- Qt 6.8
- Qt Widgets Designer Manual
- C++ Classes
- QDesignerPropertySheetExtension
- Qt 6.8.0 Reference Documentation

# QDesignerPropertySheetExtension Class

The QDesignerPropertySheetExtension class allows you to manipulate a widget's properties which is displayed in Qt Designer's property editor. More...

Header: | `#include <QDesignerPropertySheetExtension>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Designer)` `target_link_libraries(mytarget PRIVATE Qt6::Designer)`
qmake: | `QT += designer`

- List of all members, including inherited members

## Public Functions

virtual | ~QDesignerPropertySheetExtension()
virtual int | count() const = 0
virtual bool | hasReset(int index) const = 0
virtual int | indexOf(const QString &name) const = 0
virtual bool | isAttribute(int index) const = 0
virtual bool | isChanged(int index) const = 0
virtual bool | isEnabled(int index) const = 0
virtual bool | isVisible(int index) const = 0
virtual QVariant | property(int index) const = 0
virtual QString | propertyGroup(int index) const = 0
virtual QString | propertyName(int index) const = 0
virtual bool | reset(int index) = 0
virtual void | setAttribute(int index, bool attribute) = 0
virtual void | setChanged(int index, bool changed) = 0
virtual void | setProperty(int index, const QVariant &value) = 0
virtual void | setPropertyGroup(int index, const QString &group) = 0
virtual void | setVisible(int index, bool visible) = 0

## Detailed Description

QDesignerPropertySheetExtension provides a collection of functions that are typically used to query a widget's properties, and to manipulate the properties' appearance in the property editor. For example:

     QDesignerPropertySheetExtension *propertySheet = nullptr;
     QExtensionManager manager = formEditor->extensionManager();

     propertySheet = qt_extension<QDesignerPropertySheetExtension*>(manager, widget);
     int index = propertySheet->indexOf(u"margin"_s);

     propertySheet->setProperty(index, 10);
     propertySheet->setChanged(index, true);

     delete propertySheet;

Note that if you change the value of a property using the QDesignerPropertySheetExtension::setProperty() function, the undo stack is not updated. To ensure that a property's value can be reverted using the undo stack, you must use the QDesignerFormWindowCursorInterface::setProperty() function, or its buddy setWidgetProperty(), instead.

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

The property sheet, or any other extension, can be retrieved by querying Qt Widgets 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 property sheet which populates Qt Widgets Designer's property editor with the widget's properties (i.e the ones defined with the Q_PROPERTY() macro). But QDesignerPropertySheetExtension also provides an interface for creating custom property sheet extensions.

Keep the following limitations in mind:

- Qt Widgets Designer uses the QDesignerPropertySheetExtension to feed its property editor. Whenever a widget is selected in its workspace, Qt Widgets Designer will query for the widget's property sheet extension. If the selected widget has an implemented property sheet extension, this extension will override the default property sheet.
- The data types used by the property sheet for some properties are opaque custom QVariant types containing additional information instead of plain Qt data types. For example, this is the case for enumerations, flags, icons, pixmaps and strings.
- Qt Widgets Designer's property editor has no implementation for handling Q_PROPERTY types for custom types that have been declared with Q_DECLARE_METATYPE().

To create a property sheet extension, your extension class must inherit from both QObject and QDesignerPropertySheetExtension. 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 MyPropertySheetExtension : public QObject,
             public QDesignerPropertySheetExtension
     {
         Q_OBJECT
         Q_INTERFACES(QDesignerPropertySheetExtension)

     public:
         ...
     }

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

In Qt Widgets Designer the extensions are not created until they are required. For that reason, when implementing a property 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 Widgets Designer's extension manager.

When a property sheet extension is required, Qt Widgets 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 property sheet extension for the selected widget, is found. This factory will then make an instance of the extension. If no such factory can be found, Qt Widgets Designer will use the default property sheet.

