How can I use RegisterDeviceNotification without a window handle?

Question

I'm writing a DLL library that interfaces to a USB device using winusb in VB.NET.

Since it's a DLL, I have no window, and it's possible that users of my library will also not have a window (command line apps, for instance).

The examples I've seen that detect device attach and detach all use RegisterDeviceNotification which requires a window handle to receive the attach/detach messages at.

How do I receive these messages directly into a function without a window to get a handle from?

Answer 1

I recently found a solution that seems more elegant than RegisterDeviceNotification for an application without a GUI.

    void onEventArrived(object sender, EventArrivedEventArgs e)
    {
        ManagementBaseObject _o = e.NewEvent["TargetInstance"] as ManagementBaseObject;

        if (_o != null)
        {
            using (ManagementObject mo = new ManagementObject(_o["Dependent"].ToString()))
            {
                if (mo != null)
                {
                    try
                    {
                        if (mo.GetPropertyValue("DeviceID").ToString() != string.Empty)
                        {
                            //connected
                        }
                    }

                    catch (ManagementException ex)
                    {
                        //disconnected
                    }
                }
            }
        }
    }

Initialize this code by calling

        System.Management.WqlEventQuery _q = new WqlEventQuery("__InstanceOperationEvent", "TargetInstance ISA 'Win32_USBControllerDevice' ");
        _q.WithinInterval = TimeSpan.FromSeconds(1);
        ManagementEventWatcher _w = new ManagementEventWatcher(_q);
        _w.EventArrived += new EventArrivedEventHandler(onEventArrived);
        _w.Start();

Also make sure to add a reference to System.Management

Answer 2

While this isn't for .NET, it provides a template in C++ for the process of creating the structures necessary to handle the window callbacks, and provides a way to register a custom window handle without having a real window:

http://msdn.microsoft.com/en-us/library/aa363432%28VS.85%29.aspx

This example uses a window handle for device change notifications and contains a large amount of code to support the windowing mechanisms. An application intended to be installed as a Windows service would contain different support code.

The application will receive the WM_DEVICECHANGE message whenever a USB device interface event notification is sent.

The system broadcasts a set of default device change events to all applications and services. You do not need to register to receive these default events. For details, see the Remarks section in RegisterDeviceNotification.

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <strsafe.h>
#include <dbt.h>

// This GUID is for all USB serial host PnP drivers, but you can replace it 
// with any valid device class guid.
GUID WceusbshGUID = { 0x25dbce51, 0x6c8f, 0x4a72, 
                      0x8a,0x6d,0xb5,0x4c,0x2b,0x4f,0xc8,0x35 };

// For informational messages and window titles
PWSTR g_pszAppName;

// Forward declarations
void OutputMessage(HWND hOutWnd, WPARAM wParam, LPARAM lParam);
void ErrorHandler(LPTSTR lpszFunction);

//
// DoRegisterDeviceInterfaceToHwnd
//
BOOL DoRegisterDeviceInterfaceToHwnd( 
    IN GUID InterfaceClassGuid, 
    IN HWND hWnd,
    OUT HDEVNOTIFY *hDeviceNotify 
)
// Routine Description:
//     Registers an HWND for notification of changes in the device interfaces
//     for the specified interface class GUID. 

// Parameters:
//     InterfaceClassGuid - The interface class GUID for the device 
//         interfaces. 

//     hWnd - Window handle to receive notifications.

//     hDeviceNotify - Receives the device notification handle. On failure, 
//         this value is NULL.

// Return Value:
//     If the function succeeds, the return value is TRUE.
//     If the function fails, the return value is FALSE.

// Note:
//     RegisterDeviceNotification also allows a service handle be used,
//     so a similar wrapper function to this one supporting that scenario
//     could be made from this template.
{
    DEV_BROADCAST_DEVICEINTERFACE NotificationFilter;

    ZeroMemory( &NotificationFilter, sizeof(NotificationFilter) );
    NotificationFilter.dbcc_size = sizeof(DEV_BROADCAST_DEVICEINTERFACE);
    NotificationFilter.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
    NotificationFilter.dbcc_classguid = InterfaceClassGuid;

    *hDeviceNotify = RegisterDeviceNotification( 
        hWnd,                       // events recipient
        &NotificationFilter,        // type of device
        DEVICE_NOTIFY_WINDOW_HANDLE // type of recipient handle
        );

    if ( NULL == *hDeviceNotify ) 
    {
        ErrorHandler(TEXT("RegisterDeviceNotification"));
        return FALSE;
    }

    return TRUE;
}

//
// MessagePump
//
void MessagePump(
    HWND hWnd
)
// Routine Description:
//     Simple main thread message pump.
//

