If you create a subclass of QGraphicsLayoutItem and reimplement its virtual functions, you will enable the layout to resize and position your item along with other QGraphicsLayoutItems including QGraphicsWidget and QGraphicsLayout.
The geometry, size hint, and size policy affect the item's size and position. Calling setGeometry() will always resize and reposition the item immediately. Normally, this function is called by QGraphicsLayout after the layout has been activated, but it can also be called by the item's user at any time.
Nesting QGraphicsLayoutItems
QGraphicsLayoutItems can be nested within other QGraphicsLayoutItems, similar to layouts that can contain sublayouts. This is done either by passing a QGraphicsLayoutItem pointer to QGraphicsLayoutItem's protected constructor, or by calling setParentLayoutItem(). The parentLayoutItem() function returns a pointer to the item's layoutItem parent. If the item's parent is 0 or if the the parent does not inherit from QGraphicsItem, the parentLayoutItem() function then returns 0. isLayout() returns true if the QGraphicsLayoutItem subclass is itself a layout, or false otherwise.
Qt uses QGraphicsLayoutItem to provide layout functionality in the The Graphics View Framework, but in the future its use may spread throughout Qt itself.
See also QGraphicsWidget, QGraphicsLayout, QGraphicsLinearLayout, and QGraphicsGridLayout.
Member Function Documentation
QGraphicsLayoutItem::QGraphicsLayoutItem ( QGraphicsLayoutItem * parent = 0, bool isLayout = false )
Constructs the QGraphicsLayoutItem object. parent becomes the object's parent. If isLayout is true the item is a layout, otherwise isLayout is false.
QGraphicsLayoutItem::~QGraphicsLayoutItem () [virtual]
Destroys the QGraphicsLayoutItem object.
QRectF QGraphicsLayoutItem::contentsRect () const
Returns the contents rect in local coordinates.
The contents rect defines the subrectangle used by an associated layout when arranging subitems. This function is a convenience function that adjusts the item's geometry() by its contents margins. Note that getContentsMargins() is a virtual function that you can reimplement to return the item's contents margins.
See also getContentsMargins() and geometry().
QSizeF QGraphicsLayoutItem::effectiveSizeHint ( Qt::SizeHint which, const QSizeF & constraint = QSizeF() ) const
Returns the effective size hint for this QGraphicsLayoutItem.
which is the size hint in question. constraint is an optional argument that defines a special constrain when calculating the effective size hint. By default, constraint is QSizeF(-1, -1), which means there is no constraint to the size hint.
If you want to specify the widget's size hint for a given width or height, you can provide the fixed dimension in constraint. This is useful for widgets that can grow only either vertically or horizontally, and need to set either their width or their height to a special value.
For example, a text paragraph item fit into a column width of 200 may grow vertically. You can pass QSizeF(200, -1) as a constraint to get a suitable minimum, preferred and maximum height).
You can adjust the effective size hint by reimplementing sizeHint() in a QGraphicsLayoutItem subclass, or by calling one of the following functions: setMinimumSize(), setPreferredSize, or setMaximumSize() (or a combination of both).
This function caches each of the size hints and guarantees that sizeHint() will be called only once for each value of which - unless constraint is not specified and updateGeometry() has been called.
See also sizeHint().
QRectF QGraphicsLayoutItem::geometry () const
Returns the item's geometry (e.g., position and size) as a QRectF. This function is equivalent to QRectF(pos(), size()).
See also setGeometry().
void QGraphicsLayoutItem::getContentsMargins ( qreal * left, qreal * top, qreal * right, qreal * bottom ) const [virtual]
This virtual function provides the left, top, right and bottom contents margins for this QGraphicsLayoutItem. The default implementation assumes all contents margins are 0. The parameters point to values stored in qreals. If any of the pointers is 0, that value will not be updated.
See also QGraphicsWidget::setContentsMargins().
bool QGraphicsLayoutItem::isLayout () const
Returns true if this QGraphicsLayoutItem is a layout (e.g., is inherited by an object that arranges other QGraphicsLayoutItem objects); otherwise returns false.
See also QGraphicsLayout.
qreal QGraphicsLayoutItem::maximumHeight () const
Returns the maximum height.
See also setMaximumHeight(), setMaximumSize(), and maximumSize().
QSizeF QGraphicsLayoutItem::maximumSize () const
Returns the maximum size.
See also setMaximumSize(), minimumSize(), preferredSize(), Qt::MaximumSize, and sizeHint().
qreal QGraphicsLayoutItem::maximumWidth () const
Returns the maximum width.
See also setMaximumWidth(), setMaximumSize(), and maximumSize().
qreal QGraphicsLayoutItem::minimumHeight () const
Returns the minimum height.
See also setMinimumHeight(), setMinimumSize(), and minimumSize().
QSizeF QGraphicsLayoutItem::minimumSize () const
Returns the minimum size.
See also setMinimumSize(), preferredSize(), maximumSize(), Qt::MinimumSize, and sizeHint().
qreal QGraphicsLayoutItem::minimumWidth () const
Returns the minimum width.
See also setMinimumWidth(), setMinimumSize(), and minimumSize().
QGraphicsLayoutItem * QGraphicsLayoutItem::parentLayoutItem () const
Returns the parent of this QGraphicsLayoutItem, or 0 if there is no parent, or if the parent does not inherit from QGraphicsLayoutItem (QGraphicsLayoutItem is often used through multiple inheritance with QObject-derived classes).
See also setParentLayoutItem().
qreal QGraphicsLayoutItem::preferredHeight () const
Returns the preferred height.
See also setPreferredHeight(), setPreferredSize(), and preferredSize().
QSizeF QGraphicsLayoutItem::preferredSize () const
Returns the preferred size.