There are four available types of extensions in Qt Widgets 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(QDesignerPropertySheetExtension))
             return 0;

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

         return 0;
     }

Or you can use an existing factory, expanding the QExtensionFactory::createExtension() function to make the factory able to create a property 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(QDesignerPropertySheetExtension))) {
             return new MyPropertySheetExtension(widget, parent);

         } else {
             return 0;
         }
     }

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

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

## Member Function Documentation

### `[virtual constexpr noexcept]` QDesignerPropertySheetExtension::~QDesignerPropertySheetExtension()

Destroys the property sheet extension.

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

Returns the selected widget's number of properties.

### `[pure virtual]` bool QDesignerPropertySheetExtension::hasReset(int index) const

Returns true if the property at the given index has a reset button in Qt Widgets Designer's property editor, otherwise false.

See also indexOf() and reset().

### `[pure virtual]` int QDesignerPropertySheetExtension::indexOf(const QString &name) const

Returns the index for a given property name.

See also propertyName().

### `[pure virtual]` bool QDesignerPropertySheetExtension::isAttribute(int index) const

Returns true if the property at the given index is an attribute, which will be excluded from the UI file, otherwise false.

See also indexOf() and setAttribute().

### `[pure virtual]` bool QDesignerPropertySheetExtension::isChanged(int index) const

Returns true if the value of the property at the given index differs from the property's default value, otherwise false.

See also indexOf(), setChanged(), and reset().

### `[pure virtual]` bool QDesignerPropertySheetExtension::isEnabled(int index) const

Returns true if the property at the given index is enabled in Qt Widgets Designer's property editor, otherwise false.

See also indexOf().

### `[pure virtual]` bool QDesignerPropertySheetExtension::isVisible(int index) const

Returns true if the property at the given index is visible in Qt Widgets Designer's property editor, otherwise false.

See also indexOf() and setVisible().

### `[pure virtual]` QVariant QDesignerPropertySheetExtension::property(int index) const

Returns the value of the property at the given index.

See also indexOf(), setProperty(), and propertyGroup().

### `[pure virtual]` QString QDesignerPropertySheetExtension::propertyGroup(int index) const

Returns the property group for the property at the given index.

Qt Widgets Designer's property editor supports property groups, i.e. sections of related properties. A property can be related to a group using the setPropertyGroup() function. The default group of any property is the name of the class that defines it. For example, the QObject::objectName property appears within the QObject property group.

See also indexOf() and setPropertyGroup().

### `[pure virtual]` QString QDesignerPropertySheetExtension::propertyName(int index) const

Returns the name of the property at the given index.

See also indexOf().

### `[pure virtual]` bool QDesignerPropertySheetExtension::reset(int index)

Resets the value of the property at the given index, to the default value. Returns true if a default value could be found, otherwise false.

See also indexOf(), hasReset(), and isChanged().

### `[pure virtual]` void QDesignerPropertySheetExtension::setAttribute(int index, bool attribute)

If attribute is true, the property at the given index is made an attribute which will be excluded from the UI file; otherwise it will be included.

See also indexOf() and isAttribute().

### `[pure virtual]` void QDesignerPropertySheetExtension::setChanged(int index, bool changed)

Sets whether the property at the given index is different from its default value, or not, depending on the changed parameter.

See also indexOf() and isChanged().

### `[pure virtual]` void QDesignerPropertySheetExtension::setProperty(int index, const QVariant &value)

Sets the value of the property at the given index.

Warning: If you change the value of a property using this function, the undo stack is not updated. To ensure that a property's value can be reverted using the undo stack, you must use the QDesignerFormWindowCursorInterface::setProperty() function, or its buddy setWidgetProperty(), instead.

See also indexOf(), property(), and propertyGroup().

### `[pure virtual]` void QDesignerPropertySheetExtension::setPropertyGroup(int index, const QString &group)

Sets the property group for the property at the given index to group.

Relating a property to a group makes it appear within that group's section in the property editor. The default property group of any property is the name of the class that defines it. For example, the QObject::objectName property appears within the QObject property group.

See also indexOf(), property(), and propertyGroup().

### `[pure virtual]` void QDesignerPropertySheetExtension::setVisible(int index, bool visible)

If visible is true, the property at the given index is visible in Qt Widgets Designer's property editor; otherwise the property is hidden.

See also indexOf() and isVisible().