Question

I want to differentiate between (barcode) scanner and keyboard input in an WPF application.
What I need is an event which occurs whenever my scanner is providing data.

In my application there is a special field which will be filled with the input from the scanner. So, if the user has focused an other field I don’t want to insert the scanned code in that, but my special field.

First of all I switch the input mode of my scanner (connected by USB) from “keyboard emulation” to “raw”. But what do I need to do now?

Answer 1

I’ve discarded my approach to realize this with POS for .NET. It’s almost easier to do it yourself, in so far as you the scanner handling it the only relevant part of the framework you were interested in. Here’s basically what I’m using:

public class RawInput
{
    private static IntPtr DispatchMessage(IntPtr lParam, IEnumerable<IntPtr> fromDevices, ref object data)
    {
        var dataSize = UIntPtr.Zero;
        if (Win32.GetRawInputData(lParam, (UIntPtr)CommandFlag.Input, IntPtr.Zero, ref dataSize, (UIntPtr)Marshal.SizeOf(typeof(Win32.RAWINPUTHEADER))) == UIntPtr.Zero)
        {
            var buff = Marshal.AllocHGlobal((int)dataSize);
            var outSize = Win32.GetRawInputData(lParam, (UIntPtr)CommandFlag.Input, buff, ref dataSize, (UIntPtr)Marshal.SizeOf(typeof(Win32.RAWINPUTHEADER)));

            Debug.Assert(outSize == dataSize);
            var input = (Win32.RAWINPUT)Marshal.PtrToStructure(buff, typeof(Win32.RAWINPUT));

            var hDevice = IntPtr.Zero;
            if (fromDevices == null)
                hDevice = input.header.hDevice;
            else
                hDevice = fromDevices.FirstOrDefault(h => h == input.header.hDevice);

            if (hDevice != IntPtr.Zero)
            {
                switch ((Type)input.header.dwType)
                {
                    case Type.HID:
                        var hidData = new HIDDATA()
                        {
                            count = input.hid.dwCount,
                            size = input.hid.dwSizeHid,
                            raw = new byte[input.hid.dwCount * input.hid.dwSizeHid]
                        };

                        Marshal.Copy(
                            new IntPtr(
                                buff.ToInt64() +
                                Marshal.SizeOf(typeof(Win32.RAWINPUTHEADER)) +
                                Marshal.SizeOf(typeof(Win32.RAWHID))
                            ),
                            hidData.raw, 0, hidData.raw.Length
                        );

                        data = hidData;
                        break;
                    case Type.Keyboard:
                        data = new KEYBOARDDATA
                        {
                            makeCode = input.keyboard.MakeCode,
                            flags = (KeyboardFlag)input.keyboard.Flags,
                            vKey = input.keyboard.VKey,
                            message = (MessageContext)input.keyboard.Message,
                            extraInfo = input.keyboard.ExtraInformation
                        };
                        break;
                    case Type.Mouse:
                        var mouseData = new MOUSEDATA
                        {
                            extraInfo = input.mouse.ulExtraInformation,
                            flags = (MouseFlag)input.mouse.usFlags,
                            transitions = (MouseTransition)input.mouse.usButtonFlags,
                            motionX = input.mouse.lLastX,
                            motionY = input.mouse.lLastY
                        };

                        if (mouseData.transitions == MouseTransition.MouseWheel)
                            mouseData.wheelDelta = input.mouse.usButtonData;
                        data = mouseData;
                        break;
                }
            }

            Marshal.FreeHGlobal(buff);
            return hDevice;
        }
        else
            throw new ApplicationException("An error occurred while receiving raw input data.");
    }

    public static bool DispatchMessage(Win32.MSG message, IEnumerable<Device> fromDevices, ref Device source, ref object data)
    {
        var hDevice = IntPtr.Zero;
        if (message.message == MessageContext.Input)
        {
            if (fromDevices != null)
            {
                hDevice = DispatchMessage(message.lParam, fromDevices.Select(h => h.Handle), ref data);
                if (hDevice != IntPtr.Zero)
                    source = fromDevices.First(h => h.Handle == hDevice);
            }
            else
            {
                Func<Device> getRawInputDeviceInfo = () =>
                {
                    var name_size = UIntPtr.Zero;
                    Win32.GetRawInputDeviceInfo(hDevice, (UIntPtr)Win32.RIDI_DEVICENAME, IntPtr.Zero, ref name_size);

                    if (name_size != UIntPtr.Zero)
                    {
                        var name = Marshal.AllocHGlobal((int)name_size);
                        Win32.GetRawInputDeviceInfo(hDevice, (UIntPtr)Win32.RIDI_DEVICENAME, name, ref name_size);
                        string rid_name = (string)Marshal.PtrToStringAnsi(name);

