QQuickItem Class

Member Function Documentation

[explicit] QQuickItem::QQuickItem(QQuickItem *parent = nullptr)

Constructs a QQuickItem with the given parent.

The parent will be used as both the visual parent and the QObject parent.

[override virtual] QQuickItem::~QQuickItem()

Destroys the QQuickItem.

bool QQuickItem::acceptHoverEvents() const

Returns whether hover events are accepted by this item.

The default value is false.

If this is false, then the item will not receive any hover events through the hoverEnterEvent(), hoverMoveEvent() and hoverLeaveEvent() functions.

See also setAcceptHoverEvents().

bool QQuickItem::acceptTouchEvents() const

Returns whether touch events are accepted by this item.

The default value is false.

If this is false, then the item will not receive any touch events through the touchEvent() function.

See also setAcceptTouchEvents().

Qt::MouseButtons QQuickItem::acceptedMouseButtons() const

Returns the mouse buttons accepted by this item.

The default value is Qt::NoButton; that is, no mouse buttons are accepted.

If an item does not accept the mouse button for a particular mouse event, the mouse event will not be delivered to the item and will be delivered to the next item in the item hierarchy instead.

See also setAcceptedMouseButtons() and acceptTouchEvents().

[virtual] QRectF QQuickItem::boundingRect() const

Returns the extents of the item in its own coordinate system: a rectangle from 0, 0 to width() and height().

[invokable] QQuickItem *QQuickItem::childAt(qreal x, qreal y) const

Returns the first visible child item found at point (x, y) within the coordinate system of this item.

Returns nullptr if there is no such item.

QList<QQuickItem *> QQuickItem::childItems() const

Returns the children of this item.

[virtual protected] bool QQuickItem::childMouseEventFilter(QQuickItem *item, QEvent *event)

Reimplement this method to filter the pointer events that are received by this item's children.

This method will only be called if filtersChildMouseEvents() is true.

Return true if the specified event should not be passed on to the specified child item, and false otherwise. If you return true, you should also accept or ignore the event, to signal if event propagation should stop or continue. The event will, however, always be sent to all childMouseEventFilters up the parent chain.

See also setFiltersChildMouseEvents().

[override virtual protected] void QQuickItem::classBegin()

Reimplements: QQmlParserStatus::classBegin().

Derived classes should call the base class method before adding their own action to perform at classBegin.

[virtual] QRectF QQuickItem::clipRect() const

Returns the rectangular area within this item that is currently visible in viewportItem(), if there is a viewport and the ItemObservesViewport flag is set; otherwise, the extents of this item in its own coordinate system: a rectangle from 0, 0 to width() and height(). This is the region intended to remain visible if clip is true. It can also be used in updatePaintNode() to limit the graphics added to the scene graph.

For example, a large drawing or a large text document might be shown in a Flickable that occupies only part of the application's Window: in that case, Flickable is the viewport item, and a custom content-rendering item may choose to omit scene graph nodes that fall outside the area that is currently visible. If the ItemObservesViewport flag is set, this area will change each time the user scrolls the content in the Flickable.

In case of nested viewport items, clipRect() is the intersection of the boundingRects of all ancestors that have the ItemIsViewport flag set, mapped to the coordinate system of this item.

See also boundingRect().

[override virtual protected] void QQuickItem::componentComplete()

Reimplements: QQmlParserStatus::componentComplete().

Derived classes should call the base class method before adding their own actions to perform at componentComplete.

[virtual invokable] bool QQuickItem::contains(const QPointF &point) const

Returns true if this item contains point, which is in local coordinates; returns false otherwise.

This function can be overridden in order to handle point collisions in items with custom shapes. The default implementation checks whether the point is inside containmentMask() if it is set, or inside the bounding box otherwise.

QCursor QQuickItem::cursor() const

Returns the cursor shape for this item.

The mouse cursor will assume this shape when it is over this item, unless an override cursor is set. See the list of predefined cursor objects for a range of useful shapes.

If no cursor shape has been set this returns a cursor with the Qt::ArrowCursor shape, however another cursor shape may be displayed if an overlapping item has a valid cursor.

