ui/base/dragdrop/drop_target_win.h

   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) override;
  38   HRESULT __stdcall DragOver(DWORD key_state,
  39                              POINTL cursor_position,
  40                              DWORD* effect) override;
  41   HRESULT __stdcall DragLeave() override;
  42   HRESULT __stdcall Drop(IDataObject* data_object,
  43                          DWORD key_state,
  44                          POINTL cursor_position,
  45                          DWORD* effect) override;
  46
  47   // IUnknown implementation:
  48   HRESULT __stdcall QueryInterface(const IID& iid, void** object) override;
  49   ULONG __stdcall AddRef() override;
  50   ULONG __stdcall Release() override;
  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_