                        var ridSize = (UIntPtr)Marshal.SizeOf(typeof(Win32.RID_DEVICE_INFO));
                        var buff = Marshal.AllocHGlobal((int)ridSize);
                        var outSize = Win32.GetRawInputDeviceInfo(hDevice, (UIntPtr)Win32.RIDI_DEVICEINFO, buff, ref ridSize);
                        Debug.Assert(outSize == ridSize);

                        var rid = (Win32.RID_DEVICE_INFO)Marshal.PtrToStructure(buff, typeof(Win32.RID_DEVICE_INFO));

                        var device = new Device()
                        {
                            Handle = hDevice,
                            ID = rid_name,
                            Type = (Type)rid.dwType,
                            Description = GetRawInputDeviceDescription(rid_name)
                        };

                        Marshal.FreeHGlobal(name);
                        return device;
                    }

                    return null;
                };

                hDevice = DispatchMessage(message.lParam, null, ref data);
                if (hDevice != IntPtr.Zero)
                    source = getRawInputDeviceInfo();
            }
        }

        return hDevice != IntPtr.Zero;
    }

    public static IEnumerable<Device> EnumerateDevices()
    {
        var ridSize = (UIntPtr)Marshal.SizeOf(typeof(Win32.RAWINPUTDEVICELIST));
        var ridCnt = UIntPtr.Zero;
        var list = new List<Device>();

        if (Win32.GetRawInputDeviceList(IntPtr.Zero, ref ridCnt, ridSize) == UIntPtr.Zero)
        {
            var buff = Marshal.AllocHGlobal((int)ridCnt * (int)ridSize);
            Win32.GetRawInputDeviceList(buff, ref ridCnt, ridSize);

            for (int i = 0; i < (int)ridCnt; ++i)
            {
                var rid = (Win32.RAWINPUTDEVICELIST)Marshal.PtrToStructure(
                    new IntPtr((buff.ToInt64() + (int)ridSize * i)),
                    typeof(Win32.RAWINPUTDEVICELIST)
                );

                var nameSize = UIntPtr.Zero;
                Win32.GetRawInputDeviceInfo(rid.hDevice, (UIntPtr)Win32.RIDI_DEVICENAME, IntPtr.Zero, ref nameSize);

                if (nameSize != UIntPtr.Zero)
                {
                    var name = Marshal.AllocHGlobal((int)nameSize);
                    Win32.GetRawInputDeviceInfo(rid.hDevice, (UIntPtr)Win32.RIDI_DEVICENAME, name, ref nameSize);
                    string rid_id = (string)Marshal.PtrToStringAnsi(name);

                    // filter Terminal Services and Remote Desktop devices.
                    if (!rid_id.ToUpper().Contains("ROOT"))
                    {
                        yield return new Device()
                        {
                            Handle = rid.hDevice,
                            ID = rid_id,
                            Type = (Type)rid.dwType,
                            Description = GetRawInputDeviceDescription(rid_id)
                        };

                        Marshal.FreeHGlobal(name);
                    }
                }
            }

            Marshal.FreeHGlobal(buff);
        }
        else
            throw new ApplicationException("An error occurred while retrieving a list of raw input devices");
    }

    public static void Register(IntPtr hwnd, REGISTERCLASS[] regs)
    {
        Debug.Assert(hwnd != IntPtr.Zero);

