Lazily create QPlatformWindow for Qt::Desktop windows

QDesktopWidget only needs a QWindow to access its screen, and has no use
for the platform window. To keep old code working that may have called
winId() on the QDekstopWidget we still ensure it gets created lazily,
even if that will just create hidden fake windows on many platforms.

Change-Id: I2d05b96dfeebeaf3f1278cfef6301ef4cb855a57
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 12 insertions, 7 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index d35ad87c8d..dc55c2d5d9 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -1477,10 +1477,12 @@ void QWidgetPrivate::create_sys(WId window, bool initializeWindow, bool destroyO
 
     qt_window_private(win)->positionPolicy = topData()->posIncludesFrame ?
         QWindowPrivate::WindowFrameInclusive : QWindowPrivate::WindowFrameExclusive;
-    win->create();
-    // Enable nonclient-area events for QDockWidget and other NonClientArea-mouse event processing.
-    if ((flags & Qt::Desktop) == Qt::Window)
+
+    if (q->windowType() != Qt::Desktop || q->testAttribute(Qt::WA_NativeWindow)) {
+        win->create();
+        // Enable nonclient-area events for QDockWidget and other NonClientArea-mouse event processing.
         win->handle()->setFrameStrutEventsEnabled(true);
+    }
 
     data.window_flags = win->flags();
     if (!win->isTopLevel()) // In a Widget world foreign windows can only be top level
@@ -1501,10 +1503,13 @@ void QWidgetPrivate::create_sys(WId window, bool initializeWindow, bool destroyO
     }
 
     setWindowModified_helper();
-    WId id = win->winId();
-    // See the QPlatformWindow::winId() documentation
-    Q_ASSERT(id != WId(0));
-    setWinId(id);
+
+    if (win->handle()) {
+        WId id = win->winId();
+        // See the QPlatformWindow::winId() documentation
+        Q_ASSERT(id != WId(0));
+        setWinId(id);
+    }
 
     // Check children and create windows for them if necessary
     q_createNativeChildrenAndSetParent(q);