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