        // Usage Pages and Usages:
        // http://www.usb.org/developers/devclass_docs/Hut1_12.pdf

        var rid = new Win32.RAWINPUTDEVICE[regs.Length];
        for (int i = 0; i < regs.Length; ++i)
        {
            rid[i].dwFlags = (uint)regs[i].flags;
            rid[i].usUsage = regs[i].usage;
            rid[i].usUsagePage = (ushort)regs[i].usagePage;
            rid[i].hwndTarget = hwnd;
        }

        if (Win32.RegisterRawInputDevices(rid, (UIntPtr)rid.Length, (UIntPtr)Marshal.SizeOf(typeof(Win32.RAWINPUTDEVICE))) == IntPtr.Zero)
            throw new ApplicationException("Failed to register raw input devices");
    }

    public class Device
    {
        public static bool operator ==(Device x, Device y) { if ((object)x != null & (object)y != null) { return x.Handle == y.Handle; } else return (object)x == null && (object)y == null; }
        public static bool operator !=(Device x, Device y) { return !(x == y); }

        public override bool Equals(object obj) { return this == (Device)obj; }
        public override int GetHashCode() { return base.GetHashCode(); }

        public IntPtr Handle { get; set; }
        public Type Type { get; set; }
        public string ID { get; set; }
        public string Description { get; set; }
    }

    public struct HIDDATA
    {
        public uint size;
        public uint count;
        public byte[] raw;
    }

    public struct KEYBOARDDATA
    {
        public ushort makeCode;
        public KeyboardFlag flags;
        public ushort vKey;
        public MessageContext message;
        public uint extraInfo;
    }

    public struct MOUSEDATA
    {
        public MouseFlag flags;
        public MouseTransition transitions;
        public ushort wheelDelta;
        public int motionX;
        public int motionY;
        public uint extraInfo;
    }

    public struct REGISTERCLASS
    {
        public UsagePage usagePage;
        public ushort usage;
        public ModeFlag flags;
    }

    public enum KeyboardFlag : ushort
    {
        KeyUp = Win32.RI_KEY_BREAK,
        KeyDown = Win32.RI_KEY_MAKE,
        KeyLeft = Win32.RI_KEY_E0,
        KeyRight = Win32.RI_KEY_E1
    }

    public enum MouseFlag : ushort
    {
        AttributesChanged = Win32.MOUSE_ATTRIBUTES_CHANGED,
        MoveRelative = Win32.MOUSE_MOVE_RELATIVE,
        MoveAbsolute = Win32.MOUSE_MOVE_ABSOLUTE,
        VirtualDesktop = Win32.MOUSE_VIRTUAL_DESKTOP
    }

    public enum MouseTransition : ushort
    {
        LeftButtonDown = Win32.RI_MOUSE_LEFT_BUTTON_DOWN,
        LeftButtonUp = Win32.RI_MOUSE_LEFT_BUTTON_UP,
        MiddleButtonDown = Win32.RI_MOUSE_MIDDLE_BUTTON_DOWN,
        MiddleButtonUp = Win32.RI_MOUSE_MIDDLE_BUTTON_UP,
        RightButtonDown = Win32.RI_MOUSE_RIGHT_BUTTON_DOWN,
        RightButtonUp = Win32.RI_MOUSE_RIGHT_BUTTON_UP,
        XButton1Down = Win32.RI_MOUSE_BUTTON_4_DOWN,
        XButton1Up = Win32.RI_MOUSE_BUTTON_4_UP,
        XButton2Down = Win32.RI_MOUSE_BUTTON_5_DOWN,
        XButton2Up = Win32.RI_MOUSE_BUTTON_5_UP,
        MouseWheel = Win32.RI_MOUSE_WHEEL
    }

    public enum CommandFlag
    {
        Header = Win32.RID_HEADER,
        Input = Win32.RID_INPUT
    }

    public enum ModeFlag : uint
    {
        Default = 0,
        ApplicationKeys = Win32.RIDEV_APPKEYS,
        CaptureMouse = Win32.RIDEV_CAPTUREMOUSE,
        DeviceNotify = Win32.RIDEV_DEVNOTIFY,
        Exclude = Win32.RIDEV_EXCLUDE,
        ExcludeInputSink = Win32.RIDEV_EXINPUTSINK,
        InputSink = Win32.RIDEV_INPUTSINK,
        NoHotKeys = Win32.RIDEV_NOHOTKEYS,
        NoLegacy = Win32.RIDEV_NOLEGACY,
        PageOnly = Win32.RIDEV_PAGEONLY,
        Remove = Win32.RIDEV_REMOVE
    };

