QQuickAttachedPropertyPropagator Class

Member Function Documentation

[explicit] QQuickAttachedPropertyPropagator::QQuickAttachedPropertyPropagator(QObject *parent = nullptr)

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.

[virtual noexcept] QQuickAttachedPropertyPropagator::~QQuickAttachedPropertyPropagator()

Destroys the QQuickAttachedPropertyPropagator.

QList<QQuickAttachedPropertyPropagator *> QQuickAttachedPropertyPropagator::attachedChildren() const

This function returns the attached children of this attached object.

The attached children are used when propagating property values:

void MyStyle::propagateTheme()
{
    const auto styles = attachedChildren();
    for (QQuickAttachedPropertyPropagator *child : styles) {
        MyStyle *myStyle = qobject_cast<MyStyle *>(child);
        if (myStyle)
            myStyle->inheritTheme(m_theme);
    }
}

QQuickAttachedPropertyPropagator *QQuickAttachedPropertyPropagator::attachedParent() const

This function returns the attached parent of this attached object.

The attached parent is used when inheriting property values:

void MyStyle::resetTheme()
{
    if (!m_explicitTheme)
        return;

    m_explicitTheme = false;
    MyStyle *myStyle = qobject_cast<MyStyle *>(attachedParent());
    inheritTheme(myStyle ? myStyle->theme() : globalTheme);
}

[virtual protected] void QQuickAttachedPropertyPropagator::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)

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.

void MyStyle::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)
{
    Q_UNUSED(oldParent);
    MyStyle *attachedParentStyle = qobject_cast<MyStyle *>(newParent);
    if (attachedParentStyle) {
        inheritTheme(attachedParentStyle->theme());
        // Do any other inheriting here...
    }
}

[protected] void QQuickAttachedPropertyPropagator::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.

MyStyle::MyStyle(QObject *parent)
    : QQuickAttachedPropertyPropagator(parent)
    , m_theme(globalTheme)
{
    // A static function could be called here that reads globalTheme from a
    // settings file once at startup. That value would override the global
    // value. This is similar to what the Imagine and Material styles do, for
    // example.

    initialize();
}