Using Play Feature Delivery

This document describes the functionality of the Feature Delivery example. The example uses features supported since Qt 6.11.
Play Feature Delivery can be used on older Qt versions, but creating the application requires manual addition of Android project and copying Qt binaries. Instructions for that are found in chapter Feature Delivery on pre Qt 6.11.

What is Feature Delivery?

Play Feature Delivery is a capability offered by Google which essentially allows developers to structure their projects in a way that the Google Play store can split their app content into several downloadable packages. It also gives developers control over how the content is delivered to users. These split software and content packages are delivered to the Google Play store using Android App Bundles (AAB). Google's developer documentation details this feature.

Example project: Feature Delivery Map Loader

This simple app uses Play Feature Delivery to serve images to a user when requested. The app can be easily modified to create an app that is over 200MB to test the app size limits and download using a large Feature Delivery module.

The App

The application consists of a draggable view and four buttons.

• On Startup Load Map and Show Map Info buttons are enabled.
• When clicked Show Map Info button just shows that there are no information available.
• Load Map initiates loading of the feature module:
  1. Download pop-up is shown, from the pop-up the download can be canceled.
  2. When download completes the pop-up is removed and
  3. Change Map and Remove Map buttons are enabled.
• Remove Map button requests feature module to be uninstalled, disabling enabled buttons.
• When Change Map is clicked it opens a view where a map shown can be changed. In this example feature module consists of only one winter-themed map image.

Source folder setup

• fdwintermapmodule: Feature Module
• fdmaploader: The main app
• fdmaploader/storeloader: Feature Delivery JNI interface

Feature Delivery interface

The fdmaploader/storeloader folder contains interface class PlayStoreLoader for the Feature Delivery API. The API is not complete, but contains relevant functions for loading and removing feature modules. Module loading is initiated with a call to PlayStoreLoader::loadModule. Status of the process can be monitored with signals provided by PlayStoreLoaderHandler. A handle to the callbacks can be obtained with PlayStoreLoader::getHandler function. The example API also provides a way to check already installed modules with PlayStoreLoader::getInstalledModules function and a option to remove installed modules with PlayStoreLoader::uninstallModules

This example is designed so that a developer can easily add their own content to test the Feature Delivery. To exceed the Play Store maximum package size, map images (It does not need to be map images, but it fits the theme of the example.) can be added to the images folders in fdmaploader and fdwintermapmodule, the image names must also be added to the images.qrc file.

Under the hood

The API module consists of two parts. Qt interface (PlayStoreLoader and PlayStoreLoaderHandler) and java classes that handle calling the Android: Google Split Install Interfaces. Qt interface works mostly as a passthrough for the java classes. Qt interface simplifies the API so, that when feature module is being loaded, Google SplitCompat and SplitInstall classes and listeners are created and released automatically. In this example parts of the APIs are left out, such as deferredInstall and language support.
Qt creates and builds package suitable for Google Play deployment using qt6_add_android_dynamic_features when it is defined CMakeLists.

qt6_add_android_dynamic_features(${target_name}
    FEATURE_TARGETS fdwintermapmodule)

CMake function qt6_add_android_dynamic_features adds the specific dynamic library as the dynamic feature for the Android application target. it requires QT_USE_ANDROID_MODERN_BUNDLE feature to be enabled. That can be done either as a compile-time flag or set in CMakeLists. The folder where the Java part of the interface resides is added to the build using qt_add_android_dynamic_feature_java_source_dir.

On the Example app modules are loaded using storeloader interface. Qt PlayStoreLoader functions and PlayStoreLoaderHandler class work as an intermediate between the example code and Java.

void PlayStoreLoader::loadModule(const QString & callId,
    const QString &moduleName)
{
    if (callId.isEmpty() || moduleName.isEmpty())
        return;
    if (!loaderInstance->registerNatives())
        return;
    if (!loaderInstance->loader().isValid()) {
        qCritical("StoreLoader not constructed");
        return;
    }
    loaderInstance->loader().callMethod<void>("installModuleFromStore", moduleName, callId);
}

Java classes handle calls to the Split Install API.

        m_splitInstallManager.startInstall(request)
                .addOnSuccessListener(sessionId -> {
                    PlayStoreLoaderListener listener = m_listeners.get(callId);
                    if (listener != null)
                        listener.setSessionId(sessionId);
                });

Creating Binaries

Using command line a locally testable AAB package can be built.

