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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef UI_AURA_CLIENT_DRAG_DROP_CLIENT_OBSERVER_H_
#define UI_AURA_CLIENT_DRAG_DROP_CLIENT_OBSERVER_H_
#include "ui/aura/aura_export.h"
namespace ui {
namespace mojom {
enum class DragOperation;
} // namespace mojom
class DropTargetEvent;
} // namespace ui
namespace aura {
namespace client {
// Observes drag-and-drop sessions. NOTE: drop could be asynchronous. Therefore,
// an active async drop could be interrupted by a new drag-and-drop session. In
// this case, observers are NOT notified of the interrupted async drop.
// Some possible calling orders are listed below:
// 1. Sync/async drop completion: `OnDragStarted()` -> `OnDragUpdated()` ->
// `OnDragCompleted()` -> `OnDropCompleted()`.
// 2. Async drop cancellation: OnDragStarted()` -> `OnDragUpdated()` ->
// `OnDragCompleted()` -> `OnDragCancelled()`.
class AURA_EXPORT DragDropClientObserver {
public:
virtual ~DragDropClientObserver() = default;
// Called when dragging started.
virtual void OnDragStarted() {}
// Called when dragging is updated.
virtual void OnDragUpdated(const ui::DropTargetEvent& event) {}
// Called when dragging completes successfully.
virtual void OnDragCompleted(const ui::DropTargetEvent& event) {}
// Called when dragging is cancelled.
// NOTE:
// 1. Drag 'n drop cancellations may be processed asynchronously.
// Hence, this hook might be called before the action is actually processed.
// 2. This method is called in a disallowed async drop. In this case,
// `OnDragCancelled()` is called after `OnDragCompleted()`.
virtual void OnDragCancelled() {}
// Called when drop is completed. `drag_operation` indicates the operation
// when drop completes.
// NOTE: drop completion could be performed asynchronously. When an async drop
// is completed after a new drag-and-drop session starts, this method is not
// called for this drop.
virtual void OnDropCompleted(ui::mojom::DragOperation drag_operation) {}
#if BUILDFLAG(IS_CHROMEOS)
// Called when the set of currently selected drag operation changes during the
// drag. |action| is a bitmask of the actions selected by the client. This is
// to provide feedback during the operation, it does not take precedence over
// the operation returned from StartDragAndDrop.
virtual void OnDragActionsChanged(int actions) {}
#endif
// Called during destruction of the observed `DragDropClient`. Note that the
// client being destroyed does not necessarily imply the end of the drag
// session.
virtual void OnDragDropClientDestroying() {}
};
} // namespace client
} // namespace aura
#endif // UI_AURA_CLIENT_DRAG_DROP_CLIENT_OBSERVER_H_
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