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 identifyLayer(featureLayer, mouseEvent.x(), mouseEvent.y(), tolerance, returnPopupsOnly, maxResults) on the map view.
  4. 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

FeatureLayerSelection.cppFeatureLayerSelection.cppFeatureLayerSelection.hFeatureLayerSelection.qml
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// [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;
}

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