Marshal error when RegisterStreamReadCallback - c++

Question

I'm using C# to call methods from an dll file to record video.
This is the Marshal methods file
http://pastebin.com/YrVvBfZ9
This is my CameraUtilities file
http://pastebin.com/0AZNtnhk
This is my camera file
http://pastebin.com/ZE3HD1zq
When I call StartRecord method (in camera file) to start Record video.
public void StartRecord()
{
if (this.ListCameras != null)
{
bool bRes = true;
try
{
int tmpError = -1;
m_tmpContext = new IntPtr();
m_handle = new GCHandle();
m_callBackChannels = new ulong[m_ListCameras.Length];
for (int i = 0; i < m_ListCameras.Length; i++)
{
m_callBackChannels[i] = 10;
cameraCurrentIndex = 0;
IntPtr channelHandle = T1800.T18_ChannelOpen(cameraCurrentIndex);
m_ListCameras[cameraCurrentIndex].ChannelHandle = channelHandle;
T1800.T18_CaptureIFrame(m_ListCameras[i].ChannelHandle);
m_ListCameras[i].BeginRecord();
if (AllowRecordVideo)
{
m_del = new T1800.STREAM_READ_CALLBACK(StreamReadCallBack);
m_tmpContext = m_ListCameras[i].ChannelHandle;
tmpError = T1800.T18_RegisterStreamReadCallback(m_del, ref m_tmpContext);
}
}
if (tmpError == -1) bRes = false;
}
catch (Exception ex)
{
Log.Logger.Error(ex);
bRes = false;
}
}
}
It throw an exception
- System.Runtime.InteropServices.MarshalDirectiveException: Invalid PInvoke calling convention.
Thiscall requires that the first parameter is present and can be enregistered.
at System.Runtime.InteropServices.Marshal.GetFunctionPointerForDelegateInternal(Delegate d)
at System.Runtime.InteropServices.Marshal.GetFunctionPointerForDelegate(Delegate d)
at TH.Parking.Wrapper.HBCamera.T1800.dll_T18_RegisterStreamReadCallback(STREAM_READ_CALLBACK STREAM_READ_CALLBACK, IntPtr& context)
at TH.Parking.Wrapper.HBCamera.CameraUtilities.StartRecord() in d:\TH.Parking\TH.Parking\Wrapper\HBCamera\CameraUtilities.cs:line 93
I can't find any reason for this error. Can somebody help me to fix this.

Answer 1

I think the callback you pass to create the STREAM_READ_CALLBACK object should be static. Otherwise, the thispointer is lost during the marshalling.
Instead of:
private int StreamReadCallBack(ulong channelHandle, IntPtr context)
{
...
}
try:
private static int StreamReadCallBack(ulong channelHandle, IntPtr context)
{
...
}
And you'll need to somehow put your instance of CameraUtility into the context parameter.