QGraphicsWidget Class Reference
[QtGui module]

Detailed Description

The QGraphicsWidget class is the base class for all widget items in a QGraphicsScene.

QGraphicsWidget is an extended base item that provides extra functionality over QGraphicsItem. It is similar to QWidget in many ways:

• Provides a palette, a font and a style().
• Has a defined geometry().
• Supports layouts with setLayout() and layout().

Unlike QGraphicsItem, QGraphicsWidget is not an abstract class; you can create instances of a QGraphicsWidget without having to subclass it. This approach is useful for widgets that only serve the purpose of organizing child widgets into a layout.

QGraphicsWidget can be used as a base item for your own custom item if you require advanced input focus handling, e.g., tab focus and activation, or layouts.

Since QGraphicsWidget resembles QWidget and has similar API, it is easier to port a widget from QWidget to QGraphicsWidget, instead of QGraphicsItem.

Note: QWidget-based widgets can be directly embedded into a QGraphicsScene using QGraphicsProxyWidget.

Noticeable differences between QGraphicsWidget and QWidget are:

QGraphicsWidget supports a subset of Qt's widget attributes, (Qt::WidgetAttribute), as shown in the table below. Any attributes not listed in this table are unsupported, or otherwise unused.

Although QGraphicsWidget inherits from both QObject and QGraphicsItem, you should use the functions provided by QGraphicsItem, not QObject, to manage the relationships between parent and child items. These functions control the stacking order of items as well as their ownership.

Note: The QObject::parent() should always return 0 for QGraphicsWidgets, but this policy is not strictly defined.

See also QGraphicsProxyWidget, QGraphicsItem, and Widgets and Layouts.

Property Documentation

enabled : const bool

This property holds whether the item is enabled or not.

This property is declared in QGraphicsItem.

By default, this property is true.

See also QGraphicsItem::isEnabled() and QGraphicsItem::setEnabled().

focusPolicy : Qt::FocusPolicy

This property holds the way the widget accepts keyboard focus.

The focus policy is Qt::TabFocus if the widget accepts keyboard focus by tabbing, Qt::ClickFocus if the widget accepts focus by clicking, Qt::StrongFocus if it accepts both, and Qt::NoFocus (the default) if it does not accept focus at all.

You must enable keyboard focus for a widget if it processes keyboard events. This is normally done from the widget's constructor. For instance, the QLineEdit constructor calls setFocusPolicy(Qt::StrongFocus).

If you enable a focus policy (i.e., not Qt::NoFocus), QGraphicsWidget will automatically enable the ItemIsFocusable flag. Setting Qt::NoFocus on a widget will clear the ItemIsFocusable flag. If the widget currently has keyboard focus, the widget will automatically lose focus.

Access functions:

• Qt::FocusPolicy focusPolicy () const
• void setFocusPolicy ( Qt::FocusPolicy policy )

See also focusInEvent(), focusOutEvent(), keyPressEvent(), keyReleaseEvent(), and enabled.

font : QFont

This property holds the widgets' font.

This property provides the widget's font.

QFont consists of font properties that have been explicitly defined and properties implicitly inherited from the widget's parent. Hence, font() can return a different font compared to the one set with setFont(). This scheme allows you to define single entries in a font without affecting the font's inherited entries.

When a widget's font changes, it resolves its entries against its parent widget. If the widget does not have a parent widget, it resolves its entries against the scene. The widget then sends itself a FontChange event and notifies all its descendants so that they can resolve their fonts as well.

By default, this property contains the application's default font.

Access functions:

• QFont font () const
• void setFont ( const QFont & font )

See also QApplication::font(), QGraphicsScene::font, and QFont::resolve().

layoutDirection : Qt::LayoutDirection

This property holds the layout direction for this widget.

This property modifies this widget's and all of its descendants' Qt::WA_RightToLeft attribute. It also sets this widget's Qt::WA_SetLayoutDirection attribute.

The widget's layout direction determines the order in which the layout manager horizontally arranges subwidgets of this widget. The default value depends on the language and locale of the application, and is typically in the same direction as words are read and written. With Qt::LeftToRight, the layout starts placing subwidgets from the left side of this widget towards the right. Qt::RightToLeft does the opposite - the layout will place widgets starting from the right edge moving towards the left.

Subwidgets inherit their layout direction from the parent. Top-level widget items inherit their layout direction from QGraphicsScene::layoutDirection. If you change a widget's layout direction by calling setLayoutDirection(), the widget will send itself a LayoutDirectionChange event, and then propagate the new layout direction to all its descendants.

