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 suspended is set to |true|, the drop target does not receive drops
  30   // from 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   bool suspended() const { return suspended_; }
  35   void set_suspended(bool suspended) { suspended_ = suspended; }
  36
  37   // IDropTarget implementation:
  38   HRESULT __stdcall DragEnter(IDataObject* data_object,
  39                               DWORD key_state,
  40                               POINTL cursor_position,
  41                               DWORD* effect);
  42   HRESULT __stdcall DragOver(DWORD key_state,
  43                              POINTL cursor_position,
  44                              DWORD* effect);
  45   HRESULT __stdcall DragLeave();
  46   HRESULT __stdcall Drop(IDataObject* data_object,
  47                          DWORD key_state,
  48                          POINTL cursor_position,
  49                          DWORD* effect);
  50
  51   // IUnknown implementation:
  52   HRESULT __stdcall QueryInterface(const IID& iid, void** object);
  53   ULONG __stdcall AddRef();
  54   ULONG __stdcall Release();
  55
  56  protected:
  57   // Returns the hosting HWND.
  58   HWND GetHWND() { return hwnd_; }
  59
  60   // Invoked when the cursor first moves over the hwnd during a dnd session.
  61   // This should return a bitmask of the supported drop operations:
  62   // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
  63   // DROPEFFECT_MOVE.
  64   virtual DWORD OnDragEnter(IDataObject* data_object,
  65                             DWORD key_state,
  66                             POINT cursor_position,
  67                             DWORD effect);
  68
  69   // Invoked when the cursor moves over the window during a dnd session.
  70   // This should return a bitmask of the supported drop operations:
  71   // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
  72   // DROPEFFECT_MOVE.
  73   virtual DWORD OnDragOver(IDataObject* data_object,
  74                            DWORD key_state,
  75                            POINT cursor_position,
  76                            DWORD effect);
  77
  78   // Invoked when the cursor moves outside the bounds of the hwnd during a
  79   // dnd session.
  80   virtual void OnDragLeave(IDataObject* data_object);
  81
  82   // Invoked when the drop ends on the window. This should return the operation
  83   // that was taken.
  84   virtual DWORD OnDrop(IDataObject* data_object,
  85                        DWORD key_state,
  86                        POINT cursor_position,
  87                        DWORD effect);
  88
  89   // Return the drag identity.
  90   static int32 GetDragIdentity() { return drag_identity_; }
  91
  92  private:
  93   // Returns the cached drop helper, creating one if necessary. The returned
  94   // object is not addrefed. May return NULL if the object couldn't be created.
  95   static IDropTargetHelper* DropHelper();
  96
  97   // The data object currently being dragged over this drop target.
  98   scoped_refptr<IDataObject> current_data_object_;
  99
 100   // A helper object that is used to provide drag image support while the mouse
 101   // is dragging over the content area.
 102   //
 103   // DO NOT ACCESS DIRECTLY! Use DropHelper() instead, which will lazily create
 104   // this if it doesn't exist yet. This object can take tens of milliseconds to
 105   // create, and we don't want to block any window opening for this, especially
 106   // since often, DnD will never be used. Instead, we force this penalty to the
 107   // first time it is actually used.
 108   static IDropTargetHelper* cached_drop_target_helper_;
 109
 110   // The drag identity (id). An up-counter that increases when the cursor first
 111   // moves over the HWND in a DnD session (OnDragEnter). 0 is reserved to mean
 112   // the "no/unknown" identity, and is used for initialization. The identity is
 113   // sent to the renderer in drag enter notifications. Note: the identity value
 114   // is passed over the renderer NPAPI interface to gears, so use int32 instead
 115   // of int here.
 116   static int32 drag_identity_;
 117
 118   // The HWND of the source. This HWND is used to determine coordinates for
 119   // mouse events that are sent to the renderer notifying various drag states.
 120   HWND hwnd_;
 121
 122   // Whether or not we are currently processing drag notifications for drags
 123   // initiated in this window.
 124   bool suspended_;
 125
 126   LONG ref_count_;
 127
 128   DISALLOW_EVIL_CONSTRUCTORS(BaseDropTarget);
 129 };
 130
 131 #endif  // BASE_BASE_DROP_TARGET_H_