Detailed Description

QDesignerMemberSheetExtension is a collection of functions that is typically used to query a widget's member functions, and to manipulate the member functions' appearance in Qt Designer's signals and slots editing mode. For example:

QDesignerMemberSheetExtension *memberSheet  = 0;
QExtensionManager manager = formEditor->extensionManager();

memberSheet = qt_extension<QDesignerMemberSheetExtension*>(manager, widget);
int index = memberSheet->indexOf(setEchoMode);
memberSheet->setVisible(index, false);

delete memberSheet;

When implementing a custom widget plugin, a pointer to Qt Designer's current QDesignerFormEditorInterface object (formEditor in the example above) is provided by the QDesignerCustomWidgetInterface::initialize() function's parameter.

The member sheet (and any other extension), can be retrieved by querying Qt Designer's extension manager using the qt_extension() function. When you want to release the extension, you only need to delete the pointer.

All widgets have a default member sheet used in Qt Designer's signals and slots editing mode with the widget's member functions. But QDesignerMemberSheetExtension also provides an interface for creating custom member sheet extensions.

Warning: Qt Designer uses the QDesignerMemberSheetExtension to facilitate the signal and slot editing mode. Whenever a connection between two widgets is requested, Qt Designer will query for the widgets' member sheet extensions. If a widget has an implemented member sheet extension, this extension will override the default member sheet.

To create a member sheet extension, your extension class must inherit from both QObject and QDesignerMemberSheetExtension. Then, since we are implementing an interface, we must ensure that it's made known to the meta object system using the Q_INTERFACES() macro:

class MyMemberSheetExtension : public QObject,
        public QDesignerMemberSheetExtension
{
    Q_OBJECT
    Q_INTERFACES(QDesignerMemberSheetExtension)

public:
    ...
}

This enables Qt Designer to use qobject_cast() to query for supported interfaces using nothing but a QObject pointer.

In Qt Designer the extensions are not created until they are required. For that reason, when implementing a member sheet extension, 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 widget's member sheet 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 member sheet extension for that widget, is found. This factory will then make an instance of the extension. If no such factory is found, Qt Designer will use the default member sheet.

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(QDesignerMemberSheetExtension))
        return 0;

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

    return 0;
}

Or you can use an existing factory, expanding the QExtensionFactory::createExtension() function to make the factory able to create a member sheet 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(QDesignerMemberSheetExtension))) {
        return new MyMemberSheetExtension(widget, parent);

    } else {
        return 0;
    }
}

For a complete example using an extension class, see Task Menu Extension example. The example shows how to create a custom widget plugin for Qt Designer, and how to to use the QDesignerTaskMenuExtension class to add custom items to Qt Designer's task menu.