdentifyLayerCompleted_(IdentifyLayerResult* result)
{
  auto identifyResult = std::unique_ptr<IdentifyLayerResult>(result);

  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
  const qsizetype 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]

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