Add wxEventFilter and related functionality.

Allow defining event filters to globally pre-process all application events
without having to override wxApp::FilterEvent().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69794 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/eventfilter.h

@@ -0,0 +1,72 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/eventfilter.h
+// Purpose:     wxEventFilter class declaration.
+// Author:      Vadim Zeitlin
+// Created:     2011-11-21
+// RCS-ID:      $Id: wxhead.h,v 1.12 2010-04-22 12:44:51 zeitlin Exp $
+// Copyright:   (c) 2011 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_EVENTFILTER_H_
+#define _WX_EVENTFILTER_H_
+
+#include "wx/defs.h"
+
+class WXDLLIMPEXP_FWD_BASE wxEvent;
+class WXDLLIMPEXP_FWD_BASE wxEvtHandler;
+
+// ----------------------------------------------------------------------------
+// wxEventFilter is used with wxEvtHandler::AddFilter() and ProcessEvent().
+// ----------------------------------------------------------------------------
+
+class wxEventFilter
+{
+public:
+    // Possible return values for FilterEvent().
+    //
+    // Notice that the values of these enum elements are fixed due to backwards
+    // compatibility constraints.
+    enum
+    {
+        // Process event as usual.
+        Event_Skip = -1,
+
+        // Don't process the event normally at all.
+        Event_Ignore = 0,
+
+        // Event was already handled, don't process it normally.
+        Event_Processed = 1
+    };
+
+    wxEventFilter()
+    {
+        m_next = NULL;
+    }
+
+    virtual ~wxEventFilter()
+    {
+        wxASSERT_MSG( !m_next, "Forgot to call wxEvtHandler::RemoveFilter()?" );
+    }
+
+    // This method allows to filter all the events processed by the program, so
+    // you should try to return quickly from it to avoid slowing down the
+    // program to the crawl.
+    //
+    // Return value should be -1 to continue with the normal event processing,
+    // or true or false to stop further processing and pretend that the event
+    // had been already processed or won't be processed at all, respectively.
+    virtual int FilterEvent(wxEvent& event) = 0;
+
+private:
+    // Objects of this class are made to be stored in a linked list in
+    // wxEvtHandler so put the next node ponter directly in the class itself.
+    wxEventFilter* m_next;
+
+    // And provide access to it for wxEvtHandler [only].
+    friend class wxEvtHandler;
+
+    wxDECLARE_NO_COPY_CLASS(wxEventFilter);
+};
+
+#endif // _WX_EVENTFILTER_H_