Using the shell to receive notification of removable media being inserted or removed.

Introduction

Recently I needed to determine when removable media, such as a zip disk or media card, had been inserted by the user.

I initially looked into the WM_DEVICECHANGE broadcast message only to realise this supports CDROMs and little else. Fortunately there is another way via the shell, through the scarcely documented SHChangeNotifyRegister function.

We can register to be informed by the shell when certain events of interest occur. The events are numerous - covering when a drive is added or removed, files are renamed, etc. However of particular interest here are the notifications for media being inserted or removed.

Its scarcely rocket science but piecing the various bits of information together to utilise this functionality took far longer than it should. I was amazed there was no article here on CP covering this, so figured I should rectify that!

Implementation

#include <shlobj.h>
#define WM_USER_MEDIACHANGED WM_USER+88

ULONG m_ulSHChangeNotifyRegister;

CMyWnd::CMyWnd()
{
    ulSHChangeNotifyRegister = NULL;
}

BOOL CMyWnd::OnInitDialog() 
{
    CWnd::OnInitDialog();

    // Request notification from shell of media insertion -
    // allows us to detect removable media or a multimedia card
    HWND hWnd = GetSafeHwnd();
    LPITEMIDLIST ppidl;
    if(SHGetSpecialFolderLocation(hWnd, CSIDL_DESKTOP, &ppidl) == NOERROR)
    {
        SHChangeNotifyEntry shCNE;
        shCNE.pidl = ppidl;
        shCNE.fRecursive = TRUE;

        // Returns a positive integer registration identifier (ID).
        // Returns zero if out of memory or in response to invalid parameters.
        m_ulSHChangeNotifyRegister = SHChangeNotifyRegister(hWnd,  <BR>                                          // Hwnd to receive notification
                SHCNE_DISKEVENTS,                          <BR>                                          // Event types of interest (sources)
                SHCNE_MEDIAINSERTED|SHCNE_MEDIAREMOVED,    <BR>                                          // Events of interest - use <BR>                                          // SHCNE_ALLEVENTS for all events
                WM_USER_MEDIACHANGED,     <BR>                                          // Notification message to be sent <BR>                                          // upon the event
                1,                         <BR>                                          // Number of entries in the pfsne array
                &shCNE);  // Array of SHChangeNotifyEntry structures that <BR>                          // contain the notifications. This array should <BR>                          // always be set to one when calling SHChnageNotifyRegister
                          // or SHChangeNotifyDeregister will not work properly.
    
        ASSERT(m_ulSHChangeNotifyRegister != 0);    // Shell notification failed
    }
    else
        ASSERT(FALSE);    // Failed to get desktop location
}

ON_MESSAGE(WM_USER_MEDIACHANGED, OnMediaChanged)

afx_msg LRESULT OnMediaChanged(WPARAM, LPARAM);

// The lParam value contains the event SHCNE_xxxx
// The wParam value supplies the SHNOTIFYSTRUCT

typedef struct {
    DWORD dwItem1;    // dwItem1 contains the previous PIDL or name of the folder. 
    DWORD dwItem2;    // dwItem2 contains the new PIDL or name of the folder. 
} SHNOTIFYSTRUCT;

LRESULT CMyWnd::OnMediaChanged(WPARAM wParam, LPARAM lParam)
{
    SHNOTIFYSTRUCT *shns = (SHNOTIFYSTRUCT *)wParam;
    CString strPath, strMsg;

    switch(lParam)
    {
        case SHCNE_MEDIAINSERTED:        // media inserted event
        {
            strPath = GetPathFromPIDL(shns->dwItem1);
            if(!strPath.IsEmpty())
            {
                // Process strPath as required, for now a simple message box
                strMsg.Format("Media inserted into %s", strPath);
                AfxMessageBox(strMsg);
            }
        }
        case SHCNE_MEDIAREMOVED:        // media removed event
        {
            strPath = GetPathFromPIDL(shns->dwItem1);
            if(!strPath.IsEmpty())
            {
                // Process strPath as required, for now a simple message box
                strMsg.Format("Media removed from %s", strPath);
                AfxMessageBox(strMsg);
            }
        }
        //case SHCNE_xxxx:  Add other events processing here
    }
    return NULL;
}

CString CMyWnd::GetPathFromPIDL(DWORD pidl)
{
    char sPath[MAX_PATH];
    CString strTemp = _T("");
    if(SHGetPathFromIDList((struct _ITEMIDLIST *)pidl, sPath))
        strTemp = sPath;
    
    return strTemp;
}

void CMyWnd::OnDestroy() 
{
    if(m_ulSHChangeNotifyRegister)
        VERIFY(SHChangeNotifyDeregister(m_ulSHChangeNotifyRegister));

    CWnd::OnDestroy();    
}

References

• MSDN: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/shell/reference/Functions/SHChangeNotifyRegister.asp[^]
• Sameer Maggon: http://pcquest.ciol.com/content/coding/102070301.asp[^]

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