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reading from a USB keyboard (HID)

Hi guys,

I am trying to read from a USB keyboard using vb.net and HID classes. the
USB keyboard is not my primary keyboard. I have a ps2 keyboard connected and
is detected in device manager as my keyboard. the USB keyboard is detected
as HID keyboard device. the program finds the keyboard if it is attached.
and I am getting valid handles. however, everytime I use the readfile
function I am getting "object reference not set to an instant of an object"
exception. if i use any other function it fails and I am getting -1 in the
"success" parameter. I am including my code:

HidD_GetHidGuid (HidGuid)

'Friend Function FindDeviceFromG uid _

'(ByVal myGuid As System.Guid, _

'ByRef devicePathName( ) As String) _

'As Boolean

'Purpose : Uses SetupDi API functions to retrieve the device path name of an

' : attached device that belongs to an interface class.

'Accepts : myGuid - an interface class GUID.

' : devicePathName - a pointer to an array of strings that will contain

' : the device path names of attached devices.

'Returns : True if at least one device is found, False if not.

'Fill an array with the device path names of all attached HIDs.

DeviceFound = MyDeviceManagem ent.FindDeviceF romGuid _

(HidGuid, _


'If there is at least one HID, attempt to read the Vendor ID and Product ID

'of each device until there is a match or all devices have been examined.

If DeviceFound = True Then

MemberIndex = 0


HIDHandle = CreateFile _

(DevicePathName (MemberIndex), _

0, _


Security, _


0, _



MyHID.DeviceAtt ributes.Size = Marshal.SizeOf( MyHID.DeviceAtt ributes)

Result = HidD_GetAttribu tes(HIDHandle, MyHID.DeviceAtt ributes)

If (Result <> 0) Then

'Find out if the device matches the one we're looking for.

If (MyHID.DeviceAt tributes.Vendor ID = MyVendorID) And _

(MyHID.DeviceAt tributes.Produc tID = MyProductID) Then

MyDeviceDetecte d = True

'Save the DevicePathName so OnDeviceChange( ) knows which name is my device.

MyDevicePathNam e = DevicePathName( MemberIndex)


'It's not a match, so close the handle.

MyDeviceDetecte d = False

Result = CloseHandle(HID Handle)

End If


'There was a problem in retrieving the information.

MyDeviceDetecte d = False

Result = CloseHandle(HID Handle)

End If

End If

'Keep looking until we find the device or there are no more left to examine.

MemberIndex = MemberIndex + 1

Loop Until ((MyDeviceDetec ted = True) Or _

(MemberIndex = UBound(DevicePa thName) + 1))

If MyDeviceDetecte d Then

rtbstatus.Text = rtbstatus.Text + vbCrLf + "keyboard found"

'The device was detected.

'Register to receive notifications if the device is removed or attached.

Success = MyDeviceManagem ent.RegisterFor DeviceNotificat ions _

(MyDevicePathNa me, _

Me.Handle, _

HidGuid, _

DeviceNotificat ionHandle)
'Debug.WriteLin e("RegisterForD eviceNotificati ons = " & Success)

'Learn the capabilities of the device.

MyHID.Capabilit ies = MyHID.GetDevice Capabilities _


If Success Then

'Get and display the Input report buffer size.

'GetInputReport BufferSize()

rtbstatus.Text = rtbstatus.Text + vbCrLf + "register notification is set"

'************** *************** **

ReadHandle = CreateFile _

(MyDevicePathNa me, _


0, _

Security, _


0, _

0) I also tried it with overlaping. nogo

rtbstatus.Text = rtbstatus.Text + vbCrLf + "handle created"


'Flush any waiting reports in the input buffer.

MyHID.FlushQueu e(ReadHandle)

MyHID.FlushQueu e(HIDHandle)

'************** *************** ************

'start reading

Dim InputReportBuff er() As Byte

Dim NumberOfBytesRe ad As Long

ReDim InputReportBuff er(32)

success = HidD_GetFeature _

(hidHandle, _

InputReportBuff er(0), _

CInt(UBound(inF eatureReportBuf fer) + 1))

'sucess always = false and input report buffer = 0s. I also tried

HidD_GetInputRe port and read file functions. nogo.

any idea what i am doing wrong? any input is appreciated.

Nov 21 '05 #1
0 6679

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