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# QDesignerContainerExtension Class Reference
[QtDesigner module]

The QDesignerContainerExtension class allows you to add pages to a custom multi-page container in Qt Designer's workspace. More...

    #include <QDesignerContainerExtension>

- List of all members, including inherited members

### Public Functions

- virtual ~QDesignerContainerExtension ()
- virtual void addWidget ( QWidget * page ) = 0
- virtual int count () const = 0
- virtual int currentIndex () const = 0
- virtual void insertWidget ( int index, QWidget * page ) = 0
- virtual void remove ( int index ) = 0
- virtual void setCurrentIndex ( int index ) = 0
- virtual QWidget * widget ( int index ) const = 0

## Detailed Description

The QDesignerContainerExtension class allows you to add pages to a custom multi-page container in Qt Designer's workspace.

QDesignerContainerExtension provide an interface for creating custom container extensions. A container extension consists of a collection of functions that Qt Designer needs to manage a multi-page container plugin, and a list of the container's pages.

Warning: This is not an extension for container plugins in general, only custom multi-page containers.

To create a container extension, your extension class must inherit from both QObject and QDesignerContainerExtension. For example:

        class MyContainerExtension : public QObject,
               public QDesignerContainerExtension
        {
            Q_OBJECT
            Q_INTERFACES(QDesignerContainerExtension)

        public:
            MyContainerExtension(MyCustomWidget *widget,
                                 QObject *parent = 0);
            int count() const;
            QWidget *widget(int index) const;
            int currentIndex() const;
            void setCurrentIndex(int index);
            void addWidget(QWidget *widget);
            void insertWidget(int index, QWidget *widget);
            void remove(int index);

        private:
            MyCustomWidget *myWidget;
        };

Since we are implementing an interface, we must ensure that it's made known to the meta object system using the Q_INTERFACES() macro. This enables Qt Designer to use the qobject_cast() function to query for supported interfaces using nothing but a QObject pointer.

You must reimplement several functions to enable Qt Designer to manage a custom multi-page container widget: Qt Designer uses count() to keep track of the number pages in your container, widget() to return the page at a given index in the list of the container's pages, and currentIndex() to return the list index of the selected page. Qt Designer uses the addWidget() function to add a given page to the container, expecting it to be appended to the list of pages, while it expects the insertWidget() function to add a given page to the container by inserting it at a given index.

In Qt Designer the extensions are not created until they are required. For that reason you must also create a QExtensionFactory, i.e a class that is able to make an instance of your extension, and register it using Qt Designer's extension manager.

When a container extension is required, Qt Designer's extension manager will run through all its registered factories calling QExtensionFactory::createExtension() for each until the first one that is able to create a container extension, is found. This factory will then create the extension for the plugin.

There are four available types of extensions in Qt Designer: QDesignerContainerExtension , QDesignerMemberSheetExtension, QDesignerPropertySheetExtension and QDesignerTaskMenuExtension. Qt Designer's behavior is the same whether the requested extension is associated with a multi page container, a member sheet, a property sheet or a task menu.

The QExtensionFactory class provides a standard extension factory, and can also be used as an interface for custom extension factories. You can either create a new QExtensionFactory and reimplement the QExtensionFactory::createExtension() function. For example:

        QObject *ANewExtensionFactory::createExtension(QObject *object,
                const QString &iid, QObject *parent) const
        {
            if (iid != Q_TYPEID(QDesignerContainerExtension))
                return 0;

            if (MyCustomWidget *widget = qobject_cast<MyCustomWidget*>
                   (object))
                return new MyContainerExtension(widget, parent);

            return 0;
        }

Or you can use an existing factory, expanding the QExtensionFactory::createExtension() function to make the factory able to create a container extension as well. For example:

        QObject *AGeneralExtensionFactory::createExtension(QObject *object,
                const QString &iid, QObject *parent) const
        {
            MyCustomWidget *widget = qobject_cast<MyCustomWidget*>(object);

            if (widget && (iid == Q_TYPEID(QDesignerTaskMenuExtension))) {
                return new MyTaskMenuExtension(widget, parent);

            } else if (widget && (iid == Q_TYPEID(QDesignerContainerExtension))) {
                return new MyContainerExtension(widget, parent);

            } else {
                return 0;
            }
        }

For a complete example using the QDesignerContainerExtension class, see the Container Extension example. The example shows how to create a custom multi-page plugin for Qt Designer.

See also QExtensionFactory, QExtensionManager, and Creating Custom Widget Extensions.

## Member Function Documentation

### QDesignerContainerExtension::~QDesignerContainerExtension () `[virtual]`

Destroys the extension.

### void QDesignerContainerExtension::addWidget ( QWidget * page ) `[pure virtual]`

Adds the given page to the container by appending it to the extension's list of pages.

See also insertWidget(), remove(), and widget().

### int QDesignerContainerExtension::count () const `[pure virtual]`

Returns the number of pages in the container.

### int QDesignerContainerExtension::currentIndex () const `[pure virtual]`

Returns the index of the currently selected page in the container.

See also setCurrentIndex().

### void QDesignerContainerExtension::insertWidget ( int index, QWidget * page ) `[pure virtual]`

Adds the given page to the container by inserting it at the given index in the extension's list of pages.

See also addWidget(), remove(), and widget().

### void QDesignerContainerExtension::remove ( int index ) `[pure virtual]`

Removes the page at the given index from the extension's list of pages.

See also addWidget() and insertWidget().

### void QDesignerContainerExtension::setCurrentIndex ( int index ) `[pure virtual]`

Sets the the currently selected page in the container to be the page at the given index in the extension's list of pages.

See also currentIndex().

### QWidget * QDesignerContainerExtension::widget ( int index ) const `[pure virtual]`

Returns the page at the given index in the extension's list of pages.

See also addWidget() and insertWidget().