{"id":8763,"date":"2011-12-30T07:00:00","date_gmt":"2011-12-30T07:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2011\/12\/30\/using-the-mns_dragdrop-style-menu-rearrangement\/"},"modified":"2011-12-30T07:00:00","modified_gmt":"2011-12-30T07:00:00","slug":"using-the-mns_dragdrop-style-menu-rearrangement","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20111230-00\/?p=8763","title":{"rendered":"Using the MNS_DRAGDROP style: Menu rearrangement"},"content":{"rendered":"

\nIn order to do drag-drop rearrangement of menus,\nyou need four things, most of which we already know how to do.\n<\/p>\n

    \n
  1. Dragging an item out of a menu.\n \n Check<\/a>.<\/p>\n
  2. Dropping an item into a menu.\n \n Check<\/a>.<\/p>\n
  3. Connecting the drag with the drop.\n
  4. Rearranging menu items in response to the operation.\n<\/ol>\n

    \nLet’s do step 4 first, just to mix things up.\nAnd since this is just a demonstration rather than production code,\nI’m only going to support string menu items of up to 255 characters\nin length.\n<\/p>\n

    \nBOOL MoveMenuItem(HMENU hmenu, UINT uPosFrom, UINT uPosInsertAfter)\n{\n BOOL fRc = FALSE;\n TCHAR sz[256];\n if (GetMenuString(hmenu, uPosFrom, sz, 256, MF_BYPOSITION) &&\n     InsertMenu(hmenu, uPosInsertAfter, MF_BYPOSITION,\n                GetMenuItemID(hmenu, uPosFrom), sz)) {\n  if (uPosFrom > uPosInsertAfter) uPosFrom++;\n  fRc = DeleteMenu(hmenu, uPosFrom, MF_BYPOSITION);\n }\n return fRc;\n}\n<\/pre>\n
    \nOne thing you might not have noticed is that I inserted the\ncopy before deleting the original.\nThat way, we don’t get stuck in the situation where we deleted\nthe original, then the reinsertion fails, and now we’ve lost the\nmenu item.\n(We can still get stuck if the deletion of the original fails,\nbut the hope is that that is much more unlikely than the failure\nof an insertion.)\n<\/p>\n
    \nOkay, the next part is connecting the drag with the drop.\nTo do that, I’ll need some helper COM objects.\nBut first, I’m going to introduce something that I should have\nintroduced earlier: Objects that do nothing!\n(Just like our scratch program, they start out doing nothing,\nand then we’ll modify them to do something.)\n<\/p>\n
    \n\/\/ dummy data object\nclass CEmptyDataObject : public IDataObject\n{\npublic:\n  \/\/ IUnknown\n  STDMETHODIMP QueryInterface(REFIID riid, void **ppvObj)\n  {\n    IUnknown *punk = NULL;\n    if (riid == IID_IUnknown) {\n      punk = static_cast<IUnknown*>(this);\n    } else if (riid == IID_IDataObject) {\n      punk = static_cast<IDataObject*>(this);\n    }\n    *ppvObj = punk;\n    if (punk) {\n      punk->AddRef();\n      return S_OK;\n    } else {\n      return E_NOINTERFACE;\n    }\n  }\n  STDMETHODIMP_(ULONG) AddRef()\n  {\n    return ++m_cRef;\n  }\n  STDMETHODIMP_(ULONG) Release()\n  {\n    ULONG cRef = --m_cRef;\n    if (cRef == 0) delete this;\n    return cRef;\n  }\n  \/\/ IDataObject\n  STDMETHODIMP GetData(FORMATETC *pfe, STGMEDIUM *pmed)\n  {\n    ZeroMemory(pmed, sizeof(*pmed));\n    return DV_E_FORMATETC;\n  }\n  STDMETHODIMP GetDataHere(FORMATETC *pfe, STGMEDIUM *pmed)\n  {\n    return E_NOTIMPL;\n  }\n  STDMETHODIMP QueryGetData(FORMATETC *pfe)\n  {\n    return DV_E_FORMATETC;\n  }\n  STDMETHODIMP GetCanonicalFormatEtc(FORMATETC *pfeIn,\n                                     FORMATETC *pfeOut)\n  {\n    *pfeOut = *pfeIn;\n    pfeOut->ptd = NULL;\n    return DATA_S_SAMEFORMATETC;\n  }\n  STDMETHODIMP SetData(FORMATETC *pfe, STGMEDIUM *pmed,\n                       BOOL fRelease)\n  {\n    return E_NOTIMPL;\n  }\n  STDMETHODIMP EnumFormatEtc(DWORD dwDirection,\n                             LPENUMFORMATETC *ppefe)\n  {\n  *ppefe = NULL;\n  return E_NOTIMPL;\n  }\n  STDMETHODIMP DAdvise(FORMATETC *pfe, DWORD grfAdv,\n                    IAdviseSink *pAdvSink, DWORD *pdwConnection)\n  {\n    *pdwConnection = 0;\n    return OLE_E_ADVISENOTSUPPORTED;\n  }\n  STDMETHODIMP DUnadvise(DWORD dwConnection)\n  {\n    return OLE_E_ADVISENOTSUPPORTED;\n  }\n  STDMETHODIMP EnumDAdvise(LPENUMSTATDATA *ppefe)\n  {\n    *ppefe = NULL;\n    return OLE_E_ADVISENOTSUPPORTED;\n  }\n  CEmptyDataObject() : m_cRef(1) { }\n  virtual ~CEmptyDataObject() { }\nprivate:\n  ULONG m_cRef;\n};\n<\/pre>\n