    public enum UsagePage : ushort
    {
        Undefined = 0x00,
        GenericDesktopControls = 0x01,
        SimulationControls = 0x02,
        VRControls = 0x03,
        SportControls = 0x04,
        GameControls = 0x05,
        GenericDeviceControls = 0x06,
        Keyboard = 0x07,
        Keypad = Keyboard,
        LEDs = 0x08,
        Button = 0x09,
        Ordinal = 0x0a,
        Telephony = 0x0b,
        Consumer = 0x0c,
        Digitizer = 0x0d,
        PIDPage = 0x0f,
        Unicode = 0x10,
        AlphanumericDisplay = 0x14,
        MedicalInstruments = 0x40,
        MonitorPage0 = 0x80,
        MonitorPage1 = 0x81,
        MonitorPage2 = 0x82,
        MonitorPage3 = 0x83,
        PowerPage0 = 0x84,
        PowerPage1 = 0x85,
        PowerPage2 = 0x86,
        PowerPage3 = 0x87,
        BarCodeScannerPages = 0x8c,
        Scale = 0x8d,
        MagneticStripeReadingDevices = 0x8e,
        ReservedPointofSalePages = 0x8f,
        CameraControlPage = 0x90,
        ArcadePage = 0x91
    }

    /// <see cref="http://www.usb.org/developers/devclass_docs/pos1_02.pdf"/>
    public enum BarCodeScannerPages : ushort
    {
        BarCodeScanner = 0x0002
    }

    public enum Type : uint
    {
        Mouse = Win32.RIM_TYPEMOUSE,
        Keyboard = Win32.RIM_TYPEKEYBOARD,
        HID = Win32.RIM_TYPEHID
    }

    private static string GetRawInputDeviceDescription(string deviceid)
    {
        string[] id = deviceid.Substring(4).Split('#');

        // get registry entry by appropriate key
        return ((string)Registry.LocalMachine.OpenSubKey(string.Format(
            @"System\CurrentControlSet\Enum\{0}\{1}\{2}",
            id[0], id[1], id[2]), false
        ).GetValue("DeviceDesc")).Split(';')[1];
    }
}

The class Win32 imports the used Win32 API functions and contains some constants used by them:

public static class Win32
{
    // mouse state flags
    public const ushort MOUSE_ATTRIBUTES_CHANGED = 4, // Mouse attributes changed; application needs to query the mouse attributes.
                        MOUSE_MOVE_RELATIVE = 0, // Mouse movement data is relative to the last mouse position.
                        MOUSE_MOVE_ABSOLUTE = 1, // Mouse movement data is based on absolute position.
                        MOUSE_VIRTUAL_DESKTOP = 2; // Mouse coordinates are mapped to the virtual desktop (for a multiple monitor system).

    // mouse transition state flags
    public const ushort RI_MOUSE_LEFT_BUTTON_DOWN = 0x0001, // Left button changed to down.
                        RI_MOUSE_LEFT_BUTTON_UP = 0x0002, // Left button changed to up.
                        RI_MOUSE_MIDDLE_BUTTON_DOWN = 0x0010, // Middle button changed to down.
                        RI_MOUSE_MIDDLE_BUTTON_UP = 0x0020, // Middle button changed to up.
                        RI_MOUSE_RIGHT_BUTTON_DOWN = 0x0004, // Right button changed to down.
                        RI_MOUSE_RIGHT_BUTTON_UP = 0x0008, // Right button changed to up.
                        RI_MOUSE_BUTTON_1_DOWN = 0x0001, // RI_MOUSE_LEFT_BUTTON_DOWN
                        RI_MOUSE_BUTTON_1_UP = 0x0002, // RI_MOUSE_LEFT_BUTTON_UP
                        RI_MOUSE_BUTTON_2_DOWN = 0x0004, // RI_MOUSE_RIGHT_BUTTON_DOWN
                        RI_MOUSE_BUTTON_2_UP = 0x0008, // RI_MOUSE_RIGHT_BUTTON_UP
                        RI_MOUSE_BUTTON_3_DOWN = 0x0010, // RI_MOUSE_MIDDLE_BUTTON_DOWN
                        RI_MOUSE_BUTTON_3_UP = 0x0020, // RI_MOUSE_MIDDLE_BUTTON_UP
                        RI_MOUSE_BUTTON_4_DOWN = 0x0040, // XBUTTON1 changed to down.
                        RI_MOUSE_BUTTON_4_UP = 0x0080, // XBUTTON1 changed to up.
                        RI_MOUSE_BUTTON_5_DOWN = 0x0100, // XBUTTON2 changed to down.
                        RI_MOUSE_BUTTON_5_UP = 0x0200, // XBUTTON2 changed to up.
                        RI_MOUSE_WHEEL = 0x0400; // Raw input comes from a mouse wheel. The wheel delta is stored in usButtonData.

