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 On Demand▲

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

Service in Separate Process▲

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

<!-- 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 core-private

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.

For more information, see the Qt Android Notifier Example.

Android BroadcastReceiver enables exchanging messages between the Android system, apps, activities and services. Similarly to other Android features, Qt can use broadcast receivers to exchange messages between QtActivity and your service. Let's start with logic to send a message from your service. Add the following in your service implementation, which calls sendBroadcast():

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

    Intent sendToUiIntent = new Intent();
    sendToUiIntent.setAction(ActivityUtils.BROADCAST_CUSTOM_ACTION);
    sendToUiIntent.putExtra("message", "simple_string");

    Log.i(TAG, "Service sending broadcast");
    sendBroadcast(sendToUiIntent);

    return ret;
}

Then, you need to create and register the broadcast receiver from the Qt's main activity. The easiest way is to create a custom class with a method and implement all that logic in Java. In the following example, the service sends a message "simple_string" to Qt by calling the native method sendToQt():

public class ServiceBroadcastUtils {

    private static native void sendToQt(String message);

    private static final String TAG = "ActivityUtils";
    public static final String BROADCAST_CUSTOM_ACTION = "org.qtproject.example.qtandroidservice.broadcast.custom";

    public void registerServiceBroadcastReceiver(Context context) {
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(BROADCAST_CUSTOM_ACTION);
        context.registerReceiver(serviceMessageReceiver, intentFilter);
        Log.i(TAG, "Registered broadcast receiver");
    }

    private BroadcastReceiver serviceMessageReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            Log.i(TAG, "In OnReceive()");
            if (BROADCAST_CUSTOM_ACTION.equals(intent.getAction())) {
                String message = intent.getStringExtra("message");
                sendToQt(data);
                Log.i(TAG, "Service sent back message to C++: " + message);
            }
        }
    };
}

To make use of all that, start your service as shown in Start the Service, an then register the broadcast receiver by calling the method registerServiceBroadcastReceiver():

QJniEnvironment env;
jclass javaClass = env.findClass("org/qtproject/example/qtandroidservice/ActivityUtils");
QJniObject classObject(javaClass);

classObject.callMethod<void>("registerServiceBroadcastReceiver",
                             "(Landroid/content/Context;)V",
                             QtAndroid::androidContext().object());

Qt Remote Objects offers an easy way to share APIs between Qt processes. The main concept is to server in the service process, and have a replica in the Qt application, then those two parts are able to exchange data between each other, using signals and slots.

Prepare the replica▲

class ServiceMessenger {
    SLOT(void ping(const QString &message));
    SIGNAL(pong(const QString &message));
}

#include "rep_servicemessenger_source.h"

class ServiceMessenger : public ServiceMessengerSource {
public slots:
    void ping(const QString &name) override {
        emit pong("Hello " + name);
    }
};

QT += remoteobjects
REPC_REPLICA += servicemessenger.rep

QT += remoteobjects
REPC_SOURCE += servicemessenger.rep

Connect the source and replica▲

#include "servicemessenger.h"

#include <QDebug>
#include <QAndroidService>

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

    QRemoteObjectHost srcNode(QUrl(QStringLiteral("local:replica")));
    ServiceMessenger serviceMessenger;
    srcNode.enableRemoting(&serviceMessenger);

    return app.exec();
}

QRemoteObjectNode repNode;
repNode.connectToNode(QUrl(QStringLiteral("local:replica")));
QSharedPointer<ServiceMessengerReplica> rep(repNode.acquire<ServiceMessengerReplica>());
bool res = rep->waitForSource();
Q_ASSERT(res);

QObject::connect(rep.data(), &ServiceMessengerReplica::pong, [](const QString &message){
    qDebug() << "Service sent: " << message;
});
rep->ping("Qt and Android are friends!");

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.