events: Introduce PlatformEventDispatcher and PlatformEventSource.

ui/events/platform/platform_event_source.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_EVENTS_PLATFORM_PLATFORM_EVENT_SOURCE_H_
+#define UI_EVENTS_PLATFORM_PLATFORM_EVENT_SOURCE_H_
+
+#include <map>
+#include <vector>
+
+#include "base/auto_reset.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/observer_list.h"
+#include "ui/events/events_export.h"
+#include "ui/events/platform/platform_event_types.h"
+
+namespace ui {
+
+class Event;
+class PlatformEventDispatcher;
+class PlatformEventObserver;
+class ScopedEventDispatcher;
+
+// PlatformEventSource receives events from a source and dispatches the events
+// to the appropriate dispatchers.
+class EVENTS_EXPORT PlatformEventSource {
+ public:
+  virtual ~PlatformEventSource();
+
+  static PlatformEventSource* GetInstance();
+
+  void AddPlatformEventDispatcher(PlatformEventDispatcher* dispatcher);
+  void RemovePlatformEventDispatcher(PlatformEventDispatcher* dispatcher);
+
+  // Installs a PlatformEventDispatcher that receives all the events. The
+  // dispatcher can process the event, or request that the default dispatchers
+  // be invoked by setting |POST_DISPATCH_PERFORM_DEFAULT| flag from the
+  // |DispatchEvent()| override.
+  // The returned |ScopedEventDispatcher| object is a handler for the overridden
+  // dispatcher. When this handler is destroyed, it removes the overridden
+  // dispatcher, and restores the previous override-dispatcher (or NULL if there
+  // wasn't any).
+  scoped_ptr<ScopedEventDispatcher> OverrideDispatcher(
+      PlatformEventDispatcher* dispatcher);
+
+  void AddPlatformEventObserver(PlatformEventObserver* observer);
+  void RemovePlatformEventObserver(PlatformEventObserver* observer);
+
+ protected:
+  PlatformEventSource();
+
+  // Dispatches |platform_event| to the dispatchers. If there is an override
+  // dispatcher installed using |OverrideDispatcher()|, then that dispatcher
+  // receives the event first. |POST_DISPATCH_QUIT_LOOP| flag is set in the
+  // returned value if the event-source should stop dispatching events at the
+  // current message-loop iteration.
+  virtual uint32_t DispatchEvent(PlatformEvent platform_event);
+
+ private:
+  friend class ScopedEventDispatcher;
+  static PlatformEventSource* instance_;
+
+  void OnOverriddenDispatcherRestored();
+
+  // Invokes the corresponding methods on the PlatformEventObservers added to
+  // the event-source.
+  // Returns true from |WillProcessEvent()| if any of the observers in the list
+  // consumes the event and returns true from |WillProcessEvent()|.
+  bool WillProcessEvent(PlatformEvent platform_event);
+  void DidProcessEvent(PlatformEvent platform_event);
+
+  typedef std::vector<PlatformEventDispatcher*> PlatformEventDispatcherList;
+  PlatformEventDispatcherList dispatchers_;
+  PlatformEventDispatcher* overridden_dispatcher_;
+
+  // Used to keep track of whether the current override-dispatcher has been
+  // reset and a previous override-dispatcher has been restored.
+  bool overridden_dispatcher_restored_;
+
+  ObserverList<PlatformEventObserver> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(PlatformEventSource);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_PLATFORM_PLATFORM_EVENT_SOURCE_H_