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      1 // Copyright (c) 2011 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_BASE_DRAGDROP_DROP_TARGET_WIN_H_
      6 #define UI_BASE_DRAGDROP_DROP_TARGET_WIN_H_
      7 
      8 #include <objidl.h>
      9 
     10 #include "base/memory/ref_counted.h"
     11 #include "ui/base/ui_base_export.h"
     12 
     13 // Windows interface.
     14 struct IDropTargetHelper;
     15 
     16 namespace ui {
     17 
     18 // A DropTarget implementation that takes care of the nitty gritty
     19 // of dnd. While this class is concrete, subclasses will most likely
     20 // want to override various OnXXX methods.
     21 //
     22 // Because DropTarget is ref counted you shouldn't delete it directly,
     23 // rather wrap it in a scoped_refptr. Be sure and invoke RevokeDragDrop(m_hWnd)
     24 // before the HWND is deleted too.
     25 //
     26 // This class is meant to be used in a STA and is not multithread-safe.
     27 class UI_BASE_EXPORT DropTargetWin : public IDropTarget {
     28  public:
     29   // Create a new DropTarget associating it with the given HWND.
     30   explicit DropTargetWin(HWND hwnd);
     31   virtual ~DropTargetWin();
     32 
     33   // IDropTarget implementation:
     34   HRESULT __stdcall DragEnter(IDataObject* data_object,
     35                               DWORD key_state,
     36                               POINTL cursor_position,
     37                               DWORD* effect);
     38   HRESULT __stdcall DragOver(DWORD key_state,
     39                              POINTL cursor_position,
     40                              DWORD* effect);
     41   HRESULT __stdcall DragLeave();
     42   HRESULT __stdcall Drop(IDataObject* data_object,
     43                          DWORD key_state,
     44                          POINTL cursor_position,
     45                          DWORD* effect);
     46 
     47   // IUnknown implementation:
     48   HRESULT __stdcall QueryInterface(const IID& iid, void** object);
     49   ULONG __stdcall AddRef();
     50   ULONG __stdcall Release();
     51 
     52  protected:
     53   // Returns the hosting HWND.
     54   HWND GetHWND() { return hwnd_; }
     55 
     56   // Invoked when the cursor first moves over the hwnd during a dnd session.
     57   // This should return a bitmask of the supported drop operations:
     58   // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
     59   // DROPEFFECT_MOVE.
     60   virtual DWORD OnDragEnter(IDataObject* data_object,
     61                             DWORD key_state,
     62                             POINT cursor_position,
     63                             DWORD effect);
     64 
     65   // Invoked when the cursor moves over the window during a dnd session.
     66   // This should return a bitmask of the supported drop operations:
     67   // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
     68   // DROPEFFECT_MOVE.
     69   virtual DWORD OnDragOver(IDataObject* data_object,
     70                            DWORD key_state,
     71                            POINT cursor_position,
     72                            DWORD effect);
     73 
     74   // Invoked when the cursor moves outside the bounds of the hwnd during a
     75   // dnd session.
     76   virtual void OnDragLeave(IDataObject* data_object);
     77 
     78   // Invoked when the drop ends on the window. This should return the operation
     79   // that was taken.
     80   virtual DWORD OnDrop(IDataObject* data_object,
     81                        DWORD key_state,
     82                        POINT cursor_position,
     83                        DWORD effect);
     84 
     85  private:
     86   // Returns the cached drop helper, creating one if necessary. The returned
     87   // object is not addrefed. May return NULL if the object couldn't be created.
     88   static IDropTargetHelper* DropHelper();
     89 
     90   // The data object currently being dragged over this drop target.
     91   scoped_refptr<IDataObject> current_data_object_;
     92 
     93   // A helper object that is used to provide drag image support while the mouse
     94   // is dragging over the content area.
     95   //
     96   // DO NOT ACCESS DIRECTLY! Use DropHelper() instead, which will lazily create
     97   // this if it doesn't exist yet. This object can take tens of milliseconds to
     98   // create, and we don't want to block any window opening for this, especially
     99   // since often, DnD will never be used. Instead, we force this penalty to the
    100   // first time it is actually used.
    101   static IDropTargetHelper* cached_drop_target_helper_;
    102 
    103   // The HWND of the source. This HWND is used to determine coordinates for
    104   // mouse events that are sent to the renderer notifying various drag states.
    105   HWND hwnd_;
    106 
    107   LONG ref_count_;
    108 
    109   DISALLOW_COPY_AND_ASSIGN(DropTargetWin);
    110 };
    111 
    112 }  // namespace ui
    113 
    114 #endif  // UI_BASE_DRAGDROP_DROP_TARGET_WIN_H_
    115