Re: PInvoke Marshalling....

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That's excellent! Thanks for your help.

One last question...

The wParam is a pointer to a API defined structure (containing a Low DWORD
and a High DWORD), how would I cast this back into the same structure I've
written in my C# proxy in the WndProc?


"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:eWDNBtYFIHA.5160@xxxxxxxxxxxxxxxxxxxxxxx
Daniel,

My previous post outlines what you have to do with allocating the
buffer.

When you pass a StringBuilder, the P/Invoke layer creates a buffer of
unmanaged memory, and passes the pointer to that, populated with the
contents of the string builder. Upon return, the P/Invoke layer marshals
the information from that unmanaged buffer back into the StringBuilder,
and disposes of the pointer.

However, this API is holding onto the pointer, so you have to do the
same.

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx

"Daniel Bass" <danREMOVEbass@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:O78SjhYFIHA.4228@xxxxxxxxxxxxxxxxxxxxxxx
Well, kind of...

A little context may help. I'm writing a front end into a driver for a
USB connected imaging scanner.

DeviceHandle is the handle that I keep hold of for the currently
connected device.

The first call I make into the API though, is
[DllImport("Dependencies\\SNAPI.DLL")]
public static extern int SNAPI_Init(IntPtr hwend, IntPtr[]
DeviceHandles, ref int NumDevices);
This basically expects a windows handler, along with a buffer array which
it uses to populate with scanners that are currently attached to the
system.

I've overriden WndProc, and it's correctly getting the message I'd
expect, in this case it's the WM_VERSION message. All I'm trying to do is
initially query the scanner for the firmware version as a simple way of
exchanging data before I get onto imaging and video!

OnConnect type event does this:
int status = 0;
status = DriverProxy.SNAPI_SetVersionBuffer(handle,
_versionBuffer, _versionBuffer.Length);
status = DriverProxy.SNAPI_TransmitVersion(handle);
_versionBuffer is global StringBuilder, and transmit version tells the
scan to please send me the firmware version to the allocated buffer.

In WndProc override:
protected override void WndProc(ref Message m)
{
switch ((uint)m.Msg)
{
case DriverProxy.WM_SWVERSION:
// should now have a _versionbuffer full of grand
stuff
FirmwareVersionLabel.Text = _versionBuffer.ToString();
break;

}
Debug.WriteLineIf(m.Msg > 0x8000 && m.Msg < 0xBFFF, "HIT! " +
m.Msg.ToString());
base.WndProc(ref m);
}

Now I've a label that gets the Firmware version text assigned to it, but
this is currently blank, and can confirm that the WM_SWVERSION message
comes through...

Hope that helps to explain what I'm trying to achieve.
Thanks again.
Dan.


"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote
in message news:OadAbZYFIHA.3716@xxxxxxxxxxxxxxxxxxxxxxx
Daniel,

I was thinking this is a little odd, since the parameter is named
"DeviceHandle" and not indicative that it is a windows handle. If it is
indeed a windows handle you are passing to the method, then you can
override the WndProc method of the control that contains that windows
handle to look for the message sent to you.

You will have to change your API declaration to this:

[DllImport("Dependencies\\SNAPI.DLL", CharSet=CharSet.Ansi)]
public static extern int SNAPI_SetVersionBuffer(IntPtr DeviceHandle,
IntPtr pData, int max_length);

And then call it like this:

// dataBuffer need to be accessible by the override of WndProc as well.
dataBuffer = Marshal.AllocHGlobal(dataBufferLength);

// Make the API call:
SNAPI_SetVersionBuffer(windowHandle, dataBuffer, dataBufferLength);

Then, in your override of WndProc, in the section that handles the
message to the window:

// Get the string.
string data = Marshal.PtrToStringAnsi(dataBuffer);

// Free the memory.
Marshal.FreeHGlobal(dataBuffer);

// Work with the string.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx


"Daniel Bass" <danREMOVEbass@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:O3sK%23VYFIHA.3548@xxxxxxxxxxxxxxxxxxxxxxx

I pass in a handle of the windows into the API as part of an
initialisation call. Could I then just override "WndProc"?