See also setCursor() and unsetCursor().

[virtual protected] void QQuickItem::dragEnterEvent(QDragEnterEvent *event)

This event handler can be reimplemented in a subclass to receive drag-enter events for an item. The event information is provided by the event parameter.

Drag and drop events are only provided if the ItemAcceptsDrops flag has been set for this item.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

See also Drag and Drag and Drop.

[virtual protected] void QQuickItem::dragLeaveEvent(QDragLeaveEvent *event)

This event handler can be reimplemented in a subclass to receive drag-leave events for an item. The event information is provided by the event parameter.

Drag and drop events are only provided if the ItemAcceptsDrops flag has been set for this item.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

See also Drag and Drag and Drop.

[virtual protected] void QQuickItem::dragMoveEvent(QDragMoveEvent *event)

This event handler can be reimplemented in a subclass to receive drag-move events for an item. The event information is provided by the event parameter.

Drag and drop events are only provided if the ItemAcceptsDrops flag has been set for this item.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

See also Drag and Drag and Drop.

[virtual protected] void QQuickItem::dropEvent(QDropEvent *event)

This event handler can be reimplemented in a subclass to receive drop events for an item. The event information is provided by the event parameter.

Drag and drop events are only provided if the ItemAcceptsDrops flag has been set for this item.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

See also Drag and Drag and Drop.

[invokable, since 6.3] void QQuickItem::dumpItemTree() const

Dumps some details about the visual tree of Items starting with this item, recursively.

This function was introduced in Qt 6.3.

See also Debugging Techniques and GammaRay's Qt Quick Inspector.

[invokable, since 6.3] void QQuickItem::ensurePolished()

Calls updatePolish()

This can be useful for items such as Layouts (or Positioners) which delay calculation of their implicitWidth and implicitHeight until they receive a PolishEvent.

Normally, if e.g. a child item is added or removed to a Layout, the implicit size is not immediately calculated (this is an optimization). In some cases it might be desirable to query the implicit size of the layout right after a child item has been added. If this is the case, use this function right before querying the implicit size.

This function was introduced in Qt 6.3.

See also updatePolish() and polish().

[override virtual protected] bool QQuickItem::event(QEvent *ev)

Reimplements: QObject::event(QEvent *e).

bool QQuickItem::filtersChildMouseEvents() const

Returns whether pointer events intended for this item's children should be filtered through this item.

If both this item and a child item have acceptTouchEvents() true, then when a touch interaction occurs, this item will filter the touch event. But if either this item or the child cannot handle touch events, childMouseEventFilter() will be called with a synthesized mouse event.

See also setFiltersChildMouseEvents() and childMouseEventFilter().

QQuickItem::Flags QQuickItem::flags() const

Returns the item flags for this item.

See also setFlags() and setFlag().

[virtual protected] void QQuickItem::focusInEvent(QFocusEvent *)

This event handler can be reimplemented in a subclass to receive focus-in events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

If you do reimplement this function, you should call the base class implementation.

[virtual protected] void QQuickItem::focusOutEvent(QFocusEvent *)

This event handler can be reimplemented in a subclass to receive focus-out events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[invokable] void QQuickItem::forceActiveFocus()

Forces active focus on the item.

This method sets focus on the item and ensures that all ancestor FocusScope objects in the object hierarchy are also given focus.

The reason for the focus change will be Qt::OtherFocusReason. Use the overloaded method to specify the focus reason to enable better handling of the focus change.

See also activeFocus.

[invokable] void QQuickItem::forceActiveFocus(Qt::FocusReason reason)

This is an overloaded function.

Forces active focus on the item with the given reason.

This method sets focus on the item and ensures that all ancestor FocusScope objects in the object hierarchy are also given focus.

See also activeFocus and Qt::FocusReason.

[virtual protected, since 6.0] void QQuickItem::geometryChange(const QRectF &newGeometry, const QRectF &oldGeometry)

This function is called to handle this item's changes in geometry from oldGeometry to newGeometry. If the two geometries are the same, it doesn't do anything.

Derived classes must call the base class method within their implementation.

This function was introduced in Qt 6.0.

