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# Supporting COM in a Qt Application

This examples shows how to use ActiveQt to develop a Qt application that can be automated via COM. Different QObject based classes are exposed as COM object that communicate with the GUI of the running Qt application. The APIs of those COM objects has been designed to resemble the APIs of standard COM applications, i.e. those from Microsoft Office.

        class Application : public QObject
        {
            Q_OBJECT

            Q_CLASSINFO("ClassID", "{b50a71db-c4a7-4551-8d14-49983566afee}")
            Q_CLASSINFO("InterfaceID", "{4a427759-16ef-4ed8-be79-59ffe5789042}")
            Q_CLASSINFO("RegisterObject", "yes")

            Q_PROPERTY(DocumentList* documents READ documents)
            Q_PROPERTY(QString id READ id)
            Q_PROPERTY(bool visible READ isVisible WRITE setVisible)

        public:
            Application(QObject *parent = 0);
            DocumentList *documents() const;

            QString id() const { return objectName(); }

            void setVisible(bool on);
            bool isVisible() const;

            QTabWidget *window() const { return ui; }

        public slots:
            void quit();

        private:
            DocumentList *docs;

            QTabWidget *ui;
        };

The first class `Application` represents the application object. It exposes read-only properties `documents` and `id` to get access to the list of documents, and an identifiers. A read/write property `visible` controls whether the QTabWidget-based user interface of the application should be visible, and a slot `quit()` terminates the application.

The RegisterObject attribute is set to make sure that instances of this class are registered in COM's running object table (ROT).

        class DocumentList : public QObject
        {
            Q_OBJECT

            Q_CLASSINFO("ClassID", "{496b761d-924b-4554-a18a-8f3704d2a9a6}")
            Q_CLASSINFO("InterfaceID", "{6c9e30e8-3ff6-4e6a-9edc-d219d074a148}")

            Q_PROPERTY(Application* application READ application)
            Q_PROPERTY(int count READ count)

        public:
            DocumentList(Application *application);

            int count() const;
            Application *application() const;

        public slots:
            Document *addDocument();
            Document *item(int index) const;

        private:
            QList<Document*> list;
        };

The `DocumentList` class stores a list of documents. It provides an API to read the number of documents, to access each document by index and to create a new document. The `application` property returns the root object.

        class Document : public QObject
        {
            Q_OBJECT

            Q_CLASSINFO("ClassID", "{2b5775cd-72c2-43da-bc3b-b0e8d1e1c4f7}")
            Q_CLASSINFO("InterfaceID", "{2ce1761e-07a3-415c-bd11-0eab2c7283de}")

            Q_PROPERTY(Application *application READ application)
            Q_PROPERTY(QString title READ title WRITE setTitle)

        public:
            Document(DocumentList *list);
            ~Document();

            Application *application() const;

            QString title() const;
            void setTitle(const QString &title);

        private:
            QWidget *page;
        };

The `Document` class finally represents a document in the application. Each document is represented by a page in the application's tab widget, and has a title that is readable and writable through the document's API. The `application` property again returns the root object.

        Document::Document(DocumentList *list)
        : QObject(list)
        {
            QTabWidget *tabs = list->application()->window();
            page = new QWidget(tabs);
            page->setWindowTitle("Unnamed");
            tabs->addTab(page, page->windowTitle());

            page->show();
        }

        Document::~Document()
        {
            delete page;
        }

        Application *Document::application() const
        {
            return qt_cast<DocumentList*>(parent())->application();
        }

        QString Document::title() const
        {
            return page->windowTitle();
        }

        void Document::setTitle(const QString &t)
        {
            page->setWindowTitle(t);

            QTabWidget *tabs = application()->window();
            int index = tabs->indexOf(page);
            tabs->setTabText(index, page->windowTitle());
        }

The implementation of the `Document` class creates a new page for the tab widget, and uses the title of that page for the title property. The page is deleted when the document is deleted.

