Lazy create QmlEngine on accessing rootContext

A common usecase appears to be to set variables in the rootContext
before loading a url in a QQuickWidget. We there need to ensure there
is a QmlEngine to set variables on when this is attempted.

Change-Id: I07aff2104313eeb3fab902ea3c6043c3c82c50f7
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/quickwidgets/qquickwidget_p.h b/src/quickwidgets/qquickwidget_p.h
index f0e1f848e3..b01d634fcd 100644
--- a/src/quickwidgets/qquickwidget_p.h
+++ b/src/quickwidgets/qquickwidget_p.h
@@ -105,7 +105,7 @@ public:
     QImage grabFramebuffer() Q_DECL_OVERRIDE;
 
     void init(QQmlEngine* e = 0);
-    void ensureEngine();
+    void ensureEngine() const;
     void handleWindowChange();
     void invalidateRenderControl();
 
@@ -115,7 +115,7 @@ public:
 
     QUrl source;
 
-    QPointer<QQmlEngine> engine;
+    mutable QPointer<QQmlEngine> engine;
     QQmlComponent *component;
     QBasicTimer resizetimer;
     QQuickWindow *offscreenWindow;