QSharedPointer<QQuickItemGrabResult> QQuickItem::grabToImage(const QSize &targetSize = QSize())

Grabs the item into an in-memory image.

The grab happens asynchronously and the signal QQuickItemGrabResult::ready() is emitted when the grab has been completed.

Use targetSize to specify the size of the target image. By default, the result will have the same size as item.

If the grab could not be initiated, the function returns null.

See also QQuickWindow::grabWindow().

[protected] bool QQuickItem::heightValid() const

Returns whether the height property has been set explicitly.

[virtual protected] void QQuickItem::hoverEnterEvent(QHoverEvent *event)

This event handler can be reimplemented in a subclass to receive hover-enter events for an item. The event information is provided by the event parameter.

Hover events are only provided if acceptHoverEvents() is true.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::hoverLeaveEvent(QHoverEvent *event)

This event handler can be reimplemented in a subclass to receive hover-leave events for an item. The event information is provided by the event parameter.

Hover events are only provided if acceptHoverEvents() is true.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::hoverMoveEvent(QHoverEvent *event)

This event handler can be reimplemented in a subclass to receive hover-move events for an item. The event information is provided by the event parameter.

Hover events are only provided if acceptHoverEvents() is true.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

qreal QQuickItem::implicitWidth() const

Returns the width of the item that is implied by other properties that determine the content.

See also setImplicitWidth().

[virtual protected] void QQuickItem::inputMethodEvent(QInputMethodEvent *event)

This event handler can be reimplemented in a subclass to receive input method events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual] QVariant QQuickItem::inputMethodQuery(Qt::InputMethodQuery query) const

This method is only relevant for input items.

If this item is an input item, this method should be reimplemented to return the relevant input method flags for the given query.

See also QWidget::inputMethodQuery().

bool QQuickItem::isAncestorOf(const QQuickItem *child) const

Returns true if this item is an ancestor of child (i.e., if this item is child's parent, or one of child's parent's ancestors).

See also parentItem().

[protected] bool QQuickItem::isComponentComplete() const

Returns true if construction of the QML component is complete; otherwise returns false.

It is often desirable to delay some processing until the component is completed.

See also componentComplete().

bool QQuickItem::isFocusScope() const

Returns true if this item is a focus scope, and false otherwise.

[virtual] bool QQuickItem::isTextureProvider() const

Returns true if this item is a texture provider. The default implementation returns false.

This function can be called from any thread.

[virtual protected] void QQuickItem::itemChange(QQuickItem::ItemChange change, const QQuickItem::ItemChangeData &value)

Called when change occurs for this item.

value contains extra information relating to the change, when applicable.

If you re-implement this method in a subclass, be sure to call

QQuickItem::itemChange(change, value);

typically at the end of your implementation, to ensure the windowChanged() signal will be emitted.

bool QQuickItem::keepMouseGrab() const

Returns whether mouse input should exclusively remain with this item.

See also setKeepMouseGrab().

bool QQuickItem::keepTouchGrab() const

Returns whether the touch points grabbed by this item should exclusively remain with this item.

See also setKeepTouchGrab() and keepMouseGrab().

[virtual protected] void QQuickItem::keyPressEvent(QKeyEvent *event)

This event handler can be reimplemented in a subclass to receive key press events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::keyReleaseEvent(QKeyEvent *event)

This event handler can be reimplemented in a subclass to receive key release events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[invokable] QPointF QQuickItem::mapFromGlobal(const QPointF &point) const

Maps the given point in the global screen coordinate system to the equivalent point within this item's coordinate system, and returns the mapped coordinate.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

For example, this may be helpful to add a popup to a Qt Quick component.

See also Concepts - Visual Coordinates in Qt Quick.

[invokable] QPointF QQuickItem::mapFromItem(const QQuickItem *item, const QPointF &point) const

Maps the given point in item's coordinate system to the equivalent point within this item's coordinate system, and returns the mapped coordinate.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

If item is 0, this maps point from the coordinate system of the scene.

See also Concepts - Visual Coordinates in Qt Quick.

