Windows: Register windows for touch when a device is plugged in

Call QWindowsWindow::registerTouchWindow() for all windows when a device
is plugged in while the application is running. Guard
registerTouchWindow() against repetitive invocation and wrong window
types. This amends the crash fix 7daae2c2c706fd5d1c1ae44ace6847bc297803a0
and touch should then work.

Task-number: QTBUG-48849
Change-Id: I8b257dda144f28d60bcc5c4e369a413a90263998
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 5745fc6d19..b7a866679f 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -79,6 +79,7 @@
 #include <stdio.h>
 #include <windowsx.h>
 #include <comdef.h>
+#include <dbt.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -322,6 +323,13 @@ bool QWindowsContext::initTouch(unsigned integrationOptions)
     QWindowSystemInterface::registerTouchDevice(touchDevice);
 
     d->m_systemInfo |= QWindowsContext::SI_SupportsTouch;
+
+    // A touch device was plugged while the app is running. Register all windows for touch.
+    if (QGuiApplicationPrivate::is_app_running) {
+        for (QWindowsWindow *w : qAsConst(d->m_windows))
+            w->registerTouchWindow();
+    }
+
     return true;
 }
 
@@ -965,6 +973,13 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
     }
 
     switch (et) {
+    case QtWindows::DeviceChangeEvent:
+        if (d->m_systemInfo & QWindowsContext::SI_SupportsTouch)
+            break;
+        // See if there are any touch devices added
+        if (wParam == DBT_DEVNODES_CHANGED)
+            initTouch();
+        break;
     case QtWindows::KeyboardLayoutChangeEvent:
         if (QWindowsInputContext *wic = windowsInputContext())
             wic->handleInputLanguageChanged(wParam, lParam);