QGraphicsItemGroup Class

The QGraphicsItemGroup class provides a container that treats a group of items as a single item. More...

Header: #include <QGraphicsItemGroup>
qmake: QT += widgets
Since: Qt 4.2
Inherits: QGraphicsItem

This class was introduced in Qt 4.2.

Public Types

enum anonymous { Type }

Public Functions

QGraphicsItemGroup(QGraphicsItem *parent = nullptr)
virtual ~QGraphicsItemGroup()
void addToGroup(QGraphicsItem *item)
void removeFromGroup(QGraphicsItem *item)

Reimplemented Public Functions

virtual QRectF boundingRect() const override
virtual bool isObscuredBy(const QGraphicsItem *item) const override
virtual QPainterPath opaqueArea() const override
virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override
virtual int type() const override

Detailed Description

A QGraphicsItemGroup is a special type of compound item that treats itself and all its children as one item (i.e., all events and geometries for all children are merged together). It's common to use item groups in presentation tools, when the user wants to group several smaller items into one big item in order to simplify moving and copying of items.

If all you want is to store items inside other items, you can use any QGraphicsItem directly by passing a suitable parent to setParentItem().

The boundingRect() function of QGraphicsItemGroup returns the bounding rectangle of all items in the item group. QGraphicsItemGroup ignores the ItemIgnoresTransformations flag on its children (i.e., with respect to the geometry of the group item, the children are treated as if they were transformable).

There are two ways to construct an item group. The easiest and most common approach is to pass a list of items (e.g., all selected items) to QGraphicsScene::createItemGroup(), which returns a new QGraphicsItemGroup item. The other approach is to manually construct a QGraphicsItemGroup item, add it to the scene calling QGraphicsScene::addItem(), and then add items to the group manually, one at a time by calling addToGroup(). To dismantle ("ungroup") an item group, you can either call QGraphicsScene::destroyItemGroup(), or you can manually remove all items from the group by calling removeFromGroup().

// Group all selected items together
QGraphicsItemGroup *group = scene->createItemGroup(scene->selecteditems());

// Destroy the group, and delete the group item

The operation of adding and removing items preserves the items' scene-relative position and transformation, as opposed to calling setParentItem(), where only the child item's parent-relative position and transformation are kept.

The addtoGroup() function reparents the target item to this item group, keeping the item's position and transformation intact relative to the scene. Visually, this means that items added via addToGroup() will remain completely unchanged as a result of this operation, regardless of the item or the group's current position or transformation; although the item's position and matrix are likely to change.

The removeFromGroup() function has similar semantics to setParentItem(); it reparents the item to the parent item of the item group. As with addToGroup(), the item's scene-relative position and transformation remain intact.

See also QGraphicsItem and Graphics View Framework.

Member Type Documentation

enum QGraphicsItemGroup::anonymous

The value returned by the virtual type() function.

QGraphicsItemGroup::Type10A graphics item group

Member Function Documentation

QGraphicsItemGroup::QGraphicsItemGroup(QGraphicsItem *parent = nullptr)

Constructs a QGraphicsItemGroup. parent is passed to QGraphicsItem's constructor.

See also QGraphicsScene::addItem().

[virtual] QGraphicsItemGroup::~QGraphicsItemGroup()

Destroys the QGraphicsItemGroup.

void QGraphicsItemGroup::addToGroup(QGraphicsItem *item)

Adds the given item and item's child items to this item group. The item and child items will be reparented to this group, but its position and transformation relative to the scene will stay intact.

See also removeFromGroup() and QGraphicsScene::createItemGroup().

[override virtual] QRectF QGraphicsItemGroup::boundingRect() const

Reimplements: QGraphicsItem::boundingRect() const.

Returns the bounding rect of this group item, and all its children.

[override virtual] bool QGraphicsItemGroup::isObscuredBy(const QGraphicsItem *item) const

Reimplements: QGraphicsItem::isObscuredBy(const QGraphicsItem *item) const.

[override virtual] QPainterPath QGraphicsItemGroup::opaqueArea() const

Reimplements: QGraphicsItem::opaqueArea() const.

[override virtual] void QGraphicsItemGroup::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr)

Reimplements: QGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget).

void QGraphicsItemGroup::removeFromGroup(QGraphicsItem *item)

Removes the specified item from this group. The item will be reparented to this group's parent item, or to 0 if this group has no parent. Its position and transformation relative to the scene will stay intact.

See also addToGroup() and QGraphicsScene::destroyItemGroup().

[override virtual] int QGraphicsItemGroup::type() const

Reimplements: QGraphicsItem::type() const.

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