A File Checksum Shell Menu Extension DLL

// MenuItem.cpp : Implementation of CMenuItem
#include "stdafx.h"
#include "CtxTest.h"
#include "MenuItem.h"

#include <string>
#include <assert.h>

/////////////////////////////////////////////////////////////////////////////
// CMenuItem
HRESULT CMenuItem::InvokeCommand ( LPCMINVOKECOMMANDINFO pCmdInfo )
{
    // If lpVerb really points to a std::string,
    //   ignore this function call and bail out.
    if ( 0 != HIWORD( pCmdInfo->lpVerb ) ) { return E_INVALIDARG; }

    // Get the command index - the only valid one is 0.
    switch( LOWORD( pCmdInfo->lpVerb ) )
    {
        case 0:
        {

            MessageBox( pCmdInfo->hwnd, file.c_str(),
                      _T("Context Menu Test"), MB_ICONINFORMATION );       

            return S_OK;
            break;
        }
     
        default:
            assert( false );           
            break;
    }

    return E_INVALIDARG;
}

HRESULT CMenuItem::GetCommandString( UINT idCmd, UINT uFlags,
                     UINT* pwReserved, LPSTR pszName, UINT cchMax )
{

    pwReserved;         // Warning C4100 suppression

    // Check idCmd, it must be 0 since we have only one menu item.
    if ( 0 != idCmd ) { return E_INVALIDARG; }
 
    // If Explorer is asking for a help std::string, copy our std::string
    //   into the supplied buffer.
    if( uFlags & GCS_HELPTEXT )
    {        
        if ( uFlags & GCS_UNICODE )
        {
            LPWSTR szText = L"Context Menu Test Description";
            // We need to cast pszName to a Unicode std::string, and then use the
            // Unicode std::string copy API.
            lstrcpynW ( reinterpret_cast<LPWSTR>( pszName ), szText, cchMax );
        }
        else
        {
            LPSTR szText = "Context Menu Test Description";
            // Use the ANSI std::string copy API to return the help std::string.
            lstrcpynA ( pszName, szText, cchMax );
        }

        return S_OK;
    }

    return E_INVALIDARG;
}

HRESULT CMenuItem::QueryContextMenu( HMENU hmenu, UINT uMenuIndex,
                       UINT uidFirstCmd, UINT uidLastCmd, UINT uFlags )
{   
    uidFirstCmd;        // Suppression Warning C4100
    uidLastCmd;         // Suppression Warning C4100

    // If the flags include CMF_DEFAULTONLY then we shouldn't do anything.
    if( uFlags & CMF_DEFAULTONLY )
        { return MAKE_HRESULT ( SEVERITY_SUCCESS, FACILITY_NULL, 0 ); }

    InsertMenu( hmenu, uMenuIndex, MF_BYPOSITION,
                uidFirstCmd, _T("Context Menu Test") );

    return MAKE_HRESULT( SEVERITY_SUCCESS, FACILITY_NULL, 1 );
}

STDMETHODIMP CMenuItem::Initialize( LPCITEMIDLIST pidlFolder,
                                      LPDATAOBJECT pDataObj, HKEY hProgID )
{
    pidlFolder;     // Warning C4100 suppression
    hProgID;        // Warning C4100 suppression

    FORMATETC fmt = { CF_HDROP, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
    STGMEDIUM stg = { TYMED_HGLOBAL };
    HDROP     hDrop;

    // Look for CF_HDROP data in the data object. If there
    // is no such data, return an error back to Explorer.
    if( FAILED( pDataObj->GetData ( &fmt, &stg ) ))
        { return E_INVALIDARG; }

    // Get a pointer to the actual data.
    hDrop = static_cast<HDROP>( GlobalLock ( stg.hGlobal ) );

    // Make sure it worked.
    if( NULL == hDrop )
        { return E_INVALIDARG; }

    // Sanity check - make sure there is at least one filename.
    UINT uNumFiles = DragQueryFile( hDrop, static_cast<UINT>(-1), NULL, 0 );    
    if( 0 == uNumFiles )
    {
        GlobalUnlock ( stg.hGlobal );
        ReleaseStgMedium ( &stg );

        return E_INVALIDARG;
    }

    HRESULT hr = S_OK;

    // The author has encountered situations where
    //   MAX_PATH*2 was a bit too small...
    TCHAR szFile[ MAX_PATH * 4 + 1 ];

    DragQueryFile( static_cast<HDROP>( stg.hGlobal ),
                   0 /*first file*/, szFile, MAX_PATH * 4 );

    file = szFile;

    GlobalUnlock ( stg.hGlobal );
    ReleaseStgMedium ( &stg );

    return hr;
}