Windows tray icon: Fix reinstalling after restart of Explorer.

Use a normal instead of a HWND_MESSAGE-window since the latter
do not receive the "TaskbarCreated" message. Provide an invokable
slot in the native interface to register a window class for that
purpose.

Task-number: QTBUG-29160
Change-Id: Ic25222d08d21867f7d882a9e19d8aaf50f3f47cf
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

2 files changed, 32 insertions, 12 deletions

diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index aac28c36dc..4473b6b8a4 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -107,6 +107,9 @@ public:
     Q_INVOKABLE void *createMessageWindow(const QString &classNameTemplate,
                                           const QString &windowName,
                                           void *eventProc) const;
+
+    Q_INVOKABLE QString registerWindowClass(const QString &classNameIn, void *eventProc) const;
+
     bool asyncExpose() const;
     void setAsyncExpose(bool value);
 };
@@ -186,6 +189,15 @@ void *QWindowsNativeInterface::createMessageWindow(const QString &classNameTempl
     return hwnd;
 }
 
+/*!
+    \brief Registers a unique window class with a callback function based on \a classNameIn.
+*/
+
+QString QWindowsNativeInterface::registerWindowClass(const QString &classNameIn, void *eventProc) const
+{
+    return QWindowsContext::instance()->registerWindowClass(classNameIn, (WNDPROC)eventProc);
+}
+
 bool QWindowsNativeInterface::asyncExpose() const
 {
     return QWindowsContext::instance()->asyncExpose();
diff --git a/src/widgets/util/qsystemtrayicon_win.cpp b/src/widgets/util/qsystemtrayicon_win.cpp
index 8d8d731795..209fb206e1 100644
--- a/src/widgets/util/qsystemtrayicon_win.cpp
+++ b/src/widgets/util/qsystemtrayicon_win.cpp
@@ -166,21 +166,29 @@ extern "C" LRESULT QT_WIN_CALLBACK qWindowsTrayconWndProc(HWND hwnd, UINT messag
 }
 
 // Invoke a service of the native Windows interface to create
-// a non-visible message window.
+// a non-visible toplevel window to receive tray messages.
+// Note: Message windows (HWND_MESSAGE) are not sufficient, they
+// will not receive the "TaskbarCreated" message.
 static inline HWND createTrayIconMessageWindow()
 {
-    if (QPlatformNativeInterface *ni = QGuiApplication::platformNativeInterface()) {
-        void *hwnd = 0;
-        void *wndProc = reinterpret_cast<void *>(qWindowsTrayconWndProc);
-        if (QMetaObject::invokeMethod(ni, "createMessageWindow", Qt::DirectConnection,
-                                  Q_RETURN_ARG(void *, hwnd),
-                                  Q_ARG(QString, QStringLiteral("QTrayIconMessageWindowClass")),
-                                  Q_ARG(QString, QStringLiteral("QTrayIconMessageWindow")),
-                                  Q_ARG(void *, wndProc)) && hwnd) {
-            return reinterpret_cast<HWND>(hwnd);
-        }
+    QPlatformNativeInterface *ni = QGuiApplication::platformNativeInterface();
+    if (!ni)
+        return 0;
+    // Register window class in the platform plugin.
+    QString className;
+    void *wndProc = reinterpret_cast<void *>(qWindowsTrayconWndProc);
+    if (!QMetaObject::invokeMethod(ni, "registerWindowClass", Qt::DirectConnection,
+                                   Q_RETURN_ARG(QString, className),
+                                   Q_ARG(QString, QStringLiteral("QTrayIconMessageWindowClass")),
+                                   Q_ARG(void *, wndProc))) {
+        return 0;
     }
-    return 0;
+    const wchar_t windowName[] = L"QTrayIconMessageWindow";
+    return CreateWindowEx(0, (wchar_t*)className.utf16(),
+                          windowName, WS_OVERLAPPED,
+                          CW_USEDEFAULT, CW_USEDEFAULT,
+                          CW_USEDEFAULT, CW_USEDEFAULT,
+                          NULL, NULL, (HINSTANCE)GetModuleHandle(0), NULL);
 }
 
 QSystemTrayIconSys::QSystemTrayIconSys(HWND hwnd, QSystemTrayIcon *object)