Question

I’m working on a drag and drop problem now and trying to get the PIDLs of the items being dragged from windows shell to my application.

The code below can get correct PIDLs if the dragged item is ‘My Computer’ or ‘Control Panel’ itself, but it doesn’t work when the dragged item is an item in the ‘Control Panel’.

What’s wrong with my code?

---

#define GetPIDLFolder(pida) (LPCITEMIDLIST)(((LPBYTE)pida)+(pida)->aoffset[0])
#define GetPIDLItem(pida, i) (LPCITEMIDLIST)(((LPBYTE)pida)+(pida)->aoffset[i+1])

STGMEDIUM medium;

UINT fmt = RegisterClipboardFormat(CFSTR_SHELLIDLIST);
FORMATETC fe= {fmt, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL};
HRESULT GETDATA_RESULT = pDataObject->GetData(&fe, &medium);

if (SUCCEEDED(GETDATA_RESULT))
{
    LPIDA pida = (LPIDA)GlobalLock(medium.hGlobal);
    LPCITEMIDLIST pidlFolder = GetPIDLFolder(pida);

    int n = pida->cidl;  // the n is always correct
    if( n > 0 )
    {
        LPCITEMIDLIST pidlItem = GetPIDLItem(pida, 0);
        // the pidlItem is wrong when the dragged object is an item in 'Control Panel'
    }

    GlobalUnlock(medium.hGlobal);
}
ReleaseStgMedium(&medium);

---

Any idea? Thanks

Zach@Shine

Answer 1

If I D&D Mouse, Network Connections and Fonts I get the following output in my test app:

• 0 Mouse | sfgao=4 hr=0
• 1 ::{20D04FE0-3AEA-1069-A2D8-08002B30309D}\::{21EC2020-3AEA-1069-A2DD-08002B30309D}\::{7007ACC7-3202-11D1-AAD2-00805FC1270E} | sfgao=20000004 hr=0
• 2 C:\WINDOWS\Fonts | sfgao=60000004 hr=0

The Network Connections and Fonts pidls can be converted to fully qualified shell paths while Mouse only returns a relative path/displayname.
This makes sense if you check the documentation for IShellFolder::GetDisplayNameOf:

…They do not guarantee that
IShellFolder will return the requested
form of the name. If that form is not
available, a different one might be
returned. In particular, there is no
guarantee that the name returned by
the SHGDN_FORPARSING flag will be
successfully parsed by
IShellFolder::ParseDisplayName. There
are also some combinations of flags
that might cause the
GetDisplayNameOf/ParseDisplayName
round trip to not return the original
identifier list. This occurrence is
exceptional, but you should check to
be sure.

It is clear that when dealing with controlpanel items, you need to keep the pidl around and only use GetDisplayNameOf for display strings in your UI.
(IShellLink::SetIDList on the Mouse pidl will create a working shortcut so the pidl is valid)

void OnDrop(IDataObject*pDO) 
{
    STGMEDIUM medium;
    UINT fmt = RegisterClipboardFormat(CFSTR_SHELLIDLIST);
    FORMATETC fe= {fmt, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL};
    HRESULT hr = pDO->GetData(&fe, &medium);
    if (SUCCEEDED(hr)) 
    {
        LPIDA pida = (LPIDA)GlobalLock(medium.hGlobal);
        if (pida) 
        {
            LPCITEMIDLIST pidlFolder = GetPIDLFolder(pida);
            for (UINT i=0; i<pida->cidl; ++i) 
            {
                LPCITEMIDLIST pidlItem = GetPIDLItem(pida,i);
                LPITEMIDLIST pidlAbsolute = ILCombine(pidlFolder,pidlItem);
                if (pidlAbsolute) 
                {
                    IShellFolder*pParentSF;
                    hr= SHBindToParent(pidlAbsolute,IID_IShellFolder,(void**)&pParentSF,&pidlItem);
                    if (SUCCEEDED(hr))
                    {
                        STRRET str; 
                        hr= pParentSF->GetDisplayNameOf(pidlItem, SHGDN_FORPARSING, &str);
                        if (SUCCEEDED(hr))
                        {
                            TCHAR szName[MAX_PATH];
                            hr= StrRetToBuf(&str,pidlItem,szName,MAX_PATH);
                            if (SUCCEEDED(hr)) 
                            {
                                SFGAOF sfgao = SFGAO_FOLDER|SFGAO_FILESYSTEM|SFGAO_HASSUBFOLDER|SFGAO_CANLINK;
                                hr= pParentSF->GetAttributesOf(1,&pidlItem,&sfgao);
                                TRACE(_T("%u %s | sfgao=%X hr=%X\n"),i,szName,sfgao,hr);
                                CreateTestShortcut(pidlAbsolute);
                            }
                        }
                        pParentSF->Release();
                    }
                    ILFree(pidlAbsolute);
                }
            }
            GlobalUnlock(medium.hGlobal);
        }
        ReleaseStgMedium(&medium);
    }
}