    // keyboard scan code flags
    public const ushort RI_KEY_BREAK = 1,
                        RI_KEY_E0 = 2,
                        RI_KEY_E1 = 4,
                        RI_KEY_MAKE = 0;

    // device types
    public const int RIM_TYPEMOUSE = 0,
                     RIM_TYPEKEYBOARD = 1,
                     RIM_TYPEHID = 2;

    public const int RIDI_PREPARSEDDATA = 0x20000005,
                     RIDI_DEVICENAME = 0x20000007, // the return valus is the character length, not the byte size
                     RIDI_DEVICEINFO = 0x2000000b;

    // mode flags
    public const int RIDEV_REMOVE = 0x00000001,
                     RIDEV_EXCLUDE = 0x00000010,
                     RIDEV_PAGEONLY = 0x00000020,
                     RIDEV_NOLEGACY = 0x00000030,
                     RIDEV_INPUTSINK = 0x00000100,
                     RIDEV_CAPTUREMOUSE = 0x00000200, // effective when mouse nolegacy is specified, otherwise it would be an error
                     RIDEV_NOHOTKEYS = 0x00000200, // effective for keyboard.
                     RIDEV_APPKEYS = 0x00000400, // effective for keyboard.
                     RIDEV_EXINPUTSINK = 0x00001000,
                     RIDEV_DEVNOTIFY = 0x00002000,
                     RIDEV_EXMODEMASK = 0x000000F0;

    // command flag
    public const int RID_HEADER = 0x10000005,
                     RID_INPUT = 0x10000003;    

    /// <summary>
    /// Contains information about a raw input device.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWINPUTDEVICELIST {
    ///     HANDLE hDevice;
    ///     DWORD  dwType;
    /// } RAWINPUTDEVICELIST, *PRAWINPUTDEVICELIST;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RAWINPUTDEVICELIST
    {
        public IntPtr hDevice;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwType;
    }

    /// <summary>
    /// Defines information for the raw input devices.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWINPUTDEVICE {
    ///     USHORT usUsagePage;
    ///     USHORT usUsage;
    ///     DWORD  dwFlags;
    ///     HWND   hwndTarget;
    /// } RAWINPUTDEVICE, *PRAWINPUTDEVICE, *LPRAWINPUTDEVICE;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RAWINPUTDEVICE
    {
        [MarshalAs(UnmanagedType.U2)]
        public ushort usUsagePage;
        [MarshalAs(UnmanagedType.U2)]
        public ushort usUsage;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwFlags;
        public IntPtr hwndTarget;
    }

    /// <summary>
    /// Contains information about the state of the mouse.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWMOUSE {
    ///     USHORT usFlags;
    ///     union {
    ///         ULONG  ulButtons;
    ///         struct {
    ///             USHORT usButtonFlags;
    ///             USHORT usButtonData;
    ///         };
    ///     };
    ///     ULONG  ulRawButtons;
    ///     LONG   lLastX;
    ///     LONG   lLastY;
    ///     ULONG  ulExtraInformation;
    /// } RAWMOUSE, *PRAWMOUSE, *LPRAWMOUSE;
    /// </remarks>
    [StructLayout(LayoutKind.Explicit)]
    public struct RAWMOUSE
    {
        [FieldOffset(0), MarshalAs(UnmanagedType.U2)]
        public ushort usFlags;
        [FieldOffset(4), MarshalAs(UnmanagedType.U4)]
        public uint ulButtons;
        [FieldOffset(4), MarshalAs(UnmanagedType.U2)]
        public ushort usButtonFlags;
        [FieldOffset(6), MarshalAs(UnmanagedType.U2)]
        public ushort usButtonData;
        [FieldOffset(8), MarshalAs(UnmanagedType.U4)]
        public uint ulRawButtons;
        [FieldOffset(12), MarshalAs(UnmanagedType.I4)]
        public int lLastX;
        [FieldOffset(16), MarshalAs(UnmanagedType.I4)]
        public int lLastY;
        [FieldOffset(20), MarshalAs(UnmanagedType.U4)]
        public uint ulExtraInformation;
    }

