Add layers to a map (offline)

Overview

You will learn: how to build an app that loads a basemap and feature layers from a mobile map package file.

Offline maps allow users to load basemaps and layers when their network connectivity is poor or offline. Mobile map packages (.mmpk files) can be created in ArcGIS Pro and loaded in your app with the MobileMapPackage class.

In this tutorial you will learn how to load a mobile map package and then use it in your app.

Before you begin

You must have previously installed the ArcGIS Runtime SDK for Qt and set up the development environment for your operating system.

Open the starter app project

If you have already completed the Create a starter app tutorial, start Qt Creator and open your starter app project. Otherwise, download and unzip the starter app project solution, and then open it in Qt Creator.

Prepare your data

You will need an .mmpk file to complete this tutorial. You can how to create mobile map packages in the Prepare your data for offline use. Alternatively, download the map package we prepared, and save the file somewhere on your development machine.

Steps

Save the path of the mobile map package

1. You will need the absolute path of the mobile map package file. The path /your_local_path/offline-maps-package.mmpk is a placeholder in the code below. Change this to match your file system.

Import headers and declare member variables

1. In Projects, double click on Headers > Create_a_starter_app.h, add MobileMapPackage to the namespace along with two additional include statements.

   class MapQuickView;
   
   // *** ADD ***
   class MobileMapPackage;
   }
   
   }
   
   #include <QObject>
   
   // *** ADD ***
   #include <QTemporaryDir>
   #include <QString>
   

2. Add the public member functions openMapPackage and createMapPackage.

   public:
     explicit Create_a_starter_app(QObject* parent = nullptr);
     ~Create_a_starter_app() override;
   
     // *** ADD ***
     void openMapPackage(const QString& dataPath);
     void createMapPackage(const QString& dataPath);
   

3. Add the private member variables m_mmpk and m_unpackTempDir.

     Esri::ArcGISRuntime::MapQuickView* m_mapView = nullptr;
   
     // *** ADD ***
     Esri::ArcGISRuntime::MobileMapPackage* m_mmpk = nullptr;
     QTemporaryDir m_unpackTempDir;
   

Load the mobile map package

1. In Projects, double click on Sources > Create_a_starter_app.cpp. Comment out #include"Basemap.h" because we don't need that class.

   // *** UPDATE ***
   // #include "Basemap.h"
   #include "Map.h"
   

2. We're displaying an offline map package, and Basemap is an online service. Accordingly, update the constructor to remove m_map from the initializer list in the constructor. Also remove the center and viewpoint objects and replace the body of the constructor with following code creating the map package.

   Create_a_starter_app::Create_a_starter_app(QObject* parent /* = nullptr */):
      // *** UPDATE ***
      // QObject(parent),
      // m_map(new Map(Basemap::topographicVector(this), this))
      QObject(parent)
   {
     // *** UPDATE ***
     // const Point center(-118.71511, 34.09042, SpatialReference::wgs84());
     // const Viewpoint viewpoint(center, 300000.0);
     // set the path below to your local path to this file
     const QString mmpk_path("/your_local_path/offline-maps-package.mmpk");
     createMapPackage(mmpk_path);
   }
   

3. Add the public member function createMapPackage to create a new MobileMapPackage and wait until it loads to add it to the map view.

   void Create_a_starter_app::createMapPackage(const QString& dataPath)
   {
     m_mmpk = new MobileMapPackage(dataPath, this);
   
     connect(m_mmpk, &MobileMapPackage::doneLoading, this, [this](Error e)
       {
         if (!e.isEmpty())
           {
             qDebug() << QString("Error loading package: %1 %2").arg(e.message(), e.additionalMessage());
             return;
           }
   
           if (!m_mmpk || !m_mapView || m_mmpk->maps().isEmpty())
           {
             return;
           }
   
           m_mapView->setMap(m_mmpk->maps().at(0));
      });
   
      m_mmpk->load();
   }
   

4. Run your code to load the offline map.

Congratulations, you're done!

Your map, as it was designed in ArcGIS Pro, should load and display with the view point centered on the Santa Monica Mountains. Compare your map with our completed solution project.

Challenge

Change map contents

Change map package