I’ve progressed somewhat in my recent efforts with regards to utilizing a virtual channel between receiver and the VDA. I’ve converted the driver to C++ which makes utilizing C-type syntax easier – I can declare variables and assign them in between the code for example. Anyway, the real issue I was having right was calling the C/C++ DLL from WPF/C# which establishes the connection to the driver.

So the first time I call the function in the C++ DLL that initiates the connection to the client driver, this all works, do it again and it failed. But I fixed it by doing a little googling: I was doing this from c#:

[DllImport("VDAAPPV.dll", EntryPoint = "SendAndRecieve", SetLastError = true)]
    private static extern int SendAndRecieve(string message, int messageLength, StringBuilder response, int responseLength);

    private void btnCreateVC_Click( object sender, RoutedEventArgs e )
    {
        try
        {
           var sb = new StringBuilder(100);
           SendAndRecieve("Stuart Mathews is a dude","Stuart Mathews is a dude".Length, sb, sb.Capacity);
           Status.Content = sb.ToString();
           MessageBox.Show("Result was " + sb);
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error sendreceive: "+ ex.Message);
        }
    }

The problem was that the DllImport should have been like this:

[DllImport("VDAAPPV.dll", EntryPoint = "SendAndRecieve", SetLastError = true, CharSet = CharSet.Ansi)]
    private static extern int SendAndRecieve(string message, int messageLength, StringBuilder response, int responseLength);

Note the CharSet = CharSet.Ansi part. Thats because the C function looks like this:

extern "C" EXPORT_ME int SendAndRecieve(const char* message, int messageLength, char* responseBuf, int responseLength)
{
...
}

A pointer to a char is ANSI. Because I’m a fool, I forgot about this for a full day. Anyway, the results are that I can send a message to receiver from the VDA and get a response:

And that’s probably the most important step in working with the Citrix Virtual Channel SDK.

So onwards and upwards!