// Parameters:
//     hWnd - handle to the window whose messages are being dispatched

// Return Value:
//     None.
{
    MSG msg; 
    int retVal;

    // Get all messages for any window that belongs to this thread,
    // without any filtering. Potential optimization could be
    // obtained via use of filter values if desired.

    while( (retVal = GetMessage(&msg, NULL, 0, 0)) != 0 ) 
    { 
        if ( retVal == -1 )
        {
            ErrorHandler(TEXT("GetMessage"));
            break;
        }
        else
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    } 
}

//
// WinProcCallback
//
INT_PTR WINAPI WinProcCallback(
                              HWND hWnd,
                              UINT message,
                              WPARAM wParam,
                              LPARAM lParam
                              )
// Routine Description:
//     Simple Windows callback for handling messages.
//     This is where all the work is done because the example
//     is using a window to process messages. This logic would be handled 
//     differently if registering a service instead of a window.

// Parameters:
//     hWnd - the window handle being registered for events.

//     message - the message being interpreted.

//     wParam and lParam - extended information provided to this
//          callback by the message sender.

//     For more information regarding these parameters and return value,
//     see the documentation for WNDCLASSEX and CreateWindowEx.
{
    LRESULT lRet = 1;
    static HDEVNOTIFY hDeviceNotify;
    static HWND hEditWnd;
    static ULONGLONG msgCount = 0;

    switch (message)
    {
    case WM_CREATE:
        //
        // This is the actual registration., In this example, registration 
        // should happen only once, at application startup when the window
        // is created.
        //
        // If you were using a service, you would put this in your main code 
        // path as part of your service initialization.
        //
        if ( ! DoRegisterDeviceInterfaceToHwnd(
                        WceusbshGUID, 
                        hWnd,
                        &hDeviceNotify) )
        {
            // Terminate on failure.
            ErrorHandler(TEXT("DoRegisterDeviceInterfaceToHwnd"));
            ExitProcess(1);
        }


        //
        // Make the child window for output.
        //
        hEditWnd = CreateWindow(TEXT("EDIT"),// predefined class 
                                NULL,        // no window title 
                                WS_CHILD | WS_VISIBLE | WS_VSCROLL | 
                                ES_LEFT | ES_MULTILINE | ES_AUTOVSCROLL, 
                                0, 0, 0, 0,  // set size in WM_SIZE message 
                                hWnd,        // parent window 
                                (HMENU)1,    // edit control ID 
                                (HINSTANCE) GetWindowLong(hWnd, GWL_HINSTANCE), 
                                NULL);       // pointer not needed 

        if ( hEditWnd == NULL )
        {
            // Terminate on failure.
            ErrorHandler(TEXT("CreateWindow: Edit Control"));
            ExitProcess(1);
        }
        // Add text to the window. 
        SendMessage(hEditWnd, WM_SETTEXT, 0, 
            (LPARAM)TEXT("Registered for USB device notification...\n")); 

        break;

    case WM_SETFOCUS: 
        SetFocus(hEditWnd); 

        break;

    case WM_SIZE: 
        // Make the edit control the size of the window's client area. 
        MoveWindow(hEditWnd, 
                   0, 0,                  // starting x- and y-coordinates 
                   LOWORD(lParam),        // width of client area 
                   HIWORD(lParam),        // height of client area 
                   TRUE);                 // repaint window 

        break;

    case WM_DEVICECHANGE:
    {
        //
        // This is the actual message from the interface via Windows messaging.
        // This code includes some additional decoding for this particular device type
        // and some common validation checks.
        //
        // Note that not all devices utilize these optional parameters in the same
        // way. Refer to the extended information for your particular device type 
        // specified by your GUID.
        //
        PDEV_BROADCAST_DEVICEINTERFACE b = (PDEV_BROADCAST_DEVICEINTERFACE) lParam;
        TCHAR strBuff[256];

