Fix style inheritance with dynamically changing windows

It can happen that the parent item changes before an item gets
associated with a window.

Change-Id: I4cb65a06d363f8211b202e559c76793c71ba318a
Reviewed-by: Nikita Krupenko <krnekit@gmail.com>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

4 files changed, 56 insertions, 2 deletions

diff --git a/src/quickcontrols2/qquickstyleattached.cpp b/src/quickcontrols2/qquickstyleattached.cpp
index 8b035455..d0df79c5 100644
--- a/src/quickcontrols2/qquickstyleattached.cpp
+++ b/src/quickcontrols2/qquickstyleattached.cpp
@@ -39,6 +39,7 @@
 #include <QtCore/qfile.h>
 #include <QtCore/qsettings.h>
 #include <QtCore/qfileselector.h>
+#include <QtQuick/qquickwindow.h>
 #include <QtQuick/private/qquickitem_p.h>
 #include <QtQuickTemplates2/private/qquickpopup_p.h>
 
@@ -154,15 +155,19 @@ QQuickStyleAttached::QQuickStyleAttached(QObject *parent) : QObject(parent)
             item = popup->popupItem();
     }
 
-    if (item)
+    if (item) {
+        connect(item, &QQuickItem::windowChanged, this, &QQuickStyleAttached::itemWindowChanged);
         QQuickItemPrivate::get(item)->addItemChangeListener(this, QQuickItemPrivate::Parent);
+    }
 }
 
 QQuickStyleAttached::~QQuickStyleAttached()
 {
     QQuickItem *item = qobject_cast<QQuickItem *>(parent());
-    if (item)
+    if (item) {
+        disconnect(item, &QQuickItem::windowChanged, this, &QQuickStyleAttached::itemWindowChanged);
         QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::Parent);
+    }
 
     setParentStyle(nullptr);
 }
@@ -222,6 +227,14 @@ void QQuickStyleAttached::parentStyleChange(QQuickStyleAttached *newParent, QQui
     Q_UNUSED(oldParent);
 }
 
+void QQuickStyleAttached::itemWindowChanged(QQuickWindow *window)
+{
+    Q_UNUSED(window);
+    QQuickItem *item = qobject_cast<QQuickItem *>(sender());
+    if (item)
+        setParentStyle(findParentStyle(metaObject(), item));
+}
+
 void QQuickStyleAttached::itemParentChanged(QQuickItem *item, QQuickItem *parent)
 {
     Q_UNUSED(parent);
diff --git a/src/quickcontrols2/qquickstyleattached_p.h b/src/quickcontrols2/qquickstyleattached_p.h
index 67938290..13b816f2 100644
--- a/src/quickcontrols2/qquickstyleattached_p.h
+++ b/src/quickcontrols2/qquickstyleattached_p.h
@@ -59,6 +59,7 @@
 QT_BEGIN_NAMESPACE
 
 class QSettings;
+class QQuickWindow;
 
 class Q_QUICKCONTROLS2_PRIVATE_EXPORT QQuickStyleAttached : public QObject, public QQuickItemChangeListener
 {
@@ -80,6 +81,7 @@ protected:
 
     virtual void parentStyleChange(QQuickStyleAttached *newParent, QQuickStyleAttached *oldParent);
 
+    void itemWindowChanged(QQuickWindow *window);
     void itemParentChanged(QQuickItem *item, QQuickItem *parent) override;
 
 private:
diff --git a/tests/auto/material/data/tst_material.qml b/tests/auto/material/data/tst_material.qml
index 25b4ec98..2e7390c2 100644
--- a/tests/auto/material/data/tst_material.qml
+++ b/tests/auto/material/data/tst_material.qml
@@ -426,6 +426,25 @@ TestCase {
         window.destroy()
     }
 
+    function test_windowChange() {
+        var ldr = loader.createObject()
+        verify(ldr)
+
+        var wnd = window.createObject()
+        verify(wnd)
+
+        wnd.Material.theme = Material.Dark
+        compare(wnd.Material.theme, Material.Dark)
+
+        ldr.active = true
+        verify(ldr.item)
+        compare(ldr.item.Material.theme, Material.Light)
+
+        ldr.parent = wnd.contentItem
+        compare(ldr.item.Material.theme, Material.Dark)
+
+        wnd.destroy()
+    }
 
     function test_colors_data() {
         return [
diff --git a/tests/auto/universal/data/tst_universal.qml b/tests/auto/universal/data/tst_universal.qml
index a88f2c49..0bc0d09d 100644
--- a/tests/auto/universal/data/tst_universal.qml
+++ b/tests/auto/universal/data/tst_universal.qml
@@ -318,6 +318,26 @@ TestCase {
         window.destroy()
     }
 
+    function test_windowChange() {
+        var ldr = loader.createObject()
+        verify(ldr)
+
+        var wnd = window.createObject()
+        verify(wnd)
+
+        wnd.Universal.theme = Universal.Dark
+        compare(wnd.Universal.theme, Universal.Dark)
+
+        ldr.active = true
+        verify(ldr.item)
+        compare(ldr.item.Universal.theme, Universal.Light)
+
+        ldr.parent = wnd.contentItem
+        compare(ldr.item.Universal.theme, Universal.Dark)
+
+        wnd.destroy()
+    }
+
     function test_colors_data() {
         return [
             { tag: "accent" }, { tag: "background" }, { tag: "foreground" }