QPointF QQuickItem::mapFromScene(const QPointF &point) const

Maps the given point in the scene's coordinate system to the equivalent point within this item's coordinate system, and returns the mapped coordinate.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

See also Concepts - Visual Coordinates in Qt Quick.

QRectF QQuickItem::mapRectFromItem(const QQuickItem *item, const QRectF &rect) const

Maps the given rect in item's coordinate system to the equivalent rectangular area within this item's coordinate system, and returns the mapped rectangle value.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

If item is 0, this maps rect from the coordinate system of the scene.

See also Concepts - Visual Coordinates in Qt Quick.

QRectF QQuickItem::mapRectFromScene(const QRectF &rect) const

Maps the given rect in the scene's coordinate system to the equivalent rectangular area within this item's coordinate system, and returns the mapped rectangle value.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

See also Concepts - Visual Coordinates in Qt Quick.

QRectF QQuickItem::mapRectToItem(const QQuickItem *item, const QRectF &rect) const

Maps the given rect in this item's coordinate system to the equivalent rectangular area within item's coordinate system, and returns the mapped rectangle value.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

If item is 0, this maps rect to the coordinate system of the scene.

See also Concepts - Visual Coordinates in Qt Quick.

QRectF QQuickItem::mapRectToScene(const QRectF &rect) const

Maps the given rect in this item's coordinate system to the equivalent rectangular area within the scene's coordinate system, and returns the mapped rectangle value.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

See also Concepts - Visual Coordinates in Qt Quick.

[invokable] QPointF QQuickItem::mapToGlobal(const QPointF &point) const

Maps the given point in this item's coordinate system to the equivalent point within global screen coordinate system, and returns the mapped coordinate.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

For example, this may be helpful to add a popup to a Qt Quick component.

See also Concepts - Visual Coordinates in Qt Quick.

[invokable] QPointF QQuickItem::mapToItem(const QQuickItem *item, const QPointF &point) const

Maps the given point in this item's coordinate system to the equivalent point within item's coordinate system, and returns the mapped coordinate.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

If item is 0, this maps point to the coordinate system of the scene.

See also Concepts - Visual Coordinates in Qt Quick.

QPointF QQuickItem::mapToScene(const QPointF &point) const

Maps the given point in this item's coordinate system to the equivalent point within the scene's coordinate system, and returns the mapped coordinate.

The following properties of the item are used in the mapping: x, y, scale, rotation, transformOrigin, and transform.

See also Concepts - Visual Coordinates in Qt Quick.

[virtual protected] void QQuickItem::mouseDoubleClickEvent(QMouseEvent *event)

This event handler can be reimplemented in a subclass to receive mouse double-click events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::mouseMoveEvent(QMouseEvent *event)

This event handler can be reimplemented in a subclass to receive mouse move events for an item. The event information is provided by the event parameter.

In order to receive mouse movement events, the preceding mouse press event must be accepted (by overriding mousePressEvent(), for example) and acceptedMouseButtons() must return the relevant mouse button.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::mousePressEvent(QMouseEvent *event)

This event handler can be reimplemented in a subclass to receive mouse press events for an item. The event information is provided by the event parameter.

In order to receive mouse press events, acceptedMouseButtons() must return the relevant mouse button.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::mouseReleaseEvent(QMouseEvent *event)

This event handler can be reimplemented in a subclass to receive mouse release events for an item. The event information is provided by the event parameter.

In order to receive mouse release events, the preceding mouse press event must be accepted (by overriding mousePressEvent(), for example) and acceptedMouseButtons() must return the relevant mouse button.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::mouseUngrabEvent()

This event handler can be reimplemented in a subclass to be notified when a mouse ungrab event has occurred on this item.

[invokable] QQuickItem *QQuickItem::nextItemInFocusChain(bool forward = true)

Returns the item in the focus chain which is next to this item. If forward is true, or not supplied, it is the next item in the forwards direction. If forward is false, it is the next item in the backwards direction.

void QQuickItem::polish()

Schedules a polish event for this item.

When the scene graph processes the request, it will call updatePolish() on this item.

See also updatePolish(), QQuickTest::qIsPolishScheduled(), and ensurePolished().

