Create and init QQuickTheme from QtQuickControls2Plugin

Instead of creating and setting the QQuickTheme instance from each
style plugin (e.g. QtQuickControls2MaterialStylePlugin), create the
QQuickTheme instance in QtQuickControls2Plugin when the style is
being resolved, and just pass the instance to be initialized by the
style plugin(s). This avoids the problem that QQuickTheme API was
virtual, and sub-classes created from plugins would have vtables
destroyed before the QQuickTheme was destroyed.

Task-number: QTBUG-67062
Task-number: QTBUG-68087
Change-Id: I19e9ced5296b708c2668c30163389cb3da6be7cf
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

3 files changed, 12 insertions, 9 deletions

diff --git a/src/imports/controls/fusion/qquickfusiontheme.cpp b/src/imports/controls/fusion/qquickfusiontheme.cpp
index 78465b6b..ac88563a 100644
--- a/src/imports/controls/fusion/qquickfusiontheme.cpp
+++ b/src/imports/controls/fusion/qquickfusiontheme.cpp
@@ -36,10 +36,13 @@
 
 #include "qquickfusiontheme_p.h"
 
+#include <QtQuickTemplates2/private/qquicktheme_p.h>
+
 QT_BEGIN_NAMESPACE
 
-QQuickFusionTheme::QQuickFusionTheme()
+void QQuickFusionTheme::initialize(QQuickTheme *theme)
 {
+    Q_UNUSED(theme);
 }
 
 QT_END_NAMESPACE
diff --git a/src/imports/controls/fusion/qquickfusiontheme_p.h b/src/imports/controls/fusion/qquickfusiontheme_p.h
index 0cd77f77..814c1919 100644
--- a/src/imports/controls/fusion/qquickfusiontheme_p.h
+++ b/src/imports/controls/fusion/qquickfusiontheme_p.h
@@ -48,16 +48,16 @@
 // We mean it.
 //
 
-#include <QtCore/qvariant.h>
-#include <QtGui/qpalette.h>
-#include <QtQuickTemplates2/private/qquicktheme_p.h>
+#include <QtCore/qglobal.h>
 
 QT_BEGIN_NAMESPACE
 
-class QQuickFusionTheme :  public QQuickTheme
+class QQuickTheme;
+
+class QQuickFusionTheme
 {
 public:
-    explicit QQuickFusionTheme();
+    static void initialize(QQuickTheme *theme);
 };
 
 QT_END_NAMESPACE
diff --git a/src/imports/controls/fusion/qtquickcontrols2fusionstyleplugin.cpp b/src/imports/controls/fusion/qtquickcontrols2fusionstyleplugin.cpp
index 65da8cd7..107b4a2d 100644
--- a/src/imports/controls/fusion/qtquickcontrols2fusionstyleplugin.cpp
+++ b/src/imports/controls/fusion/qtquickcontrols2fusionstyleplugin.cpp
@@ -63,7 +63,7 @@ public:
     void registerTypes(const char *uri) override;
 
     QString name() const override;
-    QQuickTheme *createTheme() const override;
+    void initializeTheme(QQuickTheme *theme) override;
 };
 
 QtQuickControls2FusionStylePlugin::QtQuickControls2FusionStylePlugin(QObject *parent) : QQuickStylePlugin(parent)
@@ -97,9 +97,9 @@ QString QtQuickControls2FusionStylePlugin::name() const
     return QStringLiteral("Fusion");
 }
 
-QQuickTheme *QtQuickControls2FusionStylePlugin::createTheme() const
+void QtQuickControls2FusionStylePlugin::initializeTheme(QQuickTheme *theme)
 {
-    return new QQuickFusionTheme;
+    QQuickFusionTheme::initialize(theme);
 }
 
 QT_END_NAMESPACE