Convert forms to API C#

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I am trying to convert c# forums application to a windows service api so that I can interact from browser.

.NET TWAIN image scanner[^]
I am complete beginner in c# and twain technology so I want to first rewrite the library in c# console then make it api/ windows service.

But I faced major roadblock and not sure how to convert this into c# console or api app
In the source code

public void Init( IntPtr hwndp )
		{
		Finish();
		TwRC rc = DSMparent( appid, IntPtr.Zero, TwDG.Control, TwDAT.Parent, TwMSG.OpenDSM, ref hwndp );
		if( rc == TwRC.Success )
			{
			rc = DSMident( appid, IntPtr.Zero, TwDG.Control, TwDAT.Identity, TwMSG.GetDefault, srcds );
			if( rc == TwRC.Success )
				hwnd = hwndp;
			else
				rc = DSMparent( appid, IntPtr.Zero, TwDG.Control, TwDAT.Parent, TwMSG.CloseDSM, ref hwndp );
			}
		}

Init (this.handle) is used in windows forums but how can I give the input to twain dll if its a console or an api app.

I need to get the dll handle in order to perform any further functions but I am stuck in this step.

I tried giving intptr hwndp= new intptr(x) where 3 is int x=3. Null pointer is resulting in failure. But I believe this is not how you do it. I need to give some variable type so that dll will give me back or populate its value or handle instead of setting it myself.

Anyone plz help I am stuck at this step from past 5 days and not sure how to proceed

What I have tried:

Giving it fixed value into the function

Posted 29-Nov-20 13:30pm

htanmsa id

Updated 29-Nov-20 16:30pm

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Dave Kreskowiak 30-Nov-20 10:51am

It's "Windows Forms", not "forums".

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honey the codewitch · Accepted Answer · 2020-11-29T16:30:00

I don't think you can use TWAIN without a window. You're going to run into that problem in the console and the service. You won't be able to use windows forms but you could P/invoke CreateWindow/CreateWindowEx from User32.dll and perhaps use that.

... inside service or program class:

C#

IntPtr32 _handle;

... inside start up function somewhere

C#

if (string.IsNullOrEmpty(className))
    className = "TwainWindow";
_wndProc = WndProc;


// Create WNDCLASS
var wndclass = new WNDCLASS();
wndclass.lpszClassName = className;
wndclass.lpfnWndProc = _wndProc;

var classAtom = RegisterClassW(ref wndclass);

var lastError = Marshal.GetLastWin32Error();

if (classAtom == 0 && lastError != ERROR_CLASS_ALREADY_EXISTS)
{
    throw new Exception("Could not register window class");
}

// Create window
_handle = CreateWindowExW(
    0,
    wndclass.lpszClassName,
    String.Empty,
    0,
    0,
    0,
    0,
    0,
    IntPtr.Zero,
    IntPtr.Zero,
    IntPtr.Zero,
    IntPtr.Zero
);
}

That should create an invisible window

I didn't post the complete code here because there's quite a bit to it, but you can try using my MessageWindow class to create an invisible hwnd for you.

It's in this code.
Understanding Windows Message Queues for the C# Developer[^]

You'll have to modify the WindowProc (i think it's called) window procedure in that code. I'll bet you a dollar TWAIN will send special messages to that routine which you'll treat as TWAIN "events" and process them. If it doesn't do that then the TWAIN libraries themselves create a UI and you are out of luck.

I haven't tested the idea within the service: Usually to create *visible* windows you must allow your service to interact with the desktop. I *think* invisible windows are fine.