[virtual protected] void QQuickItem::releaseResources()

This function is called when an item should release graphics resources which are not already managed by the nodes returned from QQuickItem::updatePaintNode().

This happens when the item is about to be removed from the window it was previously rendering to. The item is guaranteed to have a window when the function is called.

The function is called on the GUI thread and the state of the rendering thread, when it is used, is unknown. Objects should not be deleted directly, but instead scheduled for cleanup using QQuickWindow::scheduleRenderJob().

See also Graphics Resource Handling.

QQuickItem *QQuickItem::scopedFocusItem() const

If this item is a focus scope, this returns the item in its focus chain that currently has focus.

Returns nullptr if this item is not a focus scope.

void QQuickItem::setAcceptHoverEvents(bool enabled)

If enabled is true, this sets the item to accept hover events; otherwise, hover events are not accepted by this item.

See also acceptHoverEvents().

void QQuickItem::setAcceptTouchEvents(bool enabled)

If enabled is true, this sets the item to accept touch events; otherwise, touch events are not accepted by this item.

See also acceptTouchEvents().

void QQuickItem::setAcceptedMouseButtons(Qt::MouseButtons buttons)

Sets the mouse buttons accepted by this item to buttons.

See also acceptedMouseButtons().

void QQuickItem::setCursor(const QCursor &cursor)

Sets the cursor shape for this item.

See also cursor() and unsetCursor().

void QQuickItem::setFiltersChildMouseEvents(bool filter)

Sets whether pointer events intended for this item's children should be filtered through this item.

If filter is true, childMouseEventFilter() will be called when a pointer event is triggered for a child item.

See also filtersChildMouseEvents().

void QQuickItem::setFlag(QQuickItem::Flag flag, bool enabled = true)

Enables the specified flag for this item if enabled is true; if enabled is false, the flag is disabled.

These provide various hints for the item; for example, the ItemClipsChildrenToShape flag indicates that all children of this item should be clipped to fit within the item area.

void QQuickItem::setFlags(QQuickItem::Flags flags)

Enables the specified flags for this item.

See also flags() and setFlag().

void QQuickItem::setKeepMouseGrab(bool keep)

Sets whether the mouse input should remain exclusively with this item.

This is useful for items that wish to grab and keep mouse interaction following a predefined gesture. For example, an item that is interested in horizontal mouse movement may set keepMouseGrab to true once a threshold has been exceeded. Once keepMouseGrab has been set to true, filtering items will not react to mouse events.

If keep is false, a filtering item may steal the grab. For example, Flickable may attempt to steal a mouse grab if it detects that the user has begun to move the viewport.

See also keepMouseGrab().

void QQuickItem::setKeepTouchGrab(bool keep)

Sets whether the touch points grabbed by this item should remain exclusively with this item.

This is useful for items that wish to grab and keep specific touch points following a predefined gesture. For example, an item that is interested in horizontal touch point movement may set setKeepTouchGrab to true once a threshold has been exceeded. Once setKeepTouchGrab has been set to true, filtering items will not react to the relevant touch points.

If keep is false, a filtering item may steal the grab. For example, Flickable may attempt to steal a touch point grab if it detects that the user has begun to move the viewport.

See also keepTouchGrab() and setKeepMouseGrab().

void QQuickItem::setSize(const QSizeF &size)

Sets the size of the item to size. This methods preserves any existing binding on width and height; thus any change that triggers the binding to execute again will override the set values.

See also size, setWidth, and setHeight.

QSizeF QQuickItem::size() const

Returns the size of the item.

See also setSize, width, and height.

void QQuickItem::stackAfter(const QQuickItem *sibling)

Moves the specified sibling item to the index after this item within the list of children. The order of children affects both the visual stacking order and tab focus navigation order.

Assuming the z values of both items are the same, this will cause sibling to be rendered below this item.

If both items have activeFocusOnTab set to true, this will also cause the tab focus order to change, with sibling receiving focus before this item.

The given sibling must be a sibling of this item; that is, they must have the same immediate parent.

See also Concepts - Visual Parent in Qt Quick.

void QQuickItem::stackBefore(const QQuickItem *sibling)

Moves the specified sibling item to the index before this item within the list of children. The order of children affects both the visual stacking order and tab focus navigation order.