Access functions:

• Qt::LayoutDirection layoutDirection () const
• void setLayoutDirection ( Qt::LayoutDirection direction )
• void unsetLayoutDirection ()

See also QWidget::layoutDirection and QApplication::layoutDirection.

palette : QPalette

This property holds the widget's palette.

This property provides the widget's palette. The palette provides colors and brushes for color groups (e.g., QPalette::Button) and states (e.g., QPalette::Inactive), loosely defining the general look of the widget and its children.

QPalette consists of color groups that have been explicitly defined, and groups that are implicitly inherited from the widget's parent. Because of this, palette() can return a different palette than what has been set with setPalette(). This scheme allows you to define single entries in a palette without affecting the palette's inherited entries.

When a widget's palette changes, it resolves its entries against its parent widget, or if it doesn't have a parent widget, it resolves against the scene. It then sends itself a PaletteChange event, and notifies all its descendants so they can resolve their palettes as well.

By default, this property contains the application's default palette.

Access functions:

• QPalette palette () const
• void setPalette ( const QPalette & palette )

See also QApplication::palette(), QGraphicsScene::palette, and QPalette::resolve().

size : QSizeF

This property holds the size of the widget.

Calling setSize() resizes the widget to size bounded by minimumSize() and maximumSize(). This property only affects the widget's width and height (e.g., its right and bottom edges); the widget's position and top-left corner remains unaffected.

Resizing a widget triggers the widget to immediately receive a GraphicsSceneResize event with the widget's old and new size. If the widget has a layout assigned when this event arrives, the layout will be activated and it will automatically update any child widgets's geometry.

This property does not affect any layout of the parent widget. If the widget itself is managed by a parent layout; e.g., it has a parent widget with a layout assigned, that layout will not activate.

By default, this property contains a size with zero width and height.

Access functions:

• QSizeF size () const
• void resize ( const QSizeF & size )
• void resize ( qreal w, qreal h )

See also setGeometry(), QGraphicsSceneResizeEvent, and QGraphicsLayout.

visible : const bool

This property holds whether the item is visible or not.

This property is declared in QGraphicsItem.

By default, this property is true.

See also QGraphicsItem::isVisible(), QGraphicsItem::setVisible(), show(), and hide().

windowFlags : Qt::WindowFlags

This property holds the widget's window flags.

Window flags are a combination of a window type (e.g., Qt::Dialog) and several flags giving hints on the behavior of the window. The behavior is platform-dependent.

By default, this property contains no window flags.

Access functions:

• Qt::WindowFlags windowFlags () const
• void setWindowFlags ( Qt::WindowFlags wFlags )

windowTitle : QString

This property holds this property holds the window title (caption).

This property is only used for windows.

By default, if no title has been set, this property contains an empty string.

Access functions:

• QString windowTitle () const
• void setWindowTitle ( const QString & title )

Member Function Documentation

QGraphicsWidget::QGraphicsWidget ( QGraphicsItem * parent = 0, Qt::WindowFlags wFlags = 0 )

Constructs a QGraphicsWidget instance. The optional parent argument is passed to QGraphicsItem's constructor. The optional wFlags argument specifies the widget's window flags (e.g., whether the widget should be a window, a tool, a popup, etc).

QGraphicsWidget::~QGraphicsWidget ()

Destroys the QGraphicsWidget instance.

void QGraphicsWidget::adjustSize ()

Adjusts the size of the widget to its effective minimum size hint.

This function is called implicitly when the item is shown for the first time.

See also effectiveSizeHint() and Qt::MinimumSize.

void QGraphicsWidget::changeEvent ( QEvent * event )   [virtual protected]

This event handler can be reimplemented to handle state changes.

The state being changed in this event can be retrieved through event.

Change events include: QEvent::ActivationChange, QEvent::EnabledChange, QEvent::FontChange, QEvent::StyleChange, QEvent::PaletteChange, QEvent::ParentChange, QEvent::LayoutDirectionChange, and QEvent::ContentsRectChange.

const QObjectList & QGraphicsWidget::children () const

This function returns the same value as QObject::children(). It's provided to differentiate between the obsolete member QGraphicsItem::children() and QObject::children(). QGraphicsItem now provides childItems() instead.

bool QGraphicsWidget::close ()   [slot]

Call this function to close the widget.

Returns true if the widget was closed; otherwise returns false. This slot will first send a QCloseEvent to the widget, which may or may not accept the event. If the event was ignored, nothing happens. If the event was accepted, it will hide() the widget.

If the widget has the Qt::WA_DeleteOnClose attribute set it will be deleted.

void QGraphicsWidget::closeEvent ( QCloseEvent * event )   [virtual protected]

This event handler, for event, can be reimplemented in a subclass to receive widget close events. The default implementation accepts the event.