It's doing the latter, and only sending a message when the parameter
has been sent to the buffer. When you say "allocate the memory"
yourself, I'm not sure what you mean. I'll provide the IntPtr
parameter, and according the API manual, I'll have a global buffer
space that I register with the API which should be populated with the
event call... Does that sound feasible?

Thanks for your help and guidance!

"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote in message news:OovEiMYFIHA.5208@xxxxxxxxxxxxxxxxxxxxxxx
Daniel,

Yes, there is. You can create a class which implements the
IMessageFilter interface and then call the AddMessageFilter method on
the Application class, passing your implementation. Then, in the
PreFilterMessage method, you would check for your message.

There might be a more subtle issue here. When the function
returns, is the string already written to? Or is the string written
to when the message is sent to the application? If it is the former,
then the code you have is ok. If it is the latter, you will have to
change your declaration of the unsigned char * parameter to an IntPtr,
and allocate the memory that you need yourself.

Then, in the handler for the message, you will have to manually
marshal the string to managed code using the static methods on the
Marshal class (freeing the memory of course as well).

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx

"Daniel Bass" <danREMOVEbass@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:u%23iPBKYFIHA.4140@xxxxxxxxxxxxxxxxxxxxxxx
Nicholas,

I've just been reading through the API guide, and realised that it
won't pass me back the data in a synchronous manner.

To quote:
"A command function returns immediately to the host application...
After the command is processed, by the scanner, the host application
received a Windows message indicating the command was processed. The
host applicaition provides a message handler for the ack from the
connected device."

Eeek! In .Net, is there a way to listen for messages? I've worked a
little with message maps, but that was way back and have not see this
sort of basic message handling in .net before...

Cheers.
Dan.

"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote in message news:%23Wy5GFYFIHA.5328@xxxxxxxxxxxxxxxxxxxxxxx
Daniel,

Yes, if the API function is going to write to the buffer, then
passing a StringBuilder will cause the data to be marshaled back to
you correctly.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx

"Daniel Bass" <danREMOVEbass@xxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:%23EkQlBYFIHA.1212@xxxxxxxxxxxxxxxxxxxxxxx
Nicholas,

Excellent, thanks for the prompt reply!

pData is a buffer that I create, then pass into the function to
populate. Does the parameter as a StringBuilder marshall this data
correctly?

Thanks.
Dan.

"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote in message news:ecx5T6XFIHA.280@xxxxxxxxxxxxxxxxxxxxxxx
Daniel,

Actually, it's not pretty obvious. In C++, long corresponds to
a 32-bit integer, which in C#, is an int. Also, you should
declare how your strings are marshaled in the DllImport attribute.
All-in-all, your declaration should look like this:

[DllImport("Dependencies\\SNAPI.DLL", CharSet=CharSet.Ansi)]
public static extern int SNAPI_SetVersionBuffer(IntPtr
DeviceHandle, StringBuilder pData, int max_length);

Also, if the pData parameter is not going to be written to by
the API function, you can pass it as a string.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx


"Daniel Bass" <danREMOVEbass@xxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:u83rn0XFIHA.1056@xxxxxxxxxxxxxxxxxxxxxxx
Greetings!

I'm trying to call this method in a c# app...

SNAPIDLL_API int __stdcall SNAPI_SetCapabilitiesBuffer(HANDLE
DeviceHandle, unsigned char *pData, long max_length);

So far I've got this:
[DllImport("Dependencies\\SNAPI.DLL")]
public static extern int SNAPI_SetVersionBuffer(IntPtr
DeviceHandle, StringBuilder pData, long max_length);

Keep getting a PInvokeStackImbalance error and I think it's the
2nd paramter pData because I've referenced the device handler and
the long typedef is pretty obvious.

For the 2nd paramter I've tried the following without success:
byte[]
char[]
string
StringBuilder
[MarshalAs(UnmanagedType.AnsiBStr)] string

HELP!
Thanks.
Dan.





















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