    \nThe CEmpty­Data­Object<\/code>\nis simply a data object that contains no data.\nAnd here’s an equally uninteresting\nCEmpty­Drop­Target<\/code>:\n<\/p>\n
    \nclass CEmptyDropTarget : public IDropTarget\n{\npublic:\n  \/\/ IUnknown\n  STDMETHODIMP QueryInterface(REFIID riid, void **ppvObj)\n  {\n    IUnknown *punk = NULL;\n    if (riid == IID_IUnknown) {\n      punk = static_cast<IUnknown*>(this);\n    } else if (riid == IID_IDropTarget) {\n      punk = static_cast<IDropTarget*>(this);\n    }\n    *ppvObj = punk;\n    if (punk) {\n      punk->AddRef();\n      return S_OK;\n    } else {\n      return E_NOINTERFACE;\n    }\n  }\n  STDMETHODIMP_(ULONG) AddRef()\n  {\n    return ++m_cRef;\n  }\n  STDMETHODIMP_(ULONG) Release()\n  {\n    ULONG cRef = --m_cRef;\n    if (cRef == 0) delete this;\n    return cRef;\n  }\n  \/\/ IDropTarget\n  STDMETHODIMP DragEnter(IDataObject *pdto, DWORD grfKeyState,\n                         POINTL pt, DWORD *pdwEffect)\n  {\n    *pdwEffect = DROPEFFECT_NONE;\n    return E_NOTIMPL;\n  }\n  STDMETHODIMP DragOver(DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)\n  {\n    *pdwEffect = DROPEFFECT_NONE;\n    return E_NOTIMPL;\n  }\n  STDMETHODIMP DragLeave()\n  {\n    return E_NOTIMPL;\n  }\n  STDMETHODIMP Drop(IDataObject *pdto, DWORD grfKeyState,\n                    POINTL pt, DWORD *pdwEffect)\n  {\n    *pdwEffect = DROPEFFECT_NONE;\n    return E_NOTIMPL;\n  }\n  CEmptyDropTarget() : m_cRef(1) { }\n  virtual ~CEmptyDropTarget() { }\nprivate:\n  ULONG m_cRef;\n};\n<\/pre>\n
    \nOkay, now back to item 3: Connecting the drag with the drop.\nYour initial reaction might be to create a new clipboard format\ncalled, say, Dragged­Menu­Item<\/tt>\nwhich takes the form of a TYMED_HGLOBAL<\/code>\nconsisting of a struct like\n<\/p>\n
    \nstruct MENUANDITEM\n{\n HMENU hmenu;\n UINT uItem;\n};\n<\/pre>\n
    \nBut once you do that, you already have a problem:\nWhat happens if this item is dragged out of a 32-bit process\nand dropped into a 64-bit process?\nThe size of HMENU<\/code> is different between the two processes,\nso the 32-bit and 64-bit\nMENU­AND­ITEM<\/code> structures are\nnot compatible.\nThis is an example of\nhow you need to be aware of inter-process\ncommunications scenarios when developing persistence formats.\nIn this case,\n\nwe are passing a pointer-sized object between processes<\/a>.\nAlthough most people think of a persistence format as a file format,\nhere’s a case where a persistence format takes the form of\nan in-memory storage format.\n<\/p>\n
    \nYou might decide to solve this problem by tweaking the structure\nto accommodate 32-bit and 64-bit Windows:\n<\/p>\n
    \nstruct MENUANDITEM\n{\n __int64 i64Menu;\n UINT uItem;\n void SetMenu(HMENU hmenu) { i64Menu = (INT_PTR)hmenu; }\n HMENU GetMenu() const { return (HMENU)(INT_PTR)i64Menu; }\n};\n<\/pre>\n
    \nBut there’s an easier way out:\nSince we only want to support drag\/drop menu editing from within\nthe same menu (we don’t care about dragging an item from one\nmenu to another menu),\nthe drag source and drop target reside in the same process,\nso all we need to do is verify the data object’s identity,\nand if it’s our data object, we can consult side data to determine\nwhat is being dragged.\n<\/p>\n
    \nOkay, so let’s start with a fresh\n\nscratch program<\/a>,\nand paste in the following:\n<\/p>\n