Create and enter a build directory to the same level with source directory:

mkdir build-feature-delivery/ ; cd build-feature-delivery/

Configure:

path-to-qt-version/path-to-abi/bin/qt-cmake -GNinja -B . -S ../feature-delivery/ -DQT_USE_TARGET_ANDROID_BUILD_DIR=ON -DCMAKE_BUILD_TYPE=Debug

Build:

ninja aab

Testing

The built AAB can be tested locally by using bundletool with --local-testing parameter. Android: Bundletool Documentation The bundletool build-apks command creates apks file which then can be installed on a device or emulator with install-apks command

Bundletool commands used

Generate APK:s from a bundle:

bundletool build-apks --bundle=/path/to/bundle.aab --output=/path/to/apk/package.apks --local-testing

Install app to the device:

bundletool install-apks --apks=/path/to/apk/package.apks

Delivering to Play Store

In order to be able to upload the created AAB package to the Google Play Store the package must be signed. For that jarsigner can be used. Below is an example jarsigner command to sign the AAB package. See Android: Jarsigner Documentation

jarsigner -verbose -sigalg SHA256withRSA -digestalg SHA-256 -keystore [path-to-keystore-file].keystore [path-to-aab-file].aab [alias]

Feature Delivery on pre Qt 6.11

Versions prior Qt 6.11 does not support Google Play Store compatible package generation. If you are not able to use a Qt version 6.11 or later there is a way to use Google Play Feature Delivery, but it requires manual creation of the Android project, and copying of the Qt binaries to it. Rest of the document have instructions how to achieve that. The instructions may not be 1-to-1 compatible for all environments, but should give good hints to achieve successful Feature Delivery implementation. It is advised to use the example as a basis.

Feature Module

Feature modules are build like normal libraries.

• Use Qt Creator to create a C++ shared library.
• Implement features and add resources.
• Build to create .so binaries.

Feature Delivery handles C++ libraries like normal shared libraries that may or may not be available at runtime. Before calls to a library, the availability of one must be checked.

Main App (Qt)

• Use Qt Creator to create an app (Qt Quick project template was used here).
• Implement access to the Feature Delivery library. The central class in Google Play Feature Delivery Java library is Android: SplitInstallManager.
• Android template files can be created by using the 'Create Templates' button on QtCreator Projects -> Build&Run -> [target ABI] -> Build Steps -> Build Android APK. Templates are created in the 'android' folder in the project.
• Add Java files to the folder .../android/src/java/[package...] and file paths to CMakeLists.txt:

  qt_add_executable...
  ...[path]/[java-filename.java]
  ...

• In the example, a Java class was created to handle the calls and callbacks. The Java class would then be accessed from Qt using JNI. Android: Request an on demand module section in the Android documentation has a simple description of how to request a module.
• When adding Java files under the android folder in the project, QT_ANDROID_PACKAGE_SOURCE_DIR property must be added to the CMakeLists.txt:

  ...
  set_property(TARGET appFDMainApp APPEND PROPERTY QT_ANDROID_PACKAGE_SOURCE_DIR
               ${CMAKE_CURRENT_SOURCE_DIR}/android)
  ...