        DocumentList::DocumentList(Application *application)
        : QObject(application)
        {
        }

        Application *DocumentList::application() const
        {
            return qt_cast<Application*>(parent());
        }

        int DocumentList::count() const
        {
            return list.count();
        }

        Document *DocumentList::item(int index) const
        {
            if (index >= list.count())
                return 0;

            return list.at(index);
        }

        Document *DocumentList::addDocument()
        {
            Document *document = new Document(this);
            list.append(document);

            return document;
        }

The `DocumentList` implementation is straight forward.

        Application::Application(QObject *parent)
        : QObject(parent), ui(0)
        {
            ui = new QTabWidget;

            setObjectName("From QAxFactory");
            docs = new DocumentList(this);
        }

        DocumentList *Application::documents() const
        {
            return docs;
        }

        void Application::setVisible(bool on)
        {
            ui->setShown(on);
        }

        bool Application::isVisible() const
        {
            return ui->isVisible();
        }

        void Application::quit()
        {
            delete docs;
            docs = 0;

            delete ui;
            ui = 0;
            QTimer::singleShot(0, qApp, SLOT(quit()));
        }

        #include "main.moc"

The `Application` class initializes the user interface in the constructor, and shows and hides it in the implementation of `setVisible()`. The object name (accessible through the `id` property) is set to `"From` QAxFactory" to indicate that this COM object has been created by COM. Note that there is no destructor that would delete the QTabWidget - this is instead done in the `quit()` slot, before calling QApplication::quit() through a single-shot-timer, which is necessary ensure that the COM call to the slot is complete.

        QAXFACTORY_BEGIN("{edd3e836-f537-4c6f-be7d-6014c155cc7a}", "{b7da3de8-83bb-4bbe-9ab7-99a05819e201}")
           QAXCLASS(Application)
           QAXTYPE(Document)
           QAXTYPE(DocumentList)
        QAXFACTORY_END()

The classes are exported from the server using the QAxFactory macros. Only `Application` objects can be instantiated from outside - the other APIs can only be used after accessing the respective objects throught the `Application` API.

        int main(int argc, char **argv)
        {
            QApplication app(argc, argv);

            // started by COM - don't do anything
            if (QAxFactory::isServer())
                return app.exec();

            // started by user
            Application appobject(0);
            appobject.setObjectName("From Application");

            QAxFactory::startServer();
            QAxFactory::registerActiveObject(&appobject);

            appobject.setVisible(true);
            QObject::connect(qApp, SIGNAL(lastWindowClosed()), &appobject, SLOT(quit()));

            return app.exec();
        }

The main() entry point function creates a QApplication, and just enters the event loop if the application has been started by COM. If the application has been started by the user, then the `Application` object is created and the object name is set to "From Application". Then the COM server is started, and the application object is registered with COM. It is now accessible to COM clients through the client-specific APIs.

Finally, the user interface is made visible, and the event loop is started.

A simple Visual Basic application could now access this Qt application. In VB, create a form with a listbox "DocumentList", a static label "DocumentsCount" and a command button "NewDocument". Then implement the code of the form like this:

        Private Application As comappLib.Application
        Private MyApp As Boolean

        Private Sub UpdateList()
            DocumentList.Clear
            DocumentsCount.Caption = Application.documents.Count
            For Index = 0 To Application.documents.Count - 1
               DocumentList.AddItem (Application.documents.Item(Index).Title)
            Next
        End Sub

        Private Sub Form_Load()
            On Error GoTo CreateNew
            Set Application = GetObject(, "comapp.Application")
            MyApp = False
            GoTo Initialized
        CreateNew:
            On Error GoTo InitializeFailed
            Set Application = New Application
            Application.Visible = True
            MyApp = True
        Initialized:
            Caption = Application.id
            UpdateList
        InitializeFailed:
        End Sub

        Private Sub Form_Unload(Cancel As Integer)
            If MyApp Then
                Application.quit
            End If
        End Sub

        Private Sub NewDocument_Click()
            Application.documents.addDocument
            UpdateList
        End Sub

To build the example you must first build the QAxServer library. Then run qmake and your make tool in `examples/comapp`.