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// Copyright (c) 2010 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 BASE_BASE_DROP_TARGET_H_
#define BASE_BASE_DROP_TARGET_H_
#include <objidl.h>
#include "base/ref_counted.h"
struct IDropTargetHelper;
// A DropTarget implementation that takes care of the nitty gritty
// of dnd. While this class is concrete, subclasses will most likely
// want to override various OnXXX methods.
//
// Because BaseDropTarget is ref counted you shouldn't delete it directly,
// rather wrap it in a scoped_refptr. Be sure and invoke RevokeDragDrop(m_hWnd)
// before the HWND is deleted too.
//
// This class is meant to be used in a STA and is not multithread-safe.
class BaseDropTarget : public IDropTarget {
public:
// Create a new BaseDropTarget associating it with the given HWND.
explicit BaseDropTarget(HWND hwnd);
virtual ~BaseDropTarget();
// When suspended is set to |true|, the drop target does not receive drops
// from drags initiated within the owning HWND.
bool suspended() const { return suspended_; }
void set_suspended(bool suspended) { suspended_ = suspended; }
// IDropTarget implementation:
HRESULT __stdcall DragEnter(IDataObject* data_object,
DWORD key_state,
POINTL cursor_position,
DWORD* effect);
HRESULT __stdcall DragOver(DWORD key_state,
POINTL cursor_position,
DWORD* effect);
HRESULT __stdcall DragLeave();
HRESULT __stdcall Drop(IDataObject* data_object,
DWORD key_state,
POINTL cursor_position,
DWORD* effect);
// IUnknown implementation:
HRESULT __stdcall QueryInterface(const IID& iid, void** object);
ULONG __stdcall AddRef();
ULONG __stdcall Release();
protected:
// Returns the hosting HWND.
HWND GetHWND() { return hwnd_; }
// Invoked when the cursor first moves over the hwnd during a dnd session.
// This should return a bitmask of the supported drop operations:
// DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
// DROPEFFECT_MOVE.
virtual DWORD OnDragEnter(IDataObject* data_object,
DWORD key_state,
POINT cursor_position,
DWORD effect);
// Invoked when the cursor moves over the window during a dnd session.
// This should return a bitmask of the supported drop operations:
// DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
// DROPEFFECT_MOVE.
virtual DWORD OnDragOver(IDataObject* data_object,
DWORD key_state,
POINT cursor_position,
DWORD effect);
// Invoked when the cursor moves outside the bounds of the hwnd during a
// dnd session.
virtual void OnDragLeave(IDataObject* data_object);
// Invoked when the drop ends on the window. This should return the operation
// that was taken.
virtual DWORD OnDrop(IDataObject* data_object,
DWORD key_state,
POINT cursor_position,
DWORD effect);
// Return the drag identity.
static int32 GetDragIdentity() { return drag_identity_; }
private:
// Returns the cached drop helper, creating one if necessary. The returned
// object is not addrefed. May return NULL if the object couldn't be created.
static IDropTargetHelper* DropHelper();
// The data object currently being dragged over this drop target.
scoped_refptr<IDataObject> current_data_object_;
// A helper object that is used to provide drag image support while the mouse
// is dragging over the content area.
//
// DO NOT ACCESS DIRECTLY! Use DropHelper() instead, which will lazily create
// this if it doesn't exist yet. This object can take tens of milliseconds to
// create, and we don't want to block any window opening for this, especially
// since often, DnD will never be used. Instead, we force this penalty to the
// first time it is actually used.
static IDropTargetHelper* cached_drop_target_helper_;
// The drag identity (id). An up-counter that increases when the cursor first
// moves over the HWND in a DnD session (OnDragEnter). 0 is reserved to mean
// the "no/unknown" identity, and is used for initialization. The identity is
// sent to the renderer in drag enter notifications. Note: the identity value
// is passed over the renderer NPAPI interface to gears, so use int32 instead
// of int here.
static int32 drag_identity_;
// The HWND of the source. This HWND is used to determine coordinates for
// mouse events that are sent to the renderer notifying various drag states.
HWND hwnd_;
// Whether or not we are currently processing drag notifications for drags
// initiated in this window.
bool suspended_;
LONG ref_count_;
DISALLOW_COPY_AND_ASSIGN(BaseDropTarget);
};
#endif // BASE_BASE_DROP_TARGET_H_
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