• Also, the main app build.gradle must have dependencies for the feature API: in the dependencies block, replace

  implementation 'androidx.core:core:1.13.1'

  with

  implementation("com.google.android.play:feature-delivery:2.1.0")

• Implement access to the library provided by the feature module. As the Feature Module may or may not be available to the main app, modules are not linked at build time and calls to the module must be resolved at runtime. Example:

  QString MapLoader::loadMapInfo()
  {
      QScopedPointer<QString> resultStr;
      typedef void* (*LoadMapInfoFunc)();
      //Find if wintermap library exists
      mWintermapLibrary.setFileName("fdwintermapmodule");
      if (!mWintermapLibrary.load()) {
          qWarning() << Q_FUNC_INFO << "Failed to load library";
          return QString();
      }
      LoadMapInfoFunc loadMapInfo = (LoadMapInfoFunc) mWintermapLibrary.resolve("loadMapInfo");
      if (loadMapInfo) {
          void* result = loadMapInfo();
          resultStr.reset(static_cast<QString*>(result));
      } else
          qWarning() << Q_FUNC_INFO << "Function loadMapInfo not loaded";
  
      return *resultStr.data();
  }

• Implement the user interface and other required parts of the main app.

Feature Module (Qt)

• Use Qt Creator to create an app (Qt C++ Library project template was used).
• Implement features the module offers.

Android Project (Android)

Creating a project for building an Android app bundle for Feature Delivery is based on Android's documentation, mainly:

• Android: Android Feature Delivery Documentation

Create an Android project manually or using Android Studio (Using the 'No Activity' template). The project is modified so that it contains a top-level project and two sub-projects, app and feature-module. The Android Studio template creates the app sub-project and the feature-module can be added using File -> New -> New Module template.

The template project requires several modifications:

• Add Feature Delivery plugin to the main level build.gradle:

  plugins {
      id 'com.android.application' version '8.5.2' apply false
      id 'com.android.dynamic-feature' version '8.5.2' apply false
      id 'com.android.library' version '8.5.2' apply false
  }

• Add feature module to the settings.gradle, change rootProject.name if needed:

  ...
  rootProject.name = "name-of-the-root-project"
  include(:app)
  include(:name-of-the-feature-module)

app - Sub-project

• Android project requires Qt binaries from the Main App project:
  • Copy native libraries in Qt build: [build directory]/android-build/libs/[target ABI] to app/src/main/jniLibs/[target ABI]
  • Copy jars in [build directory]/android-build/libs/ to app/libs/
• From the Qt build, also contents of the res folder, AndroidManifest.xml, and local.properties are copied to respective places in the Android project.
• Add file feature_names.xml to the app/src/main/res/values folder containing a string for the feature module:

  <?xml version="1.0" encoding="utf-8"?>
  <resources>
      <string name="feature_module_name">name-of-the-feature-module-here</string>
  </resources>

• Add file keep.xml to app/src/main/res/raw folder containing:

  <?xml version="1.0" encoding="utf-8"?>
  <resources xmlns:tools="http://schemas.android.com/tools"
      tools:keep="@string/feature_module_winter_map"
      tools:discard="" />

Modifications to app sub-project build files

Build files copied to the Android project need some modifications.

app - Sub-project

• Remove buildScript and repositories blocks.
• Android block in main app's build.gradle requires some modifications:
  • defaultConfig
  • packagingOptions
  • dynamicFeatures
  • sourceSets
  • aaptOptions
  • dependencies

android {
...
  defaultConfig {
  ...
    applicationId "your-project-name-here"
  ...
  }
  packagingOptions.jniLibs.useLegacyPackaging true

  dynamicFeatures = [":your-dynamic-feature-name-here"]

  sourceSets {
    main {
      manifest.srcFile 'src/main/AndroidManifest.xml'
      java.srcDirs = [qtAndroidDir + '/src', 'src', 'java']
      aidl.srcDirs = [qtAndroidDir + '/src', 'src', 'aidl']
      res.srcDirs = [qtAndroidDir + '/res', 'res']
      resources.srcDirs = ['resources']
      renderscript.srcDirs = ['src']
      assets.srcDirs = ['assets']
      jniLibs.srcDirs = ['src/main/jniLibs/']
    }
  }

  // Do not compress Qt binary resources file
  aaptOptions {
    noCompress 'rcc'
  }
...
}

dependencies {
...
  implementation fileTree(dir: 'libs', include: ['*.jar', '*.aar'])
  implementation 'com.google.android.play:feature-delivery:2.1.0'
  implementation libs.material
...
}

Also add signing configuration to android block:

android {
...
  signingConfigs {
    release {
      storeFile file("/absolute/path/to/the/keystore.jks")
      storePassword "myStorePassword"
      keyAlias "myKeyAlias"
      keyPassword "myKeyPassword"
    }
  }
  buildTypes {
    release {
      signingConfig signingConfigs.release
      ...
    }
  }
...
}

Qt has added project variables to gradle.properties. Change the value of androidPackageName if needed.

