Identify layers

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Sample viewer app

Identify features in all layers in a map.

screenshot

Use case

IdentifyLayers allows users to tap on a map, returning features at that location across multiple layers. Because some layer types have sublayers, the sample recursively counts results for sublayers within each layer.

How to use the sample

Tap to identify features. An alert will show all layers with features under the cursor, as well as a layer count.

How it works

  1. The tapped position is passed to MapView::identifyLayers
  2. For each IdentifyLayerResult in the results, features are counted.
    • Note: there is one identify result per layer with matching features; if the feature count is 0, that means a sublayer contains the matching features.

Relevant API

  • IdentifyLayerResult
  • IdentifyLayerResult::layerContent::name
  • IdentifyLayerResult::sublayerResults
  • MapView::identifyLayers

Additional information

The GeoView supports two methods of identify: identifyLayer(), which identifies features within a specific layer and identifyLayers(), which identifies features for all layers in the current view.

Tags

identify, recursion, recursive, sublayers

Sample Code

IdentifyLayers.cppIdentifyLayers.cppIdentifyLayers.hIdentifyLayers.qml
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// [WriteFile Name=IdentifyLayers, Category=Maps]
// [Legal]
// Copyright 2017 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 "IdentifyLayers.h"

#include "Map.h"
#include "MapQuickView.h"
#include "Basemap.h"
#include "ArcGISMapImageLayer.h"
#include "ArcGISMapImageSublayer.h"
#include "FeatureLayer.h"
#include "ServiceFeatureTable.h"
#include "Viewpoint.h"
#include "Point.h"
#include "IdentifyLayerResult.h"

using namespace Esri::ArcGISRuntime;

IdentifyLayers::IdentifyLayers(QQuickItem* parent /* = nullptr */):
  QQuickItem(parent)
{
}

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

void IdentifyLayers::componentComplete()
{
  QQuickItem::componentComplete();

  // find QML MapView component
  m_mapView = findChild<MapQuickView*>("mapView");

  // Create a map using the topographic basemap
  m_map = new Map(BasemapStyle::ArcGISTopographic, this);

  // add a map image layer
  QUrl mapServiceUrl("https://sampleserver6.arcgisonline.com/arcgis/rest/services/SampleWorldCities/MapServer");
  ArcGISMapImageLayer* imageLayer = new ArcGISMapImageLayer(mapServiceUrl, this);
  m_map->operationalLayers()->append(imageLayer);

  // hide 2 of the sublayers in the map image layer
  connect(imageLayer, &ArcGISMapImageLayer::doneLoading, this, [imageLayer](Error e)
  {
    if (!e.isEmpty())
    {
      qDebug() << e.message() << e.additionalMessage();
      return;
    }

    imageLayer->mapImageSublayers()->at(1)->setVisible(false);
    imageLayer->mapImageSublayers()->at(2)->setVisible(false);
  });

  // add a feature layer
  QUrl featureLayerUrl("https://sampleserver6.arcgisonline.com/arcgis/rest/services/DamageAssessment/FeatureServer/0");
  ServiceFeatureTable* featureTable = new ServiceFeatureTable(featureLayerUrl, this);
  FeatureLayer* featureLayer = new FeatureLayer(featureTable, this);
  m_map->operationalLayers()->append(featureLayer);

  // set an initial viewpoint
  const double mapScale = 68015210;
  const double x = -10977012.785807;
  const double y = 4514257.550369;
  const Point pt(x, y, SpatialReference::webMercator());
  Viewpoint initialViewpoint(pt, mapScale);
  m_map->setInitialViewpoint(initialViewpoint);

  // Set map to map view
  m_mapView->setMap(m_map);

  // connect signals
  connectSignals();
}

void IdentifyLayers::connectSignals()
{
  // identify layers on mouse click
  connect(m_mapView, &MapQuickView::mouseClicked, this, [this](QMouseEvent& mouseEvent)
  {
    const double tolerance = 12.0;
    const bool returnPopups = false;
    const int maxResults = 10;
    m_mapView->identifyLayers(mouseEvent.x(), mouseEvent.y(), tolerance, returnPopups, maxResults);
  });

  // handle the identify results
  connect(m_mapView, &MapQuickView::identifyLayersCompleted, this, [this](QUuid, const QList<IdentifyLayerResult*>& results)
  {
    // reset the message text
    m_message = QString();
    int i = 0;

    for (IdentifyLayerResult* result : results)
    {
      ++i;
      // lambda for calculating result count
      auto geoElementsCountFromResult = [] (IdentifyLayerResult* result) -> int
      {
        // create temp list
        QList<IdentifyLayerResult*> tempResults{result};

        // use Depth First Search approach to handle recursion
        int count = 0;
        int index = 0;

        while (index < tempResults.length())
        {
          //get the result object from the array
          IdentifyLayerResult* identifyResult = tempResults[index];

          // update count with geoElements from the result
          count += identifyResult->geoElements().length();

          // check if the result has any sublayer results
          // if yes then add those result objects in the tempResults
          // array after the current result
          if (identifyResult->sublayerResults().length() > 0)
          {
            tempResults.append(identifyResult->sublayerResults().at(index));
          }

          // update the count and repeat
          index += 1;
        }
        return count;
      };

      const int count = geoElementsCountFromResult(result);
      QString layerName = result->layerContent()->name();
      m_message += QString("%1 : %2").arg(layerName).arg(count);
      // add new line character if not the final element inthe array
      if (i != results.length())
        m_message += "\n";
    }

    emit messageChanged();
    emit showMessage();
    qDeleteAll(results);
  });
}

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