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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...

Inherited by QPyDesignerContainerExtension.

### Methods

- __init__ (self)
- __init__ (self, QDesignerContainerExtension)
- addWidget (self, QWidget)
- int count (self)
- int currentIndex (self)
- insertWidget (self, int, QWidget)
- remove (self, int)
- setCurrentIndex (self, int)
- QWidget widget (self, int)

## 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.

## Method Documentation

### QDesignerContainerExtension.__init__ (self)

### QDesignerContainerExtension.__init__ (self, QDesignerContainerExtension)

### QDesignerContainerExtension.addWidget (self, QWidget)

This method is abstract and should be reimplemented in any sub-class.

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 (self)

This method is abstract and should be reimplemented in any sub-class.

Returns the number of pages in the container.

### int QDesignerContainerExtension.currentIndex (self)

This method is abstract and should be reimplemented in any sub-class.

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

See also setCurrentIndex().

### QDesignerContainerExtension.insertWidget (self, int, QWidget)

This method is abstract and should be reimplemented in any sub-class.

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().

### QDesignerContainerExtension.remove (self, int)

This method is abstract and should be reimplemented in any sub-class.

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

See also addWidget() and insertWidget().

### QDesignerContainerExtension.setCurrentIndex (self, int)

This method is abstract and should be reimplemented in any sub-class.

Sets 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 (self, int)

This method is abstract and should be reimplemented in any sub-class.

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

See also addWidget() and insertWidget().