Add QPlatformWindow::initialize() for two-step window creation

The QWindow::create method calls createPlatformWindow, and assigns the
result to d->platformWindow. If the platform sends any sort of events
synchronously during the creation, the event will be delivered to a
QWindow that doesn't have a handle() yet, resulting in noop handling
of the event, or crashes.

To mitigate this situations, platforms should do as little a possible
in the QPlatformWindow constructor, and leave initialization to the
new method, where the QWindow will have a handle().

The macOS platform plugin still has a m_initialized guard, to prevent
sending geometry changes during initialization, as this will result
in a resize event before a show event. This forced behavior seems
dubious, but is left for a followup patch.

Task-number: QTBUG-61977
Change-Id: I04d32d93391e89d068752b719270438e7024ad46
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/gui/kernel/qplatformwindow.cpp b/src/gui/kernel/qplatformwindow.cpp
index a26a23243d..5ece421ea5 100644
--- a/src/gui/kernel/qplatformwindow.cpp
+++ b/src/gui/kernel/qplatformwindow.cpp
@@ -71,6 +71,17 @@ QPlatformWindow::~QPlatformWindow()
 }
 
 /*!
+    Called as part of QWindow::create(), after constructing
+    the window. Platforms should prefer to do initialization
+    here instead of in the constructor, as the platform window
+    object will be fully constructed, and associated to the
+    corresponding QWindow, allowing synchronous event delivery.
+*/
+void QPlatformWindow::initialize()
+{
+}
+
+/*!
     Returns the window which belongs to the QPlatformWindow
 */
 QWindow *QPlatformWindow::window() const