• Remove package:

  ...
  <manifest
  ...
    android:package... <--remove
  ...
  >
  ...

• Change label and android.app.lib_name if needed:

  ...
  <application ...
    android:label=" ...
    <activity ... >
      <meta-data android:name="android.app.lib_name" android:value=" ...
      />
  ...

feature-module - Sub-project

App and feature modules are created as sub-projects for the top-level Android project. The folder and file structure is similar to the app sub-project.

• Feature-module binaries from the Qt build are copied to the [name-of-feature-module]/src/main/jniLibs/
• Like in the main app, src/main/res/ folder should have xml and values folders containing qtprovider_paths.xml and libs.xml respectively. Both files can be copied from the app project.
• If src/main/res/ folder contains drawable or mipmap folders and the feature does not require them, they can be removed.
• In the feature module src/main/res/values should not contain app_name field. In simple projects where strings.xml is not needed for other uses, it can be removed.
• libs.xml contains only the name of the feature module:

  ...
      <array name="load_local_libs">
          <item>name-of-the-feature-module-here</item>
      </array>
  
      <string name="static_init_classes"></string>
      <string name="use_local_qt_libs">0</string>
      <string name="bundle_local_qt_libs">0</string>
  ...

• AndroidManifest.xml is added to the src/main/ directory:

  <?xml version="1.0" encoding="utf-8"?>
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:dist="http://schemas.android.com/apk/distribution">
  
      <dist:module
          dist:instant="false"
          dist:title="@string/feature_module_title_string">
          <dist:delivery>
              <dist:on-demand />
          </dist:delivery>
          <dist:fusing dist:include="false" />
      </dist:module>
      <!-- This feature module does contain code. -->
      <application android:hasCode="true"/>
  </manifest>

• Feature module build.gradle is quite similar to the one from the app project, with some changes. Here's an example:

  plugins {
      id 'com.android.dynamic-feature'
  }
  
  dependencies {
      implementation project(':app')
      implementation fileTree(dir: 'libs', include: ['*.jar', '*.aar'])
      implementation 'com.google.android.play:feature-delivery:2.1.0'
  }
  
  android {
  
      namespace = androidPackageName
      compileSdk = androidCompileSdkVersion
      ndkVersion androidNdkVersion
  
      // Extract native libraries from the APK
      packagingOptions.jniLibs.useLegacyPackaging true
  
      defaultConfig {
          resConfig "en"
          minSdkVersion qtMinSdkVersion
          targetSdkVersion qtTargetSdkVersion
      }
  
      sourceSets {
          main {
              manifest.srcFile 'src/main/AndroidManifest.xml'
              resources.srcDirs = ['resources']
              renderscript.srcDirs = ['src']
              assets.srcDirs = ['assets']
              jniLibs.srcDirs = ['src/main/jniLibs/']
         }
      }
  
      tasks.withType(JavaCompile) {
          options.incremental = true
      }
  
      compileOptions {
          sourceCompatibility JavaVersion.VERSION_1_8
          targetCompatibility JavaVersion.VERSION_1_8
      }
  
      lintOptions {
          abortOnError false
      }
  
      // Do not compress Qt binary resources file
      aaptOptions {
          noCompress 'rcc'
      }
  }

• gradle.properties file can be copied over from the app sub-project, change the androidPackageName to the feature module package.

Building and deployment

AAB bundle can be built from the command line using gradle wrapper: ./gradlew bundle The produced AAB will be in build/outputs/bundle/release (or debug) folder. The AAB can then be copied to the Google Play Store and released for testing. Testing can also be done locally by using bundletool with --local-testing parameter.

Example project @ code.qt.io