Service Browser Example

ServiceBrowser Class Implementation

 ServiceBrowser::ServiceBrowser(QWidget *parent, Qt::WindowFlags flags)
     : QWidget(parent, flags)
 {
     serviceManager = new QServiceManager(this);
     systemManager = new QServiceManager(QService::SystemScope);

     registerExampleServices();

     initWidgets();
     reloadServicesList();

     setWindowTitle(tr("Services Browser"));
 }

The constructor registers the "FileManagerService", "BluetoothTransferService" and "NotesManagerServices" services that are provided by the filemanagerplugin and bluetoothtransferplugin projects in the examples/ directory. It also calls reloadServicesList() to show these two newly registered services in the top-left pane.

 void ServiceBrowser::reloadServicesList()
 {
     servicesListWidget->clear();

     QSet<QString> services;
     QList<QServiceInterfaceDescriptor> descriptors = serviceManager->findInterfaces();
     for (int i=0; i<descriptors.count(); i++) {
         QString service = descriptors[i].serviceName();

         if (descriptors[i].scope() == QService::SystemScope)
             service += tr(" (system)");

         services << service;
     }

When the services list in the top-left pane needs to be refreshed, we call QServiceManager::findServices() to get a QStringList of all services that are currently registered with the service framework.

 void ServiceBrowser::reloadInterfaceImplementationsList()
 {
     ...
     ...
     QList<QServiceInterfaceDescriptor> descriptors = manager->findInterfaces(serviceName);

     attributesListWidget->clear();
     interfacesListWidget->clear();
     for (int i=0; i<descriptors.count(); i++) {
         if (descriptors[i].scope() != manager->scope() && !serviceName.isEmpty())
             continue;

         QString text = QString("%1 %2.%3")
                 .arg(descriptors[i].interfaceName())
                 .arg(descriptors[i].majorVersion())
                 .arg(descriptors[i].minorVersion());

         QServiceInterfaceDescriptor defaultInterfaceImpl
             = manager->interfaceDefault(descriptors[i].interfaceName());

         if (serviceName.isEmpty()) {
             text += " (" + descriptors[i].serviceName() + ")";

             if (descriptors[i].scope() == QService::SystemScope) {
                 text += tr(" (system");
                 defaultInterfaceImpl = systemManager->interfaceDefault(descriptors[i].interfaceName());
                 if (descriptors[i] == defaultInterfaceImpl)
                     text += tr(" default)");
                 else
                     text += ")";
                 defaultInterfaceImpl = QServiceInterfaceDescriptor();
             }
     ...
         }

To create the list of interface implementations in the bottom-left pane, we call QServiceManager::findInterfaces() to get a list of QServiceInterfaceDescriptor objects. If a particular service has been selected in the top-left pane, we call QServiceManager::findInterfaces() with the name of that service as the argument, so that it will only return the interface implementations provided by that service. Otherwise, it is called with no argument to retrieve a list of all implementations provided by all registered services.

The example maps each entry in the interface implementations list to its corresponding QServiceInterfaceDescriptor object using the QListWidgetItem::setData() method.

Note how we also call QServiceManager::defaultServiceInterface() to determine whether an interface implementation is the default for that interface.

 void ServiceBrowser::reloadAttributesList()
 {
     QListWidgetItem *item = interfacesListWidget->currentItem();
     if (!item)
         return;

     QServiceInterfaceDescriptor selectedImpl =
             item->data(Qt::UserRole).value<QServiceInterfaceDescriptor>();

     QObject *implementationRef;
     if (selectedImplRadioButton->isChecked())
         implementationRef = serviceManager->loadInterface(selectedImpl, 0, 0);
     else
         implementationRef = serviceManager->loadInterface(selectedImpl.interfaceName(), 0, 0);

     ...

The reloadAttributesList() method creates the list in the right-hand pane that shows the attributes of an interface implementation that can be invoked through the Qt meta-object system.

QServiceManager::loadInterface() is called to get an instance of the identified interface implementation. This method finds the corresponding service plugin and returns the QObject instance provided by the service plugin's QServicePluginInterface::createInstance() method.

     ...
     const QMetaObject *metaObject = implementationRef->metaObject();
     attributesGroup->setTitle(tr("Invokable attributes for %1 class")
             .arg(QString(metaObject->className())));
     for (int i=0; i<metaObject->methodCount(); i++) {
         QMetaMethod method = metaObject->method(i);
         attributesListWidget->addItem("[METHOD] " + QString(method.signature()));
     }
     for (int i=0; i<metaObject->propertyCount(); i++) {
         QMetaProperty property = metaObject->property(i);
         attributesListWidget->addItem("[PROPERTY] " + QString(property.name()));
     }
 }

Call QObject::metaObject() on the implementation instance to get a QMetaObject instance that reveals the dynamically invokable attributes for the instance. These attributes include properties, signals, slots, and methods marked with the Q_INVOKABLE macro. Call QMetaObject::method() to get information about a signal, slot or invokable method, and QMetaObject::property() to access a property of the instance.

When you know the name of the method you wish to invoke, call QMetaObject::invoke() or QMetaMethod::invoke() to invoke it dynamically. Similarly, QMetaProperty::read() and QMetaProperty::write() can be used to read and modify the value of a property.

 class FileManagerStorage : public QObject
 {
     Q_OBJECT
     Q_PROPERTY(QString workingDirectory READ workingDirectory WRITE setWorkingDirectory)

 public:
     FileManagerStorage(QObject *parent = 0);

     void setWorkingDirectory(const QString &path);
     QString workingDirectory() const;

 signals:
     void workingDirectoryChanged(const QString &newDir);

 public slots:
     void copyFile(const QString &currentPath, const QString &newPath);

 private:
     QString directory;
 };

 QObject *interfaceImpl = QServiceManager::loadInterface("com.nokia.qt.examples.FileStorage", 0, 0);
 QMetaObject::invokeMethod(interfaceImpl, "copyFile",
                           Q_ARG(QString, "path/to/file.txt"),
                           Q_ARG(QString, "new/path/to/file.txt"));