See also setPreferredSize(), minimumSize(), maximumSize(), Qt::PreferredSize, and sizeHint().
qreal QGraphicsLayoutItem::preferredWidth () const
Returns the preferred width.
See also setPreferredWidth(), setPreferredSize(), and preferredSize().
void QGraphicsLayoutItem::setGeometry ( const QRectF & rect ) [virtual]
This pure virtual function sets the geometry of the QGraphicsLayoutItem to rect, which is in parent coordinates (e.g., the top-left corner of rect is equivalent to the item's position in parent coordinates).
Reimplement this function in a subclass of QGraphicsLayoutItem to enable your item to receive geometry updates.
If rect is outside of the bounds of minimumSize and maximumSize, it will be adjusted to its closest size so that it is within the legal bounds.
See also geometry().
void QGraphicsLayoutItem::setMaximumHeight ( qreal height )
Sets the maximum height to height.
See also maximumHeight(), setMaximumSize(), and maximumSize().
void QGraphicsLayoutItem::setMaximumSize ( const QSizeF & size )
Sets the maximum size to size. This property overrides sizeHint() for Qt::MaximumSize and ensures that effectiveSizeHint() will never return a size larger than size. In order to unset the maximum size, use an invalid size.
See also maximumSize(), minimumSize(), preferredSize(), Qt::MaximumSize, and sizeHint().
void QGraphicsLayoutItem::setMaximumSize ( qreal w, qreal h )
This is an overloaded member function, provided for convenience.
This convenience function is equivalent to calling setMaximumSize(QSizeF(w, h)).
See also maximumSize(), setMinimumSize(), setPreferredSize(), and sizeHint().
void QGraphicsLayoutItem::setMaximumWidth ( qreal width )
Sets the maximum width to width.
See also maximumWidth(), setMaximumSize(), and maximumSize().
void QGraphicsLayoutItem::setMinimumHeight ( qreal height )
Sets the minimum height to height.
See also minimumHeight(), setMinimumSize(), and minimumSize().
void QGraphicsLayoutItem::setMinimumSize ( const QSizeF & size )
Sets the minimum size to size. This property overrides sizeHint() for Qt::MinimumSize and ensures that effectiveSizeHint() will never return a size smaller than size. In order to unset the minimum size, use an invalid size.
See also minimumSize(), maximumSize(), preferredSize(), Qt::MinimumSize, sizeHint(), setMinimumWidth(), and setMinimumHeight().
void QGraphicsLayoutItem::setMinimumSize ( qreal w, qreal h )
This is an overloaded member function, provided for convenience.
This convenience function is equivalent to calling setMinimumSize(QSizeF(w, h)).
See also minimumSize(), setMaximumSize(), setPreferredSize(), and sizeHint().
void QGraphicsLayoutItem::setMinimumWidth ( qreal width )
Sets the minimum width to width.
See also minimumWidth(), setMinimumSize(), and minimumSize().
void QGraphicsLayoutItem::setParentLayoutItem ( QGraphicsLayoutItem * parent )
Sets the parent of this QGraphicsLayoutItem to parent.
See also parentLayoutItem().
void QGraphicsLayoutItem::setPreferredHeight ( qreal height )
Sets the preferred height to height.
See also preferredHeight(), preferredWidth(), setPreferredSize(), and preferredSize().
void QGraphicsLayoutItem::setPreferredSize ( const QSizeF & size )
Sets the preferred size to size. This property overrides sizeHint() for Qt::PreferredSize and provides the default value for effectiveSizeHint(). In order to unset the preferred size, use an invalid size.
See also preferredSize(), minimumSize(), maximumSize(), Qt::PreferredSize, and sizeHint().
void QGraphicsLayoutItem::setPreferredSize ( qreal w, qreal h )
This is an overloaded member function, provided for convenience.
This convenience function is equivalent to calling setPreferredSize(QSizeF(w, h)).
See also preferredSize(), setMaximumSize(), setMinimumSize(), and sizeHint().
void QGraphicsLayoutItem::setPreferredWidth ( qreal width )
Sets the preferred width to width.
See also preferredWidth(), preferredHeight(), setPreferredSize(), and preferredSize().
void QGraphicsLayoutItem::setSizePolicy ( const QSizePolicy & policy )
Sets the size policy to policy. The size policy describes how the item should grow horizontally and vertically when arranged in a layout.
QGraphicsLayoutItem's default size policy is (QSizePolicy::Fixed, QSizePolicy::Fixed, QSizePolicy::DefaultType), but it is common for subclasses to change the default. For example, QGraphicsWidget defaults to (QSizePolicy::Preferred, QSizePolicy::Preferred, QSizePolicy::DefaultType).
See also sizePolicy() and QWidget::sizePolicy().
This is an overloaded member function, provided for convenience.
This function is equivalent to calling setSizePolicy(QSizePolicy(hPolicy, vPolicy, controlType)).
See also sizePolicy() and QWidget::sizePolicy().
QSizeF QGraphicsLayoutItem::sizeHint ( Qt::SizeHint which, const QSizeF & constraint = QSizeF() ) const [pure virtual protected]
This pure virtual function returns the size hint for which of the QGraphicsLayoutItem, using the width or height of constraint to constrain the output.
Reimplement this function in a subclass of QGraphicsLayoutItem to provide the necessary size hints for your items.
See also effectiveSizeHint().
QSizePolicy QGraphicsLayoutItem::sizePolicy () const
Returns the current size policy.
See also setSizePolicy() and QWidget::sizePolicy().
void QGraphicsLayoutItem::updateGeometry () [virtual]
This virtual function discards any cached size hint information. You should always call this function if you change the return value of the sizeHint() function. Subclasses must always call the base implementation when reimplementing this function.
See also effectiveSizeHint().
