ui/events/event_dispatcher.h

   1 // Copyright (c) 2012 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_DISPATCHER_H_
   6 #define UI_EVENTS_EVENT_DISPATCHER_H_
   7
   8 #include "base/auto_reset.h"
   9 #include "ui/events/event.h"
  10 #include "ui/events/event_constants.h"
  11 #include "ui/events/event_handler.h"
  12 #include "ui/events/events_export.h"
  13
  14 namespace ui {
  15
  16 class EventDispatcher;
  17 class EventTarget;
  18 class EventTargeter;
  19
  20 struct EventDispatchDetails {
  21   EventDispatchDetails()
  22       : dispatcher_destroyed(false),
  23         target_destroyed(false) {}
  24   bool dispatcher_destroyed;
  25   bool target_destroyed;
  26 };
  27
  28 class EVENTS_EXPORT EventDispatcherDelegate {
  29  public:
  30   EventDispatcherDelegate();
  31   virtual ~EventDispatcherDelegate();
  32
  33   // Returns whether an event can still be dispatched to a target. (e.g. during
  34   // event dispatch, one of the handlers may have destroyed the target, in which
  35   // case the event can no longer be dispatched to the target).
  36   virtual bool CanDispatchToTarget(EventTarget* target) = 0;
  37
  38   // Returns the event being dispatched (or NULL if no event is being
  39   // dispatched).
  40   Event* current_event();
  41
  42   // Dispatches |event| to |target|. This calls |PreDispatchEvent()| before
  43   // dispatching the event, and |PostDispatchEvent()| after the event has been
  44   // dispatched.
  45   EventDispatchDetails DispatchEvent(EventTarget* target, Event* event)
  46       WARN_UNUSED_RESULT;
  47
  48  protected:
  49   // This is called once a target has been determined for an event, right before
  50   // the event is dispatched to the target. This function may modify |event| to
  51   // prepare it for dispatch (e.g. update event flags, location etc.).
  52   virtual EventDispatchDetails PreDispatchEvent(
  53       EventTarget* target,
  54       Event* event) WARN_UNUSED_RESULT;
  55
  56   // This is called right after the event dispatch is completed.
  57   // |target| is NULL if the target was deleted during dispatch.
  58   virtual EventDispatchDetails PostDispatchEvent(
  59       EventTarget* target,
  60       const Event& event) WARN_UNUSED_RESULT;
  61
  62  private:
  63   // Dispatches the event to the target.
  64   EventDispatchDetails DispatchEventToTarget(EventTarget* target,
  65                                              Event* event) WARN_UNUSED_RESULT;
  66
  67   EventDispatcher* dispatcher_;
  68
  69   DISALLOW_COPY_AND_ASSIGN(EventDispatcherDelegate);
  70 };
  71
  72 // Dispatches events to appropriate targets.
  73 class EVENTS_EXPORT EventDispatcher {
  74  public:
  75   explicit EventDispatcher(EventDispatcherDelegate* delegate);
  76   virtual ~EventDispatcher();
  77
  78   void ProcessEvent(EventTarget* target, Event* event);
  79
  80   const Event* current_event() const { return current_event_; }
  81   Event* current_event() { return current_event_; }
  82
  83   bool delegate_destroyed() const { return !delegate_; }
  84
  85   void OnHandlerDestroyed(EventHandler* handler);
  86   void OnDispatcherDelegateDestroyed();
  87
  88  private:
  89   void DispatchEventToEventHandlers(EventHandlerList* list, Event* event);
  90
  91   // Dispatches an event, and makes sure it sets ER_CONSUMED on the
  92   // event-handling result if the dispatcher itself has been destroyed during
  93   // dispatching the event to the event handler.
  94   void DispatchEvent(EventHandler* handler, Event* event);
  95
  96   EventDispatcherDelegate* delegate_;
  97
  98   Event* current_event_;
  99
 100   EventHandlerList handler_list_;
 101
 102   DISALLOW_COPY_AND_ASSIGN(EventDispatcher);
 103 };
 104
 105 }  // namespace ui
 106
 107 #endif  // UI_EVENTS_EVENT_DISPATCHER_H_