interface/wx/eventfilter.h

   1 ///////////////////////////////////////////////////////////////////////////////
   2 // Name:        interface/wx/eventfilter.h
   3 // Purpose:     wxEventFilter class documentation
   4 // Author:      Vadim Zeitlin
   5 // Created:     2011-11-21
   6 // RCS-ID:      $Id$
   7 // Copyright:   (c) 2011 Vadim Zeitlin <vadim@wxwidgets.org>
   8 // Licence:     wxWindows licence
   9 ///////////////////////////////////////////////////////////////////////////////
  10
  11 /**
  12     A global event filter for pre-processing all the events generated in the
  13     program.
  14
  15     This is a very simple class which just provides FilterEvent() virtual
  16     method to be called by wxEvtHandler before starting process of any event.
  17     Thus, inheriting from this class and overriding FilterEvent() allows to
  18     capture and possibly handle or ignore all the events happening in the
  19     program. Of course, having event filters adds additional overhead to every
  20     event processing and so should not be used lightly and your FilterEvent()
  21     code should try to return as quickly as possible, especially for the events
  22     it is not interested in.
  23
  24     An example of using this class:
  25     @code
  26     // This class allows to determine the last time the user has worked with
  27     // this application:
  28     class LastActivityTimeDetector : public wxEventFilter
  29     {
  30     public:
  31         LastActivityTimeDetector()
  32         {
  33             wxEvtHandler::AddFilter(this);
  34
  35             m_last = wxDateTime::Now();
  36         }
  37
  38         virtual ~LastActivityTimeDetector()
  39         {
  40             wxEvtHandler::RemoveFilter(this);
  41         }
  42
  43         virtual int FilterEvent(wxEvent& event)
  44         {
  45             // Update the last user activity
  46             const wxEventType t = event.GetEventType();
  47             if ( t == wxEVT_KEY_DOWN || t == wxEVT_MOTION ||
  48                     t == wxEVT_LEFT_DOWN ||
  49                         t == wxEVT_RIGHT_DOWN ||
  50                             t == wxEVT_MIDDLE_DOWN )
  51             {
  52                 m_last = wxDateTime::Now();
  53             }
  54
  55             // Continue processing the event normally as well.
  56             return Event_Skip;
  57         }
  58
  59         // This function could be called periodically from some timer to
  60         // do something (e.g. hide sensitive data or log out from remote
  61         // server) if the user has been inactive for some time period.
  62         bool IsInactiveFor(const wxTimeSpan& diff) const
  63         {
  64             return wxDateTime::Now() - diff > m_last;
  65         }
  66
  67     private:
  68         wxDateTime m_last;
  69     };
  70     @endcode
  71
  72     Notice that wxApp derives from wxEventFilter and is registered as an event
  73     filter during its creation so you may also override FilterEvent() method in
  74     your wxApp-derived class and, in fact, this is often the most convenient
  75     way to do it. However creating a new class deriving directly from
  76     wxEventFilter allows to isolate the event filtering code in its own
  77     separate class and also to have several independent filters, if necessary.
  78
  79     @category{events}
  80
  81     @since 2.9.3
  82  */
  83 class wxEventFilter
  84 {
  85 public:
  86     /// Possible return values for FilterEvent().
  87     enum
  88     {
  89         /// Process event as usual.
  90         Event_Skip = -1,
  91
  92         /// Don't process the event normally at all.
  93         Event_Ignore = 0,
  94
  95         /// Event was already handled, don't process it normally.
  96         Event_Processed = 1
  97     };
  98
  99     /**
 100         Default constructor.
 101
 102         Constructor does not register this filter using
 103         wxEvtHandler::AddFilter(), it's your responsibility to do it when
 104         necessary.
 105
 106         Notice that the objects of this class can't be copied.
 107      */
 108     wxEventFilter();
 109
 110     /**
 111         Destructor.
 112
 113         You must call wxEvtHandler::RemoveFilter() before destroying this
 114         object (possibly from the derived class destructor), failure to do this
 115         is indicated by an assert unless assertions are disabled.
 116      */
 117     virtual ~wxEventFilter();
 118
 119     /**
 120         Override this method to implement event pre-processing.
 121
 122         This method allows to filter all the events processed by the program,
 123         so you should try to return quickly from it to avoid slowing down the
 124         program to the crawl.
 125
 126         Although the return type of this method is @c int, this is only due to
 127         backwards compatibility concerns and the actual return value must be
 128         one of the @c Event_XXX constants defined above:
 129             - Event_Skip to continue processing the event normally (this should
 130             be used in most cases).
 131             - Event_Ignore to not process this event at all (this can be used
 132             to suppress some events).
 133             - Event_Processed to not process this event normally but indicate
 134             that it was already processed by the event filter and so no default
 135             processing should take place neither (this should only be used if
 136             the filter really did process the event).
 137      */
 138     virtual int FilterEvent(wxEvent& event) = 0;
 139 };