See also close() and QCloseEvent.

bool QGraphicsWidget::focusNextPrevChild ( bool next )   [virtual protected]

Finds a new widget to give the keyboard focus to, as appropriate for Tab and Shift+Tab, and returns true if it can find a new widget; returns false otherwise. If next is true, this function searches forward; if next is false, it searches backward.

Sometimes, you will want to reimplement this function to provide special focus handling for your widget and its subwidgets. For example, a web browser might reimplement it to move its current active link forward or backward, and call the base implementation only when it reaches the last or first link on the page.

Child widgets call focusNextPrevChild() on their parent widgets, but only the window that contains the child widgets decides where to redirect focus. By reimplementing this function for an object, you gain control of focus traversal for all child widgets.

See also focusPolicy().

QGraphicsWidget * QGraphicsWidget::focusWidget () const

If this widget, a child or descendant of this widget currently has input focus, this function will return a pointer to that widget. If no descendant has input focus, 0 is returned.

See also QWidget::focusWidget().

void QGraphicsWidget::getContentsMargins ( qreal * left, qreal * top, qreal * right, qreal * bottom ) const   [virtual]

Gets the widget's contents margins. The margins are stored in left, top, right and bottom, as pointers to qreals. Each argument can be omitted by passing 0.

Reimplemented from QGraphicsLayoutItem.

See also setContentsMargins().

void QGraphicsWidget::getWindowFrameMargins ( qreal * left, qreal * top, qreal * right, qreal * bottom ) const

Gets the widget's window frame margins. The margins are stored in left, top, right and bottom as pointers to qreals. Each argument can be omitted by passing 0.

See also setWindowFrameMargins() and windowFrameRect().

void QGraphicsWidget::grabKeyboardEvent ( QEvent * event )   [virtual protected]

This event handler, for event, can be reimplemented in a subclass to receive notifications for Qt::GrabKeyboard events.

See also grabKeyboard() and grabMouse().

void QGraphicsWidget::grabMouseEvent ( QEvent * event )   [virtual protected]

This event handler, for event, can be reimplemented in a subclass to receive notifications for Qt::GrabMouse events.

See also grabMouse() and grabKeyboard().

void QGraphicsWidget::hideEvent ( QHideEvent * event )   [virtual protected]

This event handler, for Hide events, is delivered after the widget has been hidden, for example, setVisible(false) has been called for the widget or one of its ancestors when the widget was previously shown.

You can reimplement this event handler to detect when your widget is hidden. Calling QEvent::accept() or QEvent::ignore() on event has no effect.

See also showEvent(), QWidget::hideEvent(), and ItemVisibleChange.

void QGraphicsWidget::initStyleOption ( QStyleOption * option ) const   [virtual protected]

Populates a style option object for this widget based on its current state, and stores the output in option. The default implementation populates option with the following properties.

Subclasses of QGraphicsWidget should call the base implementation, and then test the type of option using qstyleoption_cast<>() or test QStyleOption::Type before storing widget-specific options.

For example:

 void MyGroupBoxWidget::initStyleOption(QStyleOption *option) const
 {
     QGraphicsWidget::initStyleOption(option);
     if (QStyleOptionGroupBox *box = qstyleoption_cast<QStyleOptionGroupBox *>(option)) {
         // Add group box specific state.
         box->flat = isFlat();
         ...
     }
 }

See also QStyleOption::initFrom().

bool QGraphicsWidget::isActiveWindow () const

Returns true if this widget's window is in the active window, or if the widget does not have a window but is in an active scene (i.e., a scene that currently has focus).

The active window is the window that either contains a child widget that currently has input focus, or that itself has input focus.

See also QGraphicsScene::activeWindow() and QGraphicsScene::setActiveWindow().

QGraphicsLayout * QGraphicsWidget::layout () const

Returns this widget's layout, or 0 if no layout is currently managing this widget.

See also setLayout().

void QGraphicsWidget::moveEvent ( QGraphicsSceneMoveEvent * event )   [virtual protected]

This event handler, for GraphicsSceneMove events, is delivered after the widget has moved (e.g., its local position has changed).

This event is only delivered when the item is moved locally. Calling setTransform() or moving any of the item's ancestors does not affect the item's local position.

You can reimplement this event handler to detect when your widget has moved. Calling QEvent::accept() or QEvent::ignore() on event has no effect.

See also ItemPositionChange and ItemPositionHasChanged.

void QGraphicsWidget::paintWindowFrame ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 )   [virtual]

This virtual function is called by QGraphicsScene to draw the window frame for windows using painter, option, and widget, in local coordinates. The base implementation uses the current style to render the frame and title bar.

