[plasma/union] src/output/qtquick/plugin: output/quick: Inherit style from parent unless there is no parent

Git commit 44bec75315f00f28e8705d4a60b041cf72555640 by Arjen Hiemstra.
Committed on 05/08/2026 at 11:09.
Pushed by ahiemstra into branch 'master'.

output/quick: Inherit style from parent unless there is no parent

This prepares things for overriding the style for specific elements.

M  +38   -3    src/output/qtquick/plugin/QuickElement.cpp
M  +6    -2    src/output/qtquick/plugin/QuickElement.h

https://invent.kde.org/plasma/union/-/commit/44bec75315f00f28e8705d4a60b041cf72555640

diff --git a/src/output/qtquick/plugin/QuickElement.cpp b/src/output/qtquick/plugin/QuickElement.cpp
index 53f647ed..9c92f953 100644
--- a/src/output/qtquick/plugin/QuickElement.cpp
+++ b/src/output/qtquick/plugin/QuickElement.cpp
@@ -300,13 +300,17 @@ QuickElement::QuickElement(QObject *parent)
     m_element->installEventFilter(this);
 
     m_statesGroup = std::make_unique<StatesGroup>(this);
-    m_style = StyleRegistry::instance()->defaultStyle();
 
     initialize();
 
     update();
 }
 
+std::shared_ptr<Union::Style> QuickElement::style() const
+{
+    return m_style;
+}
+
 QString QuickElement::type() const
 {
     return m_element->type();
@@ -385,6 +389,7 @@ QuickElement *QuickElement::qmlAttachedProperties(QObject *parent)
 
 void QuickElement::attachedParentChange(QQuickAttachedPropertyPropagator *, QQuickAttachedPropertyPropagator *)
 {
+    updateStyleFromParent();
     update();
 }
 
@@ -423,6 +428,10 @@ void QuickElement::componentComplete()
 {
     m_completed = true;
 
+    if (!m_style) {
+        setStyle(nullptr);
+    }
+
     // Add the window this element belongs to to WindowHandler so it can update
     // it to include any required state changes. This is done here because we
     // need a hook that is both late enoguh for most of the window stuff to
@@ -457,9 +466,28 @@ void QuickElement::setActiveStates(Union::Element::States newActiveStates)
     m_element->setStates(newActiveStates);
 }
 
-std::shared_ptr<Union::Style> QuickElement::style() const
+void QuickElement::setStyle(const std::shared_ptr<Union::Style> &newStyle)
 {
-    return m_style;
+    m_style = newStyle;
+
+    if (!m_style) {
+        if (attachedParent()) {
+            auto attached = qobject_cast<QuickElement *>(attachedParent());
+            while (attached && !m_style) {
+                m_style = attached->style();
+                attached = qobject_cast<QuickElement *>(attached->attachedParent());
+            }
+        }
+
+        if (!m_style) {
+            m_style = StyleRegistry::instance()->defaultStyle();
+        }
+    }
+
+    const auto children = attachedChildren();
+    for (const auto &child : children) {
+        qobject_cast<QuickElement *>(child)->updateStyleFromParent();
+    }
 }
 
 void QuickElement::updateHints()
@@ -537,6 +565,13 @@ void QuickElement::update()
     }
 }
 
+void Quick::QuickElement::updateStyleFromParent()
+{
+    if (m_styleName.isEmpty() && attachedParent()) {
+        setStyle(qobject_cast<QuickElement *>(attachedParent())->style());
+    }
+}
+
 QuickElementUpdatedEvent::QuickElementUpdatedEvent()
     : QEvent(QuickElementUpdatedEvent::s_type)
 {
diff --git a/src/output/qtquick/plugin/QuickElement.h b/src/output/qtquick/plugin/QuickElement.h
index ba2b32cb..18165b11 100644
--- a/src/output/qtquick/plugin/QuickElement.h
+++ b/src/output/qtquick/plugin/QuickElement.h
@@ -332,6 +332,8 @@ public:
     Q_PROPERTY(QuickElement *parentElement READ parentElement NOTIFY updated)
     QuickElement *parentElement() const;
 
+    std::shared_ptr<Union::Style> style() const;
+
     /*!
      * \qmlattachedproperty string Element::type
      *
@@ -425,8 +427,6 @@ public:
 
     static QuickElement *qmlAttachedProperties(QObject *parent);
 
-    std::shared_ptr<Union::Style> style() const;
-
     void componentComplete() override;
 
 protected:
@@ -441,9 +441,11 @@ private:
     friend class ElementAttribute;
 
     void setActiveStates(Union::Element::States newActiveStates);
+    void setStyle(const std::shared_ptr<Union::Style> &newStyle);
     void updateHints();
     void updateAttributes();
     void update();
+    void updateStyleFromParent();
 
     std::shared_ptr<Union::Element> m_element;
     std::unique_ptr<StatesGroup> m_statesGroup;
@@ -452,6 +454,8 @@ private:
     QList<ElementAttribute *> m_attributes;
 
     std::unique_ptr<Union::ElementQuery> m_query;
+
+    QString m_styleName;
     std::shared_ptr<Union::Style> m_style;
 
     bool m_completed = false;