Find HID Devices C#

Question

I need to connect to a USB-device connected to the computer, I have looked around a bit and found some example projects, but cant get this to work. Everything runs nice, but I don't even get into the while-function. Since SetupDiGetClassDevs is from the setupapi.dll I can't debug this function. I do have devices connected, so that is not my problem. Also hInfoSet does get size = 8.

public static HIDDevice FindDevice(int nVid, int nPid, Type oType)
{
 string strPath = string.Empty;
 string strSearch = string.Format("vid_{0:x4}&pid_{1:x4}", nVid, nPid); // first, build the path search string
 Guid gHid;
 HidD_GetHidGuid(out gHid); // next, get the GUID from Windows that it uses to represent the HID USB interface
 IntPtr hInfoSet = SetupDiGetClassDevs(ref gHid, null, IntPtr.Zero, DIGCF_DEVICEINTERFACE | DIGCF_PRESENT); // this gets a list of all HID devices currently connected to the computer (InfoSet)
 try
 {
 DeviceInterfaceData oInterface = new DeviceInterfaceData(); // build up a device interface data block
 oInterface.Size = Marshal.SizeOf(oInterface);
 // Now iterate through the InfoSet memory block assigned within Windows in the call to SetupDiGetClassDevs
 // to get device details for each device connected
 int nIndex = 0;
 while (SetupDiEnumDeviceInterfaces(hInfoSet, 0, ref gHid, (uint)nIndex, ref oInterface)) // this gets the device interface information for a device at index 'nIndex' in the memory block
 {
 string strDevicePath = GetDevicePath(hInfoSet, ref oInterface); // get the device path (see helper method 'GetDevicePath')
 if (strDevicePath.IndexOf(strSearch) >= 0) // do a string search, if we find the VID/PID string then we found our device!
 {
 HIDDevice oNewDevice = (HIDDevice)Activator.CreateInstance(oType); // create an instance of the class for this device
 oNewDevice.Initialise(strDevicePath); // initialise it with the device path
 return oNewDevice; // and return it
 }
 nIndex++; // if we get here, we didn't find our device. So move on to the next one.
 }
 }
 finally
 {
 // Before we go, we have to free up the InfoSet memory reserved by SetupDiGetClassDevs
 SetupDiDestroyDeviceInfoList(hInfoSet);
 }
 return null; 
}

Answer 1

Have you tried calling Marshal.GetLastWin32Error and printing the value after the while loop if it's not entering? Make sure to enable SetLastError on SetupDiEnumDeviceInterfaces.

Afterwards, lookup your error code here: http://msdn.microsoft.com/en-us/library/windows/desktop/ms681381%28v=vs.85%29.aspx

EDIT - After reading your comment, the structure should look something like this:

[StructLayout(LayoutKind.Sequential)]
struct GUID
{
 public int a;
 public short b;
 public short c;
 [MarshalAs(UnmanagedType.ByValArray, SizeConst=8)]
 public byte[] d;
}
[StructLayout(LayoutKind.Sequential)]
struct SP_DEVICE_INTERFACE_DATA
{
 public uint cbSize;
 public GUID InterfaceClassGuid;
 public uint Flags;
 public IntPtr Reserved;
}

• Nick3: Thanks! I tryed this now, and got "1784: The supplied user buffer is not valid for the requested operation". But I'm still not sure how to fix this, do you have any idea why this error occures?
• master131: My guess is that your "DeviceInterfaceData" structure is not marshalled correctly (Marshal.SizeOf is returning the wrong size). Check my edited post.