PySide6.QtQuickControls2.QQuickAttachedPropertyPropagator

class QQuickAttachedPropertyPropagator

The QQuickAttachedPropertyPropagator class provides a way to propagate attached properties.

Details

In QML, it is possible to attach properties and signal handlers to objects. Providing Attached Properties goes into more detail about how to expose your own C++ attached types.

QQuickAttachedPropertyPropagator provides an API to propagate attached properties from a parent object to its children, similar to font and palette propagation. It supports propagation through items, popups , and windows.

If propagation of properties is not important, consider using a C++ or QML singleton instead, as it is better suited for that use case, and is more efficient in that it only requires one QObject.

To implement a custom attached property:

1. Derive a class that exposes the attached property from QQuickAttachedPropertyPropagator .

   For example, to implement an attached MyStyle.theme property, declare the MyStyle class:

2. Call initialize() in the constructor of your class:

3. Define set/inherit/propagate/reset functions for the attached property as needed. For example, to define a theme attached property:

4. Reimplement attachedParentChange() to handle property inheritance:

5. Implement a static qmlAttachedProperties function and declare the type as an attached QML type with QML_ELEMENT and QML_ATTACHED, as detailed in Providing Attached Properties:

The complete implementation is available in Qt Quick Controls - Attached Style Properties Example .

See also

Styling Qt Quick Controls

Synopsis

Methods

• def __init__()

• def attachedChildren()

• def attachedParent()

• def initialize()

Virtual methods

• def attachedParentChange()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

__init__([parent=None])

Parameters:

parent – QObject

Constructs a QQuickAttachedPropertyPropagator with the given parent.

The parent will be used to find this object’s attached parent .

Derived classes should call initialize() in their constructor.

attachedChildren()

Return type:

.list of QQuickAttachedPropertyPropagator

This function returns the attached children of this attached object.

The attached children are used when propagating property values:

attachedParent()

Return type:

QQuickAttachedPropertyPropagator

This function returns the attached parent of this attached object.

The attached parent is used when inheriting property values:

attachedParentChange(newParent, oldParent)

Parameters:

• newParent – QQuickAttachedPropertyPropagator

• oldParent – QQuickAttachedPropertyPropagator

This function is called whenever the attached parent of this QQuickAttachedPropertyPropagator changes from oldParent to newParent.

Subclasses should reimplement this function to inherit attached properties from newParent.

initialize()

Finds and sets the attached parent for this attached object, and then does the same for its children. This must be called upon construction of the attached object in order for propagation to work.

It can be useful to read global/default values before calling this function. For example, before calling initialize(), the Imagine style checks a static “globalsInitialized” flag to see if it should read default values from QSettings. The values from that file form the basis for any attached property values that have not been explicitly set.