    /// <summary>
    /// Contains information about the state of the keyboard.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWKEYBOARD {
    ///     USHORT MakeCode;
    ///     USHORT Flags;
    ///     USHORT Reserved;
    ///     USHORT VKey;
    ///     UINT   Message;
    ///     ULONG  ExtraInformation;
    /// } RAWKEYBOARD, *PRAWKEYBOARD, *LPRAWKEYBOARD;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RAWKEYBOARD
    {
        [MarshalAs(UnmanagedType.U2)]
        public ushort MakeCode;
        [MarshalAs(UnmanagedType.U2)]
        public ushort Flags;
        [MarshalAs(UnmanagedType.U2)]
        public ushort Reserved;
        [MarshalAs(UnmanagedType.U2)]
        public ushort VKey;
        [MarshalAs(UnmanagedType.SysUInt)]
        public UIntPtr Message;
        [MarshalAs(UnmanagedType.U4)]
        public uint ExtraInformation;
    }

    /// <summary>
    /// Describes the format of the raw input from a Human Interface Device (HID).
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWHID {
    ///     DWORD dwSizeHid;
    ///     DWORD dwCount;
    ///     BYTE  bRawData[1];
    /// } RAWHID, *PRAWHID, *LPRAWHID;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RAWHID
    {
        [MarshalAs(UnmanagedType.U4)]
        public uint dwSizeHid;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwCount;
    }

    /// <summary>
    /// Contains the header information that is part of the raw input data.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWINPUTHEADER {
    ///     DWORD  dwType;
    ///     DWORD  dwSize;
    ///     HANDLE hDevice;
    ///     WPARAM wParam;
    /// } RAWINPUTHEADER, *PRAWINPUTHEADER;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RAWINPUTHEADER
    {
        [MarshalAs(UnmanagedType.U4)]
        public uint dwType;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwSize;
        public IntPtr hDevice;
        [MarshalAs(UnmanagedType.SysUInt)]
        public UIntPtr wParam;
    }

    /// <summary>
    /// Contains the raw input from a device.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRAWINPUT {
    ///     RAWINPUTHEADER header;
    ///     union {
    ///         RAWMOUSE    mouse;
    ///         RAWKEYBOARD keyboard;
    ///         RAWHID      hid;
    ///     } data;
    /// } RAWINPUT, *PRAWINPUT, *LPRAWINPUT;
    /// </remarks>
    [StructLayout(LayoutKind.Explicit)]
    public struct RAWINPUT
    {
        [FieldOffset(0)]
        public RAWINPUTHEADER header;
#if IA32
        [FieldOffset(16)]
        public RAWMOUSE mouse;
        [FieldOffset(16)]
        public RAWKEYBOARD keyboard;
        [FieldOffset(16)]
        public RAWHID hid;
#elif INTEL64
        [FieldOffset(24)]
        public RAWMOUSE mouse;
        [FieldOffset(24)]
        public RAWKEYBOARD keyboard;
        [FieldOffset(24)]
        public RAWHID hid;
#endif
    }

    /// <summary>
    /// Defines the raw input data coming from the specified keyboard.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRID_DEVICE_INFO_KEYBOARD {
    ///     DWORD dwType;
    ///     DWORD dwSubType;
    ///     DWORD dwKeyboardMode;
    ///     DWORD dwNumberOfFunctionKeys;
    ///     DWORD dwNumberOfIndicators;
    ///     DWORD dwNumberOfKeysTotal;
    /// } RID_DEVICE_INFO_KEYBOARD, *PRID_DEVICE_INFO_KEYBOARD;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RID_DEVICE_INFO_KEYBOARD
    {
        [MarshalAs(UnmanagedType.U4)]
        public uint dwType;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwSubType;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwKeyboardMode;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwNumberOfFunctionKeys;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwNumberOfIndicators;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwNumberOfKeysTotal;
    }