Assuming the z values of both items are the same, this will cause sibling to be rendered above this item.

If both items have activeFocusOnTab set to true, this will also cause the tab focus order to change, with sibling receiving focus after this item.

The given sibling must be a sibling of this item; that is, they must have the same immediate parent.

See also Concepts - Visual Parent in Qt Quick.

[virtual] QSGTextureProvider *QQuickItem::textureProvider() const

Returns the texture provider for an item. The default implementation returns nullptr.

This function may only be called on the rendering thread.

[virtual protected] void QQuickItem::touchEvent(QTouchEvent *event)

This event handler can be reimplemented in a subclass to receive touch events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[virtual protected] void QQuickItem::touchUngrabEvent()

This event handler can be reimplemented in a subclass to be notified when a touch ungrab event has occurred on this item.

void QQuickItem::unsetCursor()

Clears the cursor shape for this item.

See also cursor() and setCursor().

[slot] void QQuickItem::update()

Schedules a call to updatePaintNode() for this item.

The call to QQuickItem::updatePaintNode() will always happen if the item is showing in a QQuickWindow.

Only items which specify QQuickItem::ItemHasContents are allowed to call QQuickItem::update().

[protected] void QQuickItem::updateInputMethod(Qt::InputMethodQueries queries = Qt::ImQueryInput)

Notify input method on updated query values if needed. queries indicates the changed attributes.

[virtual protected] QSGNode *QQuickItem::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *updatePaintNodeData)

Called on the render thread when it is time to sync the state of the item with the scene graph.

The function is called as a result of QQuickItem::update(), if the user has set the QQuickItem::ItemHasContents flag on the item.

The function should return the root of the scene graph subtree for this item. Most implementations will return a single QSGGeometryNode containing the visual representation of this item. oldNode is the node that was returned the last time the function was called. updatePaintNodeData provides a pointer to the QSGTransformNode associated with this QQuickItem.

QSGNode *MyItem::updatePaintNode(QSGNode *node, UpdatePaintNodeData *)
{
    QSGSimpleRectNode *n = static_cast<QSGSimpleRectNode *>(node);
    if (!n) {
        n = new QSGSimpleRectNode();
        n->setColor(Qt::red);
    }
    n->setRect(boundingRect());
    return n;
}

The main thread is blocked while this function is executed so it is safe to read values from the QQuickItem instance and other objects in the main thread.

If no call to QQuickItem::updatePaintNode() result in actual scene graph changes, like QSGNode::markDirty() or adding and removing nodes, then the underlying implementation may decide to not render the scene again as the visual outcome is identical.

See also QSGMaterial, QSGGeometryNode, QSGGeometry, QSGFlatColorMaterial, QSGTextureMaterial, QSGNode::markDirty(), and Graphics Resource Handling.

[virtual protected] void QQuickItem::updatePolish()

This function should perform any layout as required for this item.

When polish() is called, the scene graph schedules a polish event for this item. When the scene graph is ready to render this item, it calls updatePolish() to do any item layout as required before it renders the next frame.

See also ensurePolished().

QQuickItem *QQuickItem::viewportItem() const

If the ItemObservesViewport flag is set, returns the nearest parent with the ItemIsViewport flag. Returns the window's contentItem if the flag is not set, or if no other viewport item is found.

Returns nullptr only if there is no viewport item and this item is not shown in a window.

See also clipRect().

[virtual protected] void QQuickItem::wheelEvent(QWheelEvent *event)

This event handler can be reimplemented in a subclass to receive wheel events for an item. The event information is provided by the event parameter.

The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function. If you don't accept the event, call event->ignore().

[protected] bool QQuickItem::widthValid() const

Returns whether the width property has been set explicitly.

QQuickWindow *QQuickItem::window() const

Returns the window in which this item is rendered.

The item does not have a window until it has been assigned into a scene. The windowChanged() signal provides a notification both when the item is entered into a scene and when it is removed from a scene.

[signal] void QQuickItem::windowChanged(QQuickWindow *window)

This signal is emitted when the item's window changes.