Handling Windows USB events

Question

I created a generic USB HID comms driver capable of monitoring USB events and sending/receiving data packets to and from devices. I\'ve been using it successfully since my

Answer 1

After doing a bit of research, it seems that Windows messaging is a necessary part of handling USB Device Change notifications. I have a working usb comms driver class which includes a simple implementation. This solution consists of two parts, 1) the EventNotifier class, which generates the events and 2) the 'receiver', which subscribes to the events (i.e. a client that gets notified of USB events). The sample code is C++/CLI and although I don't subscribe to the practice of putting executable code in header files, for the sake of brevity, I do so here.

#pragma once

#include     // Declares required datatypes.
#include         // Required for WM_DEVICECHANGE messages.
#include    // Required for DEFINE_GUID definition (see below).

namespace USBComms 
{
    using namespace System;
    using namespace System::Runtime::InteropServices;
    using namespace System::Windows;
    using namespace System::Windows::Forms;

    // This function is required for receieving WM_DEVICECHANGE messages.
    // Note: name is remapped "RegisterDeviceNotificationUM"
    [DllImport("user32.dll" , CharSet = CharSet::Unicode, EntryPoint="RegisterDeviceNotification")]                 
    extern "C" HDEVNOTIFY WINAPI RegisterDeviceNotificationUM(
        HANDLE hRecipient,
        LPVOID NotificationFilter,
        DWORD Flags);

    // Generic guid for usb devices (see e.g. http://msdn.microsoft.com/en-us/library/windows/hardware/ff545972%28v=vs.85%29.aspx).
    // Note: GUIDs are device and OS specific and may require modification. Using the wrong guid will cause notification to fail.
    // You may have to tinker with your device to find the appropriate GUID. "hid.dll" has a function `HidD_GetHidGuid' that returns
    // "the device interfaceGUID for HIDClass devices" (see http://msdn.microsoft.com/en-us/library/windows/hardware/ff538924%28v=vs.85%29.aspx).
    // However, testing revealed it does not always return a useful value. The GUID_DEVINTERFACE_USB_DEVICE value, defined as
    // {A5DCBF10-6530-11D2-901F-00C04FB951ED}, has worked with cell phones, thumb drives, etc. For more info, see e.g.
    // http://msdn.microsoft.com/en-us/library/windows/hardware/ff553426%28v=vs.85%29.aspx. 
    DEFINE_GUID(GUID_DEVINTERFACE_USB_DEVICE, 0xA5DCBF10L, 0x6530, 0x11D2, 0x90, 0x1F, 0x00, 0xC0, 0x4F, 0xB9, 0x51, 0xED);

    /// 

    /// Declare a delegate for the notification event handler.
    /// 
    /// The object where the event handler is attached.
    /// The event data.
    public delegate void NotificationEventHandler(Object^ sender, EventArgs^ e);

    /// 

    /// Class that generetaes USB Device Change notification events.
    /// 
    /// 
    /// A Form is not necessary. Any type wherein you can override WndProc() can be used.
    /// 
    public ref class EventNotifier : public Control
    {
    private:
        /// 

        /// Raises the NotificationEvent.
        /// 
        /// The event data.
        void RaiseNotificationEvent(EventArgs^ e) {
            NotificationEvent(this, e);
        }

    protected:
        /// 

        /// Overrides the base class WndProc method.
        /// 
        /// The Windows Message to process. 
        /// 
        /// This method receives Windows Messages (WM_xxxxxxxxxx) and
        /// raises our NotificationEvent as appropriate. Here you should
        /// add any message filtering (e.g. for the WM_DEVICECHANGE) and
        /// preprocessing before raising the event (or not).
        /// 
        virtual void WndProc(Message% message) override {
            if(message.Msg == WM_DEVICECHANGE)
            {
                RaiseNotificationEvent(EventArgs::Empty);
            }
            __super::WndProc(message);
        }

    public:
        /// 

        /// Creates a new instance of the EventNotifier class.
        /// 
        EventNotifier(void) {
            RequestNotifications(this->Handle); // Register ourselves as the Windows Message processor.
        }

        /// 

        /// Registers an object, identified by the handle, for
        /// Windows WM_DEVICECHANGE messages.
        /// 
        /// The object's handle.
        void RequestNotifications(IntPtr handle) {
            GUID InterfaceClassGuid = GUID_DEVINTERFACE_USB_DEVICE;
            DEV_BROADCAST_DEVICEINTERFACE MyDeviceBroadcastHeader;

            MyDeviceBroadcastHeader.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
            MyDeviceBroadcastHeader.dbcc_size = sizeof(DEV_BROADCAST_DEVICEINTERFACE);
            MyDeviceBroadcastHeader.dbcc_reserved = 0;
            MyDeviceBroadcastHeader.dbcc_classguid = InterfaceClassGuid;
            RegisterDeviceNotificationUM((HANDLE)handle, &MyDeviceBroadcastHeader, DEVICE_NOTIFY_WINDOW_HANDLE);
        }

        /// 

        /// Defines the notification event.
        /// 
        virtual event NotificationEventHandler^ NotificationEvent;
    };
}

Then, in the 'receiver' (the object that subscribes to and consumes our NotificationEvent, all you have to do is:

void Receiver::SomeFunction(void)
{
    USBComms::EventNotifier usb = gcnew USBComms::EventNotifier();

    usb->NotificationEvent += gcnew USBComms::NotificationEventHandler(this, &Receiver::USBEvent);
}

void Receiver::USBEvent(Object^ sender, EventArgs^ e)
{
    // Handle the event notification as appropriate.
}