Qt 5.6 | Qt Widgets | C++ Classes | QGraphicsItemGroup

Qt 5.6.2 Reference Documentation

# 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

- List of all members, including inherited members

## Public Functions

| QGraphicsItemGroup(QGraphicsItem *parent = Q_NULLPTR)
| ~QGraphicsItemGroup()
void | addToGroup(QGraphicsItem *item)
void | removeFromGroup(QGraphicsItem *item)

## Reimplemented Public Functions

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

- 176 public functions inherited from QGraphicsItem

### Additional Inherited Members

- 2 static public members inherited from QGraphicsItem
- 24 protected functions inherited from QGraphicsItem

## Detailed Description

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

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
      scene->destroyItemGroup(group);

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 Function Documentation

### QGraphicsItemGroup::QGraphicsItemGroup(QGraphicsItem *parent = Q_NULLPTR)

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

See also QGraphicsScene::addItem().

### 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().

### `[virtual]` QRectF QGraphicsItemGroup::boundingRect() const

Reimplemented from QGraphicsItem::boundingRect().

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

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

Reimplemented from QGraphicsItem::isObscuredBy().

### `[virtual]` QPainterPath QGraphicsItemGroup::opaqueArea() const

Reimplemented from QGraphicsItem::opaqueArea().

### `[virtual]` void QGraphicsItemGroup::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = Q_NULLPTR)

Reimplemented from QGraphicsItem::paint().

### 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().

### `[virtual]` int QGraphicsItemGroup::type() const

Reimplemented from QGraphicsItem::type().