QQuickItem Class

import QtQuick 2.0

Rectangle {
    width: 100; height: 100

    FocusScope {
        focus: true

        TextInput {
            id: input
            focus: true
        }
    }
}

import QtQuick 2.0

Rectangle {
    width: 100; height: 100

    FocusScope {
        id: scope

        TextInput {
            id: input
            focus: true
        }
    }
}

Rectangle {
    width: 100; height: 100

    TextInput {
          id: input
          focus: true
    }
}

Item {
    Rectangle {
        color: "red"
        width: 100; height: 100
        Rectangle {
            color: "blue"
            x: 50; y: 50; width: 100; height: 100
        }
    }
}

Item {
    Rectangle {
        opacity: 0.5
        color: "red"
        width: 100; height: 100
        Rectangle {
            color: "blue"
            x: 50; y: 50; width: 100; height: 100
        }
    }
}

Rectangle {
    color: "blue"
    width: 100; height: 100
    Rectangle {
        color: "red"
        x: 25; y: 25; width: 50; height: 50
        rotation: 30
    }
}

import QtQuick 2.0

Rectangle {
    color: "blue"
    width: 100; height: 100

    Rectangle {
        color: "green"
        width: 25; height: 25
    }

    Rectangle {
        color: "red"
        x: 25; y: 25; width: 50; height: 50
        scale: 1.4
    }
}

Item {
    Rectangle {
        color: "red"
        width: 100; height: 100
    }
    Rectangle {
        color: "blue"
        x: 50; y: 50; width: 100; height: 100
    }
}

Item {
    Rectangle {
        z: 1
        color: "red"
        width: 100; height: 100
    }
    Rectangle {
        color: "blue"
        x: 50; y: 50; width: 100; height: 100
    }
}

Item {
    Rectangle {
        color: "red"
        width: 100; height: 100
        Rectangle {
            color: "blue"
            x: 50; y: 50; width: 100; height: 100
        }
    }
}

Item {
    Rectangle {
        color: "red"
        width: 100; height: 100
        Rectangle {
            z: -1
            color: "blue"
            x: 50; y: 50; width: 100; height: 100
        }
    }
}

Member Function Documentation

Defines the natural width or height of the Item if no width or height is specified.

The default implicit size for most items is 0x0, however some items have an inherent implicit size which cannot be overridden, for example, Image and Text.

Setting the implicit size is useful for defining components that have a preferred size based on their content, for example:

// Label.qml
import QtQuick 2.0

Item {
    property alias icon: image.source
    property alias label: text.text
    implicitWidth: text.implicitWidth + image.implicitWidth
    implicitHeight: Math.max(text.implicitHeight, image.implicitHeight)
    Image { id: image }
    Text {
        id: text
        wrapMode: Text.Wrap
        anchors.left: image.right; anchors.right: parent.right
        anchors.verticalCenter: parent.verticalCenter
    }
}

Note: Using implicitWidth of Text or TextEdit and setting the width explicitly incurs a performance penalty as the text must be laid out twice.

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.

This function was introduced in Qt 5.10.

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().

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 0 if there is no such item.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

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 mouse 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 onto the specified child item, and false otherwise.

See also setFiltersChildMouseEvents().

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

Reimplemented from QQmlParserStatus::classBegin().

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

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

Reimplemented from QQmlParserStatus::componentComplete().

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

[virtual] 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 overwritten in order to handle point collisions in items with custom shapes. The default implementation checks if the point is inside the item's bounding rect.

Note that this method is generally used to check whether the item is under the mouse cursor, and for that reason, the implementation of this function should be as light-weight as possible.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

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.

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.

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.

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.

See also Drag and Drag and Drop.

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

Reimplemented from QObject::event().

bool QQuickItem::filtersChildMouseEvents() const

Returns whether mouse and touch events of this item's children should be filtered through this item.

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.

[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.

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.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also activeFocus.

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.

This function was introduced in Qt 5.1.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also activeFocus and Qt::FocusReason.

[virtual protected] void QQuickItem::geometryChanged(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.

void QQuickItem::grabMouse()

Grabs the mouse input.

This item will receive all mouse events until ungrabMouse() is called. Usually this function should not be called, since accepting for example a mouse press event makes sure that the following events are delivered to the item. If an item wants to take over mouse events from the current receiver, it needs to call this function.

Warning: This function should be used with caution.

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.

Note: This function will render the item to an offscreen surface and copy that surface from the GPU's memory into the CPU's memory, which can be quite costly. For "live" preview, use layers or ShaderEffectSource.

See also QQuickWindow::grabWindow().

void QQuickItem::grabTouchPoints(const QVector<int> &ids)

Grabs the touch points specified by ids.

These touch points will be owned by the item until they are released. Alternatively, the grab can be stolen by a filtering item like Flickable. Use setKeepTouchGrab() to prevent the grab from being stolen.

See also ungrabTouchPoints() and setKeepTouchGrab().

[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.

[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.

[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.

qreal QQuickItem::implicitWidth() const

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

Note: Getter function for property implicitWidth.

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.

[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).

This function was introduced in Qt 5.7.

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.

[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.

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.

Note: Window positioning is done by the window manager and this value is treated only as a hint. So, the resulting window position may differ from what is expected.

This function was introduced in Qt 5.7.

See also Concepts - Visual Coordinates in Qt Quick.

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.

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.

Note: Window positioning is done by the window manager and this value is treated only as a hint. So, the resulting window position may differ from what is expected.

This function was introduced in Qt 5.7.

See also Concepts - Visual Coordinates in Qt Quick.

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.

[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.

[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.

[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.

[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.

See also ungrabMouse().

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.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

void QQuickItem::polish()

Schedules a polish event for this item.

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

[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 0 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.

This function was introduced in Qt 5.10.

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 mouse and touch events of this item's children should be filtered through this item.

If filter is true, childMouseEventFilter() will be called when a mouse 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 function was introduced in Qt 5.10.

See also size, setWidth, and setHeight.

QSizeF QQuickItem::size() const

Returns the size of the item.

This function was introduced in Qt 5.10.

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 0.

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.

[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::ungrabMouse()

Releases the mouse grab following a call to grabMouse().

Note that this function should only be called when the item wants to stop handling further events. There is no need to call this function after a release or cancel event since no future events will be received in any case. No move or release events will be delivered after this function was called.

void QQuickItem::ungrabTouchPoints()

Ungrabs the touch points owned by this item.

Note: there is hardly any reason to call this function. It should only be called when an item does not want to receive any further events, so no move or release events will be delivered after calling this function.

See also grabTouchPoints().

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)

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.

Warning: It is crucial that OpenGL operations and interaction with the scene graph happens exclusively on the render thread, primarily during the QQuickItem::updatePaintNode() call. The best rule of thumb is to only use classes with the "QSG" prefix inside the QQuickItem::updatePaintNode() function.

Warning: This function is called on the render thread. This means any QObjects or thread local storage that is created will have affinity to the render thread, so apply caution when doing anything other than rendering in this function. Similarly for signals, these will be emitted on the render thread and will thus often be delivered via queued connections.

Note: All classes with QSG prefix should be used solely on the scene graph's rendering thread. See Scene Graph and Rendering for more information.

See also QSGMaterial, QSGSimpleMaterial, 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.

[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.

[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.