Don't send selection events for an already selected item in wxMSW wxListBox.

Remember the last item for which a listbox notification event had been sent
and don't send it again if the user clicks on an already selected item. This
is consistent with wxGTK behaviour and generally makes more sense: why should
we send an event if the selection didn't really change?

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64500 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/listbox.cpp

@@ -686,7 +686,27 @@ bool wxListBox::MSWCommand(WXUINT param, WXWORD WXUNUSED(id))
 
     // We get events even when mouse is clicked outside of any valid item from
     // Windows, just ignore them.
-    return n != wxNOT_FOUND && SendEvent(evtType, n, true /* selection */);
+    if ( n == wxNOT_FOUND )
+       return false;
+
+    // As we don't use m_oldSelections in single selection mode, we store the
+    // last item that we notified the user about in it in this case because we
+    // need to remember it to be able to filter out the dummy LBN_SELCHANGE
+    // messages that we get when the user clicks on an already selected item.
+    if ( param == LBN_SELCHANGE )
+    {
+        if ( !m_oldSelections.empty() && *m_oldSelections.begin() == n )
+        {
+            // Same item as the last time.
+            return false;
+        }
+
+        m_oldSelections.clear();
+        m_oldSelections.push_back(n);
+    }
+
+    // Do generate an event otherwise.
+    return SendEvent(evtType, n, true /* selection */);
 }
 
 WXLRESULT