COM App Example (ActiveQt) | Active Qt 5.6

Qt 5.6 | Active Qt | COM App Example (ActiveQt)

Qt 5.6.2 Reference Documentation

# COM App Example (ActiveQt)

      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 identifier. 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) - this allows COM clients to connect to an already instantiated COM object.

      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 qobject_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 qobject_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 straightforward.

      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->setVisible(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 quit() through a single-shot-timer, which is necessary to 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 throughout the `Application` API.

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

          // 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(&app, &QGuiApplication::lastWindowClosed, &appobject, &Application::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.

Application exiting is controlled explicitly - if COM started the application, then the client code has to call quit(); if the user started the application, then the application terminates when the last window has been closed.

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, start a new "Standard Exe" project and add a project reference to the comappLib type library. Create a form with a listbox "DocumentList", a static label "DocumentsCount" and a command button "NewDocument". Finally, implement the code for 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\activeqt\comapp`.

Files:

- activeqt/comapp/main.cpp
- activeqt/comapp/comapp.pro