Android Services

You can create a service by extending the class QtService or Android: Service to your Java class. Depending on whether you want to use Qt features in your service or call native C++ functions from Java, you need to extend either QtService or Service. Let's start with a simple service, as follows:

import android.content.Context;
import android.content.Intent;
import android.util.Log;
import org.qtproject.qt.android.bindings.QtService;

public class QtAndroidService extends QtService
{
    private static final String TAG = "QtAndroidService";

    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "Creating Service");
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "Destroying Service");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        int ret = super.onStartCommand(intent, flags, startId);

        // Do some work

        return ret;
    }
}

Android allows starting services on demand or at boot time. You can do both using Qt as well.

Start a Service At Boot Time▲

public class QtBootServiceBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Intent startServiceIntent = new Intent(context, QtAndroidService.class);
        context.startService(startServiceIntent);
    }
}

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

<receiver android:name=".QtBootServiceBroadcastReceiver">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED" />
    </intent-filter>
</receiver>

For the service to be usable in an Android app, you must declare it in the AndroidManifest.xml file. Let's start with adding the service section:

• When extending Service, just declare the service section as a normal Android service. Add the following inside the <application> section:

   

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  <service android:name=".QtAndroidService">
      <!-- Background running -->
      <meta-data android:name="android.app.background_running" android:value="true"/>
      <!-- Background running -->
  </service>

  This way the service will start in the same process as QtActivity, which allows you to use native C++ calls from Java code. You can run it in a separate process but that way you cannot use any native calls for communication because the Qt libraries are not loaded for that process. To run on separate process, add this to the service tag:

   

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  android:process=":qt_service"

   

• When extending QtService, you need to declare other items for loading all the necessary libs required for Qt, mainly the same items as in <activity> section for QtActivity. Add the following:

   

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  <service android:process=":qt_service" android:name=".QtAndroidService">
  
      <meta-data android:name="android.app.lib_name" android:value="service"/>
      <meta-data android:name="android.app.qt_sources_resource_id" android:resource="@array/qt_sources"/>
      <meta-data android:name="android.app.repository" android:value="default"/>
      <meta-data android:name="android.app.qt_libs_resource_id" android:resource="@array/qt_libs"/>
      <meta-data android:name="android.app.bundled_libs_resource_id" android:resource="@array/bundled_libs"/>
  
      <!-- Deploy Qt libs as part of package -->
      <meta-data android:name="android.app.bundle_local_qt_libs" android:value="-- %%BUNDLE_LOCAL_QT_LIBS%% --"/>
  
      <!-- Run with local libs -->
      <meta-data android:name="android.app.use_local_qt_libs" android:value="-- %%USE_LOCAL_QT_LIBS%% --"/>
      <meta-data android:name="android.app.libs_prefix" android:value="/data/local/tmp/qt/"/>
      <meta-data android:name="android.app.load_local_libs_resource_id" android:resource="@array/load_local_libs"/>
      <meta-data android:name="android.app.load_local_jars" android:value="-- %%INSERT_LOCAL_JARS%% --"/>
      <meta-data android:name="android.app.static_init_classes" android:value="-- %%INSERT_INIT_CLASSES%% --"/>
      <!-- Run with local libs -->
  
      <!-- Background running -->
      <meta-data android:name="android.app.background_running" android:value="true"/>
      <!-- Background running -->
  </service>

<meta-data android:name="android.app.background_running" android:value="true"/>

There are a few variations on how to declare services. Some of them are already used in the previous manifest snippet. Depending on your use case, run the service either in the same process as QtActivity or in a separate process.

Service in the Same Process as QtActivity▲

<service android:name=".QtAndroidService">

Service in Separate Process▲

<service android:process=":qt_service" android:name=".QtAndroidService">

<!-- Application arguments -->
<meta-data android:name="android.app.arguments" android:value="-service"/>
<!-- Application arguments -->

<meta-data android:name="android.app.lib_name" android:value="-- %%INSERT_APP_LIB_NAME%% --"/>

if (argc <= 1) {
    // code to handle main activity execution
} else if (argc > 1 && strcmp(argv[1], "-service") == 0) {
    qDebug() << "Service starting with from the same .so file";
    QAndroidService app(argc, argv);
    return app.exec();
} else {
    qWarning() << "Unrecognized command line argument";
    return -1;
}

TEMPLATE = lib
TARGET = service
CONFIG += dll
QT += core androidextras

SOURCES += \
    service_main.cpp

HEADERS += servicemessenger.h

#include <QDebug>
#include <QAndroidService>

int main(int argc, char *argv[])
{
    qWarning() << "Service starting from a separate .so file";
    QAndroidService app(argc, argv);

    return app.exec();
}

<meta-data android:name="android.app.lib_name" android:value="service"/>

This can work with services running in the same process as QtActivity and even if Service is extended.

QAndroidBinder is a convenience class that enables inter-process communication by implementing the most important methods in Android: Binder. It allows sending QByteArray or QVariant objects between processes.