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// Copyright (c) 2012 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_EVENT_TARGET_H_
#define UI_EVENTS_EVENT_TARGET_H_
#include <memory>
#include <vector>
#include "base/compiler_specific.h"
#include "base/macros.h"
#include "ui/events/event_handler.h"
#include "ui/events/events_export.h"
namespace ui {
class EventDispatcher;
class EventTargeter;
class EventTargetIterator;
class LocatedEvent;
class EVENTS_EXPORT EventTarget {
public:
class DispatcherApi {
public:
explicit DispatcherApi(EventTarget* target) : target_(target) {}
private:
DispatcherApi();
EventTarget* target_;
DISALLOW_COPY_AND_ASSIGN(DispatcherApi);
};
EventTarget();
virtual ~EventTarget();
virtual bool CanAcceptEvent(const Event& event) = 0;
// Returns the parent EventTarget in the event-target tree.
virtual EventTarget* GetParentTarget() = 0;
// Returns an iterator an EventTargeter can use to iterate over the list of
// child EventTargets.
virtual std::unique_ptr<EventTargetIterator> GetChildIterator() const = 0;
// Returns the EventTargeter that should be used to find the target for an
// event in the subtree rooted at this EventTarget.
virtual EventTargeter* GetEventTargeter() = 0;
// Updates the states in |event| (e.g. location) to be suitable for |target|,
// so that |event| can be dispatched to |target|.
virtual void ConvertEventToTarget(EventTarget* target,
LocatedEvent* event);
// Priority levels for PreTargetHandlers.
enum class Priority {
// The Accessibility level is the highest, and gets events before
// other priority levels. This allows accessibility features to
// modify events directly from the user.
kAccessibility,
// System priority EventHandlers get events before default level, and
// should be used for drag and drop, menus, etc.
kSystem,
// The default level should be used by most EventHandlers.
kDefault,
};
// Adds a handler to receive events before the target. The handler must be
// explicitly removed from the target before the handler is destroyed. The
// EventTarget does not take ownership of the handler.
void AddPreTargetHandler(EventHandler* handler,
Priority priority = Priority::kDefault);
void RemovePreTargetHandler(EventHandler* handler);
// Adds a handler to receive events after the target. The handler must be
// explicitly removed from the target before the handler is destroyed. The
// EventTarget does not take ownership of the handler.
void AddPostTargetHandler(EventHandler* handler);
void RemovePostTargetHandler(EventHandler* handler);
// Returns true if the event pre target list is empty.
bool IsPreTargetListEmpty() const;
// Sets |target_handler| as |target_handler_| and returns the old handler.
EventHandler* SetTargetHandler(EventHandler* target_handler);
protected:
EventHandler* target_handler() { return target_handler_; }
private:
friend class EventDispatcher;
friend class EventTargetTestApi;
// A handler with a priority.
struct PrioritizedHandler {
EventHandler* handler = nullptr;
Priority priority = Priority::kDefault;
bool operator<(const PrioritizedHandler& ph) const {
return priority < ph.priority;
}
};
using EventHandlerPriorityList = std::vector<PrioritizedHandler>;
// Returns the list of handlers that should receive the event before the
// target. The handlers from the outermost target are first in the list, and
// the handlers on |this| are the last in the list.
void GetPreTargetHandlers(EventHandlerList* list);
// Returns the list of handlers that should receive the event after the
// target. The handlers from the outermost target are last in the list, and
// the handlers on |this| are the first in the list.
void GetPostTargetHandlers(EventHandlerList* list);
EventHandlerPriorityList pre_target_list_;
EventHandlerList post_target_list_;
EventHandler* target_handler_;
DISALLOW_COPY_AND_ASSIGN(EventTarget);
};
} // namespace ui
#endif // UI_EVENTS_EVENT_TARGET_H_
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