base/base_drop_target.h

   1 // Copyright (c) 2006-2008 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 BASE_BASE_DROP_TARGET_H_
   6 #define BASE_BASE_DROP_TARGET_H_
   7
   8 #include <objidl.h>
   9
  10 #include "base/ref_counted.h"
  11
  12 struct IDropTargetHelper;
  13
  14 // A DropTarget implementation that takes care of the nitty gritty
  15 // of dnd. While this class is concrete, subclasses will most likely
  16 // want to override various OnXXX methods.
  17 //
  18 // Because BaseDropTarget is ref counted you shouldn't delete it directly,
  19 // rather wrap it in a scoped_refptr. Be sure and invoke RevokeDragDrop(m_hWnd)
  20 // before the HWND is deleted too.
  21 //
  22 // This class is meant to be used in a STA and is not multithread-safe.
  23 class BaseDropTarget : public IDropTarget {
  24  public:
  25   // Create a new BaseDropTarget associating it with the given HWND.
  26   explicit BaseDropTarget(HWND hwnd);
  27   virtual ~BaseDropTarget();
  28
  29   // When suspend is set to |true|, the drop target does not receive drops from
  30   // drags initiated within the owning HWND.
  31   // TODO(beng): (http://b/1085385) figure out how we will handle legitimate
  32   //             drag-drop operations within the same HWND, such as dragging
  33   //             selected text to an edit field.
  34   void set_suspend(bool suspend) { suspend_ = suspend; }
  35
  36   // IDropTarget implementation:
  37   HRESULT __stdcall DragEnter(IDataObject* data_object,
  38                               DWORD key_state,
  39                               POINTL cursor_position,
  40                               DWORD* effect);
  41   HRESULT __stdcall DragOver(DWORD key_state,
  42                              POINTL cursor_position,
  43                              DWORD* effect);
  44   HRESULT __stdcall DragLeave();
  45   HRESULT __stdcall Drop(IDataObject* data_object,
  46                          DWORD key_state,
  47                          POINTL cursor_position,
  48                          DWORD* effect);
  49
  50   // IUnknown implementation:
  51   HRESULT __stdcall QueryInterface(const IID& iid, void** object);
  52   ULONG __stdcall AddRef();
  53   ULONG __stdcall Release();
  54
  55  protected:
  56   // Returns the hosting HWND.
  57   HWND GetHWND() { return hwnd_; }
  58
  59   // Invoked when the cursor first moves over the hwnd during a dnd session.
  60   // This should return a bitmask of the supported drop operations:
  61   // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
  62   // DROPEFFECT_MOVE.
  63   virtual DWORD OnDragEnter(IDataObject* data_object,
  64                             DWORD key_state,
  65                             POINT cursor_position,
  66                             DWORD effect);
  67
  68   // Invoked when the cursor moves over the window during a dnd session.
  69   // This should return a bitmask of the supported drop operations:
  70   // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
  71   // DROPEFFECT_MOVE.
  72   virtual DWORD OnDragOver(IDataObject* data_object,
  73                            DWORD key_state,
  74                            POINT cursor_position,
  75                            DWORD effect);
  76
  77   // Invoked when the cursor moves outside the bounds of the hwnd during a
  78   // dnd session.
  79   virtual void OnDragLeave(IDataObject* data_object);
  80
  81   // Invoked when the drop ends on the window. This should return the operation
  82   // that was taken.
  83   virtual DWORD OnDrop(IDataObject* data_object,
  84                        DWORD key_state,
  85                        POINT cursor_position,
  86                        DWORD effect);
  87
  88  private:
  89   // Returns the cached drop helper, creating one if necessary. The returned
  90   // object is not addrefed. May return NULL if the object couldn't be created.
  91   static IDropTargetHelper* DropHelper();
  92
  93   // The data object currently being dragged over this drop target.
  94   scoped_refptr<IDataObject> current_data_object_;
  95
  96   // A helper object that is used to provide drag image support while the mouse
  97   // is dragging over the content area.
  98   //
  99   // DO NOT ACCESS DIRECTLY! Use DropHelper() instead, which will lazily create
 100   // this if it doesn't exist yet. This object can take tens of milliseconds to
 101   // create, and we don't want to block any window opening for this, especially
 102   // since often, DnD will never be used. Instead, we force this penalty to the
 103   // first time it is actually used.
 104   static IDropTargetHelper* cached_drop_target_helper_;
 105
 106   // The HWND of the source. This HWND is used to determine coordinates for
 107   // mouse events that are sent to the renderer notifying various drag states.
 108   HWND hwnd_;
 109
 110   // Whether or not we are currently processing drag notifications for drags
 111   // initiated in this window.
 112   bool suspend_;
 113
 114   LONG ref_count_;
 115
 116   DISALLOW_EVIL_CONSTRUCTORS(BaseDropTarget);
 117 };
 118
 119 #endif  // BASE_BASE_DROP_TARGET_H_