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

, 20 Nov 2002
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Uses the poorly documented SHChangeNotifyRegister function to receive notification upon shell events.

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

You will need the following includes and definition:
#include <shlobj.h>
#define WM_USER_MEDIACHANGED WM_USER+88
Together with a member variable to release the request later:
ULONG m_ulSHChangeNotifyRegister;
Nullify the member variable in your constructor, then register to be notified by the shell (perhaps in OnInitDialog for example):
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
}
Add a message handler to your message map for the notification message:
ON_MESSAGE(WM_USER_MEDIACHANGED, OnMediaChanged)
Together with the corresponding declaration:
afx_msg LRESULT OnMediaChanged(WPARAM, LPARAM);
Then deal with the message as desired:
// 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;
}
Finally deregister your request when no longer required:
void CMyWnd::OnDestroy() 
{
    if(m_ulSHChangeNotifyRegister)
        VERIFY(SHChangeNotifyDeregister(m_ulSHChangeNotifyRegister));

    CWnd::OnDestroy();    
}

References

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Obliterator
Software Developer
United Kingdom United Kingdom
No Biography provided

Comments and Discussions

 
QuestionCould you give me a full demo source? PinmemberVioletPirate18-Oct-11 23:54 
GeneralSame message received twice Pinmembernanfang24-May-08 9:57 
GeneralTo check whether any USB device is connected PinmemberMember #384610121-Feb-07 3:16 
GeneralRe: To check whether any USB device is connected Pinmemberbzucko1-Mar-07 23:54 
GeneralConsole App PinmemberBeng Heng22-Mar-05 21:53 
GeneralRe: Console App Pinmemberpada445-Apr-06 12:28 
QuestionNo notification messages for floppy inserted or removed? PinmemberMicheal Huang14-Dec-04 22:19 
AnswerRe: No notification messages for floppy inserted or removed? PinmemberObliterator15-Dec-04 0:16 
GeneralRe: No notification messages for floppy inserted or removed? PinmemberThatsAlok22-Feb-05 19:08 
GeneralWhen app not running Pinmemberbryce2-Jun-04 20:59 
GeneralRe: When app not running PinmemberObliterator3-Jun-04 1:12 
GeneralRe: When app not running Pinmemberbryce3-Jun-04 2:08 
GeneralLinker error PinmemberOyvind10-May-04 20:04 
GeneralRe: Linker error PinmemberObliterator11-May-04 4:24 
Generalthis doesn't compile PinsussAnonymous23-Apr-04 18:05 
GeneralRe: this doesn't compile PinmemberHakanErd25-Apr-04 10:15 
GeneralExcept when Autorun is off PinmemberMrLeeGriffiths15-May-03 23:43 
Generalsome remarks Pinmemberumeca7427-Nov-02 0:57 
GeneralRe: some remarks PinmemberObliterator27-Nov-02 4:29 
GeneralRe: some remarks Pinmemberumeca7428-Nov-02 0:24 
GeneralI cannot compile this PinmemberAlex F24-Nov-02 20:17 
GeneralThe same with SP3 PinmemberAlex F24-Nov-02 21:51 
GeneralRe: The same with SP3 PinmemberObliterator25-Nov-02 2:57 
Generalfor reference (slightly off topic) Pinmembermgama21-Nov-02 7:19 
GeneralRe: for reference (slightly off topic) PinmemberObliterator21-Nov-02 15:09 
GeneralRe: for reference (slightly off topic) PinsussAnonymous3-Jun-04 2:11 
GeneralRe: for reference (slightly off topic) PinmemberObliterator3-Jun-04 3:07 
GeneralNice! PinmemberRavi Bhavnani21-Nov-02 7:01 
GeneralWin2K minimum PinmemberThomas Freudenberg21-Nov-02 5:24 
GeneralRe: Win2K minimum PinmemberKwakkie21-Nov-02 5:38 
GeneralRe: Win2K minimum PinmemberThomas Freudenberg21-Nov-02 5:54 
GeneralRe: Win2K minimum PinmemberKwakkie21-Nov-02 6:03 
GeneralRe: Win2K minimum PinmemberObliterator21-Nov-02 15:13 
GeneralRe: Win2K minimum PinsussAnonymous16-Feb-03 18:04 
GeneralRe: Win2K minimum PinmemberNorthernRail14-Dec-04 5:41 
GeneralRe: Win2K minimum PinmemberObliterator14-Dec-04 7:09 

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