        // Output some messages to the window.
        switch (wParam)
        {
        case DBT_DEVICEARRIVAL:
            msgCount++;
            StringCchPrintf(
                strBuff, 256, 
                TEXT("Message %d: DBT_DEVICEARRIVAL\n"), msgCount);
            break;
        case DBT_DEVICEREMOVECOMPLETE:
            msgCount++;
            StringCchPrintf(
                strBuff, 256, 
                TEXT("Message %d: DBT_DEVICEREMOVECOMPLETE\n"), msgCount);
            break;
        case DBT_DEVNODES_CHANGED:
            msgCount++;
            StringCchPrintf(
                strBuff, 256, 
                TEXT("Message %d: DBT_DEVNODES_CHANGED\n"), msgCount);
            break;
        default:
            msgCount++;
            StringCchPrintf(
                strBuff, 256, 
                TEXT("Message %d: WM_DEVICECHANGE message received, value %d unhandled.\n"), 
                msgCount, wParam);
            break;
        }
        OutputMessage(hEditWnd, wParam, (LPARAM)strBuff);
    }
            break;
    case WM_CLOSE:
        if ( ! UnregisterDeviceNotification(hDeviceNotify) )
        {
           ErrorHandler(TEXT("UnregisterDeviceNotification")); 
        }
        DestroyWindow(hWnd);
        break;

    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    default:
        // Send all other messages on to the default windows handler.
        lRet = DefWindowProc(hWnd, message, wParam, lParam);
        break;
    }

    return lRet;
}

#define WND_CLASS_NAME TEXT("SampleAppWindowClass")

//
// InitWindowClass
//
BOOL InitWindowClass()
// Routine Description:
//      Simple wrapper to initialize and register a window class.

// Parameters:
//     None

// Return Value:
//     TRUE on success, FALSE on failure.

// Note: 
//     wndClass.lpfnWndProc and wndClass.lpszClassName are the
//     important unique values used with CreateWindowEx and the
//     Windows message pump.
{
    WNDCLASSEX wndClass;

    wndClass.cbSize = sizeof(WNDCLASSEX);
    wndClass.style = CS_OWNDC | CS_HREDRAW | CS_VREDRAW;
    wndClass.hInstance = reinterpret_cast<HINSTANCE>(GetModuleHandle(0));
    wndClass.lpfnWndProc = reinterpret_cast<WNDPROC>(WinProcCallback);
    wndClass.cbClsExtra = 0;
    wndClass.cbWndExtra = 0;
    wndClass.hIcon = LoadIcon(0,IDI_APPLICATION);
    wndClass.hbrBackground = CreateSolidBrush(RGB(192,192,192));
    wndClass.hCursor = LoadCursor(0, IDC_ARROW);
    wndClass.lpszClassName = WND_CLASS_NAME;
    wndClass.lpszMenuName = NULL;
    wndClass.hIconSm = wndClass.hIcon;


    if ( ! RegisterClassEx(&wndClass) )
    {
        ErrorHandler(TEXT("RegisterClassEx"));
        return FALSE;
    }
    return TRUE;
}

//
// main
//

int __stdcall _tWinMain(
                      HINSTANCE hInstanceExe, 
                      HINSTANCE, // should not reference this parameter
                      PTSTR lpstrCmdLine, 
                      int nCmdShow
                      )
{
//
// To enable a console project to compile this code, set
// Project->Properties->Linker->System->Subsystem: Windows.
//

    int nArgC = 0;
    PWSTR* ppArgV = CommandLineToArgvW(lpstrCmdLine, &nArgC);
    g_pszAppName = ppArgV[0];

    if ( ! InitWindowClass() )
    {
        // InitWindowClass displays any errors
        return -1;
    }

    // Main app window

    HWND hWnd = CreateWindowEx(
                    WS_EX_CLIENTEDGE | WS_EX_APPWINDOW,
                    WND_CLASS_NAME,
                    g_pszAppName,
                    WS_OVERLAPPEDWINDOW, // style
                    CW_USEDEFAULT, 0, 
                    640, 480,
                    NULL, NULL, 
                    hInstanceExe, 
                    NULL);

    if ( hWnd == NULL )
    {
        ErrorHandler(TEXT("CreateWindowEx: main appwindow hWnd"));
        return -1;
    }

    // Actually draw the window.

    ShowWindow(hWnd, SW_SHOWNORMAL);
    UpdateWindow(hWnd);

    // The message pump loops until the window is destroyed.

    MessagePump(hWnd);

    return 1;
}

//
// OutputMessage
//
void OutputMessage(
    HWND hOutWnd, 
    WPARAM wParam, 
    LPARAM lParam
)
// Routine Description:
//     Support routine.
//     Send text to the output window, scrolling if necessary.

