ui/events/event_rewriter.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_EVENTS_EVENT_REWRITER_H_
   6 #define UI_EVENTS_EVENT_REWRITER_H_
   7
   8 #include "base/memory/scoped_ptr.h"
   9 #include "ui/events/events_export.h"
  10
  11 namespace ui {
  12
  13 class Event;
  14
  15 // Return status of EventRewriter operations; see that class below.
  16 enum EventRewriteStatus {
  17   // Nothing was done; no rewritten event returned. Pass the original
  18   // event to later rewriters, or send it to the EventProcessor if this
  19   // was the final rewriter.
  20   EVENT_REWRITE_CONTINUE,
  21
  22   // The event has been rewritten. Send the rewritten event to the
  23   // EventProcessor instead of the original event (without sending
  24   // either to any later rewriters).
  25   EVENT_REWRITE_REWRITTEN,
  26
  27   // The event should be discarded, neither passing it to any later
  28   // rewriters nor sending it to the EventProcessor.
  29   EVENT_REWRITE_DISCARD,
  30
  31   // The event has been rewritten. As for EVENT_REWRITE_REWRITTEN,
  32   // send the rewritten event to the EventProcessor instead of the
  33   // original event (without sending either to any later rewriters).
  34   // In addition the rewriter has one or more additional new events
  35   // to be retrieved using |NextDispatchEvent()| and sent to the
  36   // EventProcessor.
  37   EVENT_REWRITE_DISPATCH_ANOTHER,
  38 };
  39
  40 // EventRewriter provides a mechanism for Events to be rewritten
  41 // before being dispatched from EventSource to EventProcessor.
  42 class EVENTS_EXPORT EventRewriter {
  43  public:
  44   virtual ~EventRewriter() {}
  45
  46   // Potentially rewrites (replaces) an event, or requests it be discarded.
  47   // or discards an event. If the rewriter wants to rewrite an event, and
  48   // dispatch another event once the rewritten event is dispatched, it should
  49   // return EVENT_REWRITE_DISPATCH_ANOTHER, and return the next event to
  50   // dispatch from |NextDispatchEvent()|.
  51   virtual EventRewriteStatus RewriteEvent(
  52       const Event& event,
  53       scoped_ptr<Event>* rewritten_event) = 0;
  54
  55   // Supplies an additional event to be dispatched. It is only valid to
  56   // call this after the immediately previous call to |RewriteEvent()|
  57   // or |NextDispatchEvent()| has returned EVENT_REWRITE_DISPATCH_ANOTHER.
  58   // Should only return either EVENT_REWRITE_REWRITTEN or
  59   // EVENT_REWRITE_DISPATCH_ANOTHER; otherwise the previous call should not
  60   // have returned EVENT_REWRITE_DISPATCH_ANOTHER.
  61   virtual EventRewriteStatus NextDispatchEvent(
  62       const Event& last_event,
  63       scoped_ptr<Event>* new_event) = 0;
  64 };
  65
  66 }  // namespace ui
  67
  68 #endif  // UI_EVENTS_EVENT_REWRITER_H_