You can reimplement this function in a subclass of QGraphicsWidget to provide custom rendering of the widget's window frame.

See also QGraphicsItem::paint().

void QGraphicsWidget::polishEvent ()   [virtual protected]

This event is delivered to the item by the scene at some point after it has been constructed, but before it is shown or otherwise accessed through the scene. You can use this event handler to do last-minute initializations of the widget which require the item to be fully constructed.

The base implementation does nothing.

QRectF QGraphicsWidget::rect () const

Returns the item's local rect as a QRectF. This function is equivalent to QRectF(QPointF(), size()).

See also setGeometry() and resize().

void QGraphicsWidget::resizeEvent ( QGraphicsSceneResizeEvent * event )   [virtual protected]

This event handler, for GraphicsSceneResize events, is delivered after the widget has been resized (i.e., its local size has changed). event contains both the old and the new size.

This event is only delivered when the widget is resized locally; calling setTransform() on the widget or any of its ancestors or view, does not affect the widget's local size.

You can reimplement this event handler to detect when your widget has been resized. Calling QEvent::accept() or QEvent::ignore() on event has no effect.

See also geometry() and setGeometry().

bool QGraphicsWidget::sceneEvent ( QEvent * event )   [virtual protected]

QGraphicsWidget's implementation of sceneEvent() simply passes event to QGraphicsWidget::event(). You can handle all events for your widget in event() or in any of the convenience functions; you should not have to reimplement this function in a subclass of QGraphicsWidget.

Reimplemented from QGraphicsItem.

See also QGraphicsItem::sceneEvent().

void QGraphicsWidget::setAttribute ( Qt::WidgetAttribute attribute, bool on = true )

If on is true, this function enables attribute; otherwise attribute is disabled.

See the class documentation for QGraphicsWidget for a complete list of which attributes are supported, and what they are for.

See also testAttribute() and QWidget::setAttribute().

void QGraphicsWidget::setContentsMargins ( qreal left, qreal top, qreal right, qreal bottom )

Sets the widget's contents margins to left, top, right and bottom.

Contents margins are used by the assigned layout to define the placement of subwidgets and layouts. Margins are particularily useful for widgets that constrain subwidgets to only a section of its own geometry. For example, a group box with a layout will place subwidgets inside its frame, but below the title.

Changing a widget's contents margins will always trigger an update(), and any assigned layout will be activated automatically. The widget will then receive a ContentsRectChange event.

See also getContentsMargins() and setGeometry().

void QGraphicsWidget::setGeometry ( const QRectF & rect )   [virtual]

Sets the item's geometry to rect. The item's position and size are modified as a result of calling this function. The item is first moved, then resized.

A side effect of calling this function is that the widget will receive a move event and a resize event. Also, if the widget has a layout assigned, the layout will activate.

Reimplemented from QGraphicsLayoutItem.

See also geometry() and resize().

void QGraphicsWidget::setGeometry ( qreal x, qreal y, qreal w, qreal h )

This is an overloaded member function, provided for convenience.

This convenience function is equivalent to calling setGeometry(QRectF( x, y, w, h)).

See also geometry() and resize().

void QGraphicsWidget::setLayout ( QGraphicsLayout * layout )

Sets the layout for this widget to layout. Any existing layout manager is deleted before the new layout is assigned. If layout is 0, the widget is left without a layout. Existing subwidgets' geometries will remain unaffected.

All widgets that are currently managed by layout or all of its sublayouts, are automatically reparented to this item. The layout is then invalidated, and the child widget geometries are adjusted according to this item's geometry() and contentsMargins(). Children who are not explicitly managed by layout remain unaffected by the layout after it has been assigned to this widget.

QGraphicsWidget takes ownership of layout.

See also layout(), QGraphicsLinearLayout::addItem(), and QGraphicsLayout::invalidate().

void QGraphicsWidget::setStyle ( QStyle * style )

Sets the widget's style to style. QGraphicsWidget does not take ownership of style.

If no style is assigned, or style is 0, the widget will use QGraphicsScene::style() (if this has been set). Otherwise the widget will use QApplication::style().

This function sets the Qt::WA_SetStyle attribute if style is not 0; otherwise it clears the attribute.

See also style().

void QGraphicsWidget::setTabOrder ( QGraphicsWidget * first, QGraphicsWidget * second )   [static]

Moves the second widget around the ring of focus widgets so that keyboard focus moves from the first widget to the second widget when the Tab key is pressed.

