Detailed Description

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.