    /// <summary>
    /// Defines the raw input data coming from the specified mouse.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRID_DEVICE_INFO_MOUSE {
    ///     DWORD dwId;
    ///     DWORD dwNumberOfButtons;
    ///     DWORD dwSampleRate;
    ///     BOOL  fHasHorizontalWheel;
    /// } RID_DEVICE_INFO_MOUSE, *PRID_DEVICE_INFO_MOUSE;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RID_DEVICE_INFO_MOUSE
    {
        [MarshalAs(UnmanagedType.U4)]
        public uint dwId;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwNumberOfButtons;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwSampleRate;
        [MarshalAs(UnmanagedType.SysInt)]
        public IntPtr fHasHorizontalWheel;
    }

    /// <summary>
    /// Defines the raw input data coming from the specified Human Interface Device (HID).
    /// </summary>
    /// <remarks>
    /// typedef struct tagRID_DEVICE_INFO_HID {
    ///     DWORD  dwVendorId;
    ///     DWORD  dwProductId;
    ///     DWORD  dwVersionNumber;
    ///     USHORT usUsagePage;
    ///     USHORT usUsage;
    /// } RID_DEVICE_INFO_HID, *PRID_DEVICE_INFO_HID;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct RID_DEVICE_INFO_HID
    {
        [MarshalAs(UnmanagedType.U4)]
        public uint dwVendorId;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwProductId;
        [MarshalAs(UnmanagedType.U4)]
        public uint dwVersionNumber;
        [MarshalAs(UnmanagedType.U2)]
        public ushort usUsagePage;
        [MarshalAs(UnmanagedType.U2)]
        public ushort usUsage;
    }

    /// <summary>
    /// Defines the raw input data coming from any device.
    /// </summary>
    /// <remarks>
    /// typedef struct tagRID_DEVICE_INFO {
    ///     DWORD cbSize;
    ///     DWORD dwType;
    ///     union {
    ///         RID_DEVICE_INFO_MOUSE    mouse;
    ///         RID_DEVICE_INFO_KEYBOARD keyboard;
    ///         RID_DEVICE_INFO_HID      hid;
    ///     } ;
    /// } RID_DEVICE_INFO, *PRID_DEVICE_INFO, *LPRID_DEVICE_INFO;
    /// </remarks>
    [StructLayout(LayoutKind.Explicit)]
    public struct RID_DEVICE_INFO
    {
        [FieldOffset(0), MarshalAs(UnmanagedType.U4)]
        public uint cbSize;
        [FieldOffset(4), MarshalAs(UnmanagedType.U4)]
        public uint dwType;
        [FieldOffset(8)]
        public RID_DEVICE_INFO_MOUSE mouse;
        [FieldOffset(8)]
        public RID_DEVICE_INFO_KEYBOARD keyboard;
        [FieldOffset(8)]
        public RID_DEVICE_INFO_HID hid;
    }

    /// <summary>
    /// The POINT structure defines the x- and y- coordinates of a point.
    /// </summary>
    /// <remarks>
    /// typedef struct tagPOINT {
    ///     LONG x;
    ///     LONG y;
    /// } POINT, *PPOINT;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct POINT
    {
        [MarshalAs(UnmanagedType.U4)]
        public long x;
        [MarshalAs(UnmanagedType.U4)]
        public long y;
    } 

    /// <summary>
    /// Contains message information from a thread's message queue.
    /// </summary>
    /// <remarks>
    /// typedef struct tagMSG {
    ///     HWND   hwnd;
    ///     UINT   message;
    ///     WPARAM wParam;
    ///     LPARAM lParam;
    ///     DWORD  time;
    ///     POINT  pt;
    /// } MSG, *PMSG, *LPMSG;
    /// </remarks>
    [StructLayout(LayoutKind.Sequential)]
    public struct MSG
    {
        public IntPtr hwnd;
        [MarshalAs(UnmanagedType.SysUInt)]
        public MessageContext message;
        public IntPtr wParam;
        public IntPtr lParam;
        [MarshalAs(UnmanagedType.U4)]
        public ulong time;
        public POINT pt;
    }

    [DllImport("user32.dll")]
    public static extern bool SetForegroundWindow(IntPtr hWnd);     
    // ...
    // Import other API functions used above
    // ...
}