Note that since the tab order of the second widget is changed, you should order a chain like this:

 setTabOrder(a, b); // a to b
 setTabOrder(b, c); // a to b to c
 setTabOrder(c, d); // a to b to c to d

not like this:

 // WRONG
 setTabOrder(c, d); // c to d
 setTabOrder(a, b); // a to b AND c to d
 setTabOrder(b, c); // a to b to c, but not c to d

If first is 0, this indicates that second should be the first widget to receive input focus should the scene gain Tab focus (i.e., the user hits Tab so that focus passes into the scene). If second is 0, this indicates that first should be the first widget to gain focus if the scene gained BackTab focus.

By default, tab order is defined implicitly using widget creation order.

See also focusPolicy and Keyboard Focus.

void QGraphicsWidget::setWindowFrameMargins ( qreal left, qreal top, qreal right, qreal bottom )

Sets the widget's window frame margins to left, top, right and bottom. The default frame margins are provided by the style, and they depend on the current window flags.

If you would like to draw your own window decoration, you can set your own frame margins to override the default margins.

See also unsetWindowFrameMargins(), getWindowFrameMargins(), and windowFrameRect().

void QGraphicsWidget::showEvent ( QShowEvent * event )   [virtual protected]

This event handler, for Show events, is delivered before the widget has been shown, for example, setVisible(true) has been called for the widget or one of its ancestors when the widget was previously hidden.

You can reimplement this event handler to detect when your widget is shown. Calling QEvent::accept() or QEvent::ignore() on event has no effect.

See also hideEvent(), QWidget::showEvent(), and ItemVisibleChange.

QStyle * QGraphicsWidget::style () const

Returns a pointer to the widget's style. If this widget does not have any explicitly assigned style, the scene's style is returned instead. In turn, if the scene does not have any assigned style, this function returns QApplication::style().

See also setStyle().

bool QGraphicsWidget::testAttribute ( Qt::WidgetAttribute attribute ) const

Returns true if attribute is enabled for this widget; otherwise, returns false.

See also setAttribute().

void QGraphicsWidget::ungrabKeyboardEvent ( QEvent * event )   [virtual protected]

This event handler, for event, can be reimplemented in a subclass to receive notifications for Qt::UngrabKeyboard events.

See also ungrabKeyboard() and ungrabMouse().

void QGraphicsWidget::ungrabMouseEvent ( QEvent * event )   [virtual protected]

This event handler, for event, can be reimplemented in a subclass to receive notifications for Qt::UngrabMouse events.

See also ungrabMouse() and ungrabKeyboard().

void QGraphicsWidget::unsetWindowFrameMargins ()

Resets the window frame margins to the default value, provided by the style.

See also setWindowFrameMargins(), getWindowFrameMargins(), and windowFrameRect().

void QGraphicsWidget::updateGeometry ()   [virtual protected]

If this widget is currently managed by a layout, this function notifies the layout that the widget's size hints have changed and the layout may need to resize and reposition the widget accordingly.

Call this function if the widget's sizeHint() has changed.

Reimplemented from QGraphicsLayoutItem.

See also QGraphicsLayout::invalidate().

bool QGraphicsWidget::windowFrameEvent ( QEvent * event )   [virtual protected]

This event handler, for event, receives events for the window frame if this widget is a window. Its base implementation provides support for default window frame interaction such as moving, resizing, etc.

You can reimplement this handler in a subclass of QGraphicsWidget to provide your own custom window frame interaction support.

Returns true if event has been recognized and processed; otherwise, returns false.

See also event().

QRectF QGraphicsWidget::windowFrameGeometry () const

Returns the widget's geometry in parent coordinates including any window frame.

See also windowFrameRect(), getWindowFrameMargins(), and setWindowFrameMargins().

QRectF QGraphicsWidget::windowFrameRect () const

Returns the widget's local rect including any window frame.

See also windowFrameGeometry(), getWindowFrameMargins(), and setWindowFrameMargins().

Qt::WindowFrameSection QGraphicsWidget::windowFrameSectionAt ( const QPointF & pos ) const   [virtual protected]

Returns the window frame section at position pos, or Qt::NoWindowFrameSection if there is no window frame section at this position.

This function is used in QGraphicsWidget's base implementation for window frame interaction.

You can reimplement this function if you want to customize how a window can be interactively moved or resized. For instance, if you only want to allow a window to be resized by the bottom right corner, you can reimplement this function to return Qt::NoSection for all sections except Qt::BottomRightSection.

This function was introduced in Qt 4.4.

See also windowFrameEvent(), paintWindowFrame(), and windowFrameGeometry().

Qt::WindowType QGraphicsWidget::windowType () const

Returns the widgets window type.