// Parameters:
//     hOutWnd - Handle to the output window.
//     wParam  - Standard windows message code, not used.
//     lParam  - String message to send to the window.

// Return Value:
//     None

// Note:
//     This routine assumes the output window is an edit control
//     with vertical scrolling enabled.

//     This routine has no error checking.
{
    LRESULT   lResult;
    LONG      bufferLen;
    LONG      numLines;
    LONG      firstVis;

    // Make writable and turn off redraw.
    lResult = SendMessage(hOutWnd, EM_SETREADONLY, FALSE, 0L);
    lResult = SendMessage(hOutWnd, WM_SETREDRAW, FALSE, 0L);

    // Obtain current text length in the window.
    bufferLen = SendMessage (hOutWnd, WM_GETTEXTLENGTH, 0, 0L);
    numLines = SendMessage (hOutWnd, EM_GETLINECOUNT, 0, 0L);
    firstVis = SendMessage (hOutWnd, EM_GETFIRSTVISIBLELINE, 0, 0L);
    lResult = SendMessage (hOutWnd, EM_SETSEL, bufferLen, bufferLen);

    // Write the new text.
    lResult = SendMessage (hOutWnd, EM_REPLACESEL, 0, lParam);

    // See whether scrolling is necessary.
    if (numLines > (firstVis + 1))
    {
        int        lineLen = 0;
        int        lineCount = 0;
        int        charPos;

        // Find the last nonblank line.
        numLines--;
        while(!lineLen)
        {
            charPos = SendMessage(
                hOutWnd, EM_LINEINDEX, (WPARAM)numLines, 0L);
            lineLen = SendMessage(
                hOutWnd, EM_LINELENGTH, charPos, 0L);
            if(!lineLen)
                numLines--;
        }
        // Prevent negative value finding min.
        lineCount = numLines - firstVis;
        lineCount = (lineCount >= 0) ? lineCount : 0;

        // Scroll the window.
        lResult = SendMessage(
            hOutWnd, EM_LINESCROLL, 0, (LPARAM)lineCount);
    }

    // Done, make read-only and allow redraw.
    lResult = SendMessage(hOutWnd, WM_SETREDRAW, TRUE, 0L);
    lResult = SendMessage(hOutWnd, EM_SETREADONLY, TRUE, 0L);
}  

//
// ErrorHandler
//
void ErrorHandler(
   LPTSTR lpszFunction
) 
// Routine Description:
//     Support routine.
//     Retrieve the system error message for the last-error code
//     and pop a modal alert box with usable info.

// Parameters:
//     lpszFunction - String containing the function name where 
//     the error occurred plus any other relevant data you'd 
//     like to appear in the output. 

// Return Value:
//     None

// Note:
//     This routine is independent of the other windowing routines
//     in this application and can be used in a regular console
//     application without modification.
{ 

    LPVOID lpMsgBuf;
    LPVOID lpDisplayBuf;
    DWORD dw = GetLastError(); 

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        dw,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR) &lpMsgBuf,
        0, NULL );

    // Display the error message and exit the process.

    lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT, 
        (lstrlen((LPCTSTR)lpMsgBuf)
                  + lstrlen((LPCTSTR)lpszFunction)+40)
                  * sizeof(TCHAR)); 
    StringCchPrintf((LPTSTR)lpDisplayBuf, 
        LocalSize(lpDisplayBuf) / sizeof(TCHAR),
        TEXT("%s failed with error %d: %s"), 
        lpszFunction, dw, lpMsgBuf); 
    MessageBox(NULL, (LPCTSTR)lpDisplayBuf, g_pszAppName, MB_OK); 

    LocalFree(lpMsgBuf);
    LocalFree(lpDisplayBuf);
}

The following is an example makefile for building the previous example code using nmake.exe from the SDK or Visual Studio command prompt.

proj = main

all: $(proj).exe

# Update the object file if necessary

$(proj).obj: $(proj).cpp
  cl -c  /D_UNICODE /DUNICODE -DWIN32 -D_WIN32 -DNDEBUG -GS -D_X86_=1 -D_WIN32_WINNT=0x0501 -DCRTAPI1=_cdecl -DCRTAPI2=_cdecl -D_MT -D_DLL -MD $*.cpp

# Update the executable file if necessary

$(proj).exe: $(proj).obj
  link -release -incremental:no -nologo -subsystem:windows,5.01 $(proj).obj kernel32.lib user32.lib advapi32.lib gdi32.lib shell32.lib -out:$(proj).exe