I'm working on a classic asp project that needs to send a string to a DLL who will serialize it and send to a Zebra Thermal Printer.
I have already build my DLL and registered it using regasm followed by /codebase which make IIS recognizes it.
Althougt I'm able to set my object with Server.CreateObject("MyDLL") without errors, I'm having trouble trying to access the C# methods in it.
The C# code for the DLL was written as below:
using System;
using System.Runtime.InteropServices;
using System.IO;
//[assembly: ComVisible(true)]
//[assembly: Guid("6c87161d-1e02-40ef-8512-82f30bc1ae3e")]
namespace PrintZebra
{
//[ClassInterface(ClassInterfaceType.None)]
/// <summary>
/// Classe
/// </summary>
public class RawPrinterHelper
{
// Structure and API declarions:
/// <summary>
///
/// </summary>
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public class DOCINFOA
{
[MarshalAs(UnmanagedType.LPStr)] public string pDocName;
[MarshalAs(UnmanagedType.LPStr)] public string pOutputFile;
[MarshalAs(UnmanagedType.LPStr)] public string pDataType;
}
[DllImport("winspool.Drv", EntryPoint = "OpenPrinterA", SetLastError = true, CharSet = CharSet.Ansi, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool OpenPrinter([MarshalAs(UnmanagedType.LPStr)] string szPrinter, out IntPtr hPrinter, IntPtr pd);
[DllImport("winspool.Drv", EntryPoint = "ClosePrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool ClosePrinter(IntPtr hPrinter);
[DllImport("winspool.Drv", EntryPoint = "StartDocPrinterA", SetLastError = true, CharSet = CharSet.Ansi, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool StartDocPrinter(IntPtr hPrinter, Int32 level, [In, MarshalAs(UnmanagedType.LPStruct)] DOCINFOA di);
[DllImport("winspool.Drv", EntryPoint = "EndDocPrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool EndDocPrinter(IntPtr hPrinter);
[DllImport("winspool.Drv", EntryPoint = "StartPagePrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool StartPagePrinter(IntPtr hPrinter);
[DllImport("winspool.Drv", EntryPoint = "EndPagePrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool EndPagePrinter(IntPtr hPrinter);
[DllImport("winspool.Drv", EntryPoint = "WritePrinter", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
public static extern bool WritePrinter(IntPtr hPrinter, IntPtr pBytes, Int32 dwCount, out Int32 dwWritten);
// SendBytesToPrinter()
// When the function is given a printer name and an unmanaged array
// of bytes, the function sends those bytes to the print queue.
// Returns true on success, false on failure.
public static bool SendBytesToPrinter(string szPrinterName, IntPtr pBytes, Int32 dwCount)
{
Int32 dwError = 0, dwWritten = 0;
IntPtr hPrinter = new IntPtr(0);
DOCINFOA di = new DOCINFOA();
bool bSuccess = false; // Assume failure unless you specifically succeed.
di.pDocName = ".NET RAW Document";
di.pDataType = "RAW";
// Open the printer.
if (OpenPrinter(szPrinterName.Normalize(), out hPrinter, IntPtr.Zero))
{
// Start a document.
if (StartDocPrinter(hPrinter, 1, di))
{
// Start a page.
if (StartPagePrinter(hPrinter))
{
// Write your bytes.
bSuccess = WritePrinter(hPrinter, pBytes, dwCount, out dwWritten);
EndPagePrinter(hPrinter);
}
EndDocPrinter(hPrinter);
}
ClosePrinter(hPrinter);
}
// If you did not succeed, GetLastError may give more information
// about why not.
if (bSuccess == false)
{
dwError = Marshal.GetLastWin32Error();
}
return bSuccess;
}
public static bool SendFileToPrinter(string szPrinterName, string szFileName)
{
// Open the file.
FileStream fs = new FileStream(szFileName, FileMode.Open);
// Create a BinaryReader on the file.
BinaryReader br = new BinaryReader(fs);
// Dim an array of bytes big enough to hold the file's contents.
Byte[] bytes = new Byte[fs.Length];
bool bSuccess = false;
// Your unmanaged pointer.
IntPtr pUnmanagedBytes = new IntPtr(0);
int nLength;
nLength = Convert.ToInt32(fs.Length);
// Read the contents of the file into the array.
bytes = br.ReadBytes(nLength);
// Allocate some unmanaged memory for those bytes.
pUnmanagedBytes = Marshal.AllocCoTaskMem(nLength);
// Copy the managed byte array into the unmanaged array.
Marshal.Copy(bytes, 0, pUnmanagedBytes, nLength);
// Send the unmanaged bytes to the printer.
bSuccess = SendBytesToPrinter(szPrinterName, pUnmanagedBytes, nLength);
// Free the unmanaged memory that you allocated earlier.
Marshal.FreeCoTaskMem(pUnmanagedBytes);
return bSuccess;
}
public static Int32 SendStringToPrinter(string szPrinterName, string szString)
{
IntPtr pBytes;
Int32 dwCount;
// How many characters are in the string?
//dwCount = szString.Length;joao
dwCount = (szString.Length + 1) * Marshal.SystemMaxDBCSCharSize;
// Assume that the printer is expecting ANSI text, and then convert
// the string to ANSI text.
pBytes = Marshal.StringToCoTaskMemAnsi(szString);
// Send the converted ANSI string to the printer.
bool bSuccess = SendBytesToPrinter(szPrinterName, pBytes, dwCount);
Int32 dwError = 0;
if (bSuccess == false)
{
dwError = Marshal.GetLastWin32Error();
}
Marshal.FreeCoTaskMem(pBytes);
return dwError;
}
}
}
In my ASP application I'm trying to access the SendStringToPrinter method as follows:
Dim objZebra
set objZebra = Server.CreateObject("Opus127Etiquetas.RawPrinterHelper")
objZebra.SendStringToPrinter
But debugger says that objZebra does not support SendStringToPrinter property or method.
Is important to tell that all the permissions to access the DLL are granted and if I start a new VB project on Visual Studio 2015 adding my custom DLL as a reference it works like a charm.
The real question is: is it possible to do what I'm trying?
EDIT
After discussing with some members at the comments I realize that what I realy need to know is how to change the C# methods above from static to instance. As I said before, if I use this DLL on a Windows Application it works fine, but on ASP it didn't. I now know what the problem is but I don't know how to solve it.
After lots of research and nights awake, I realized what was wrong with my code.
First I want to thank @Lankymart and @SLaks for point me the way.
Let's go to the Code:
First I went to AssemblyInfo.cs and change the [assembly: ComVisible(false)], and before every class I wanted to be visible to COM I add [ComVisible(true)] which I find in this MSDN document: https://msdn.microsoft.com/en-us/library/ms182198.aspx
After that cames the most difficult part to me: Turn the static method into a instance method.
But, researching further and trying without give away, I changed my code from:
public static Int32 SendStringToPrinter(string szPrinterName, string szString)
{
...
}
public class PrintHandler
{
[MethodImpl(MethodImplOptions.NoInlining)]
public Int32 SendStringToPrinter(string text, string printerName)
{
return RawPrinterHelper.SendStringToPrinter(printerName, text);
}
}
To:
[ComVisible(true)]
public Int32 SendStringToPrinter(string szPrinterName, string szString)
{
...
}
[ComVisible(true)]
public class PrintHandler
{
RawPrinterHelper rph = new RawPrinterHelper();
[MethodImpl(MethodImplOptions.NoInlining)]
[ComVisible(true)]
public Int32 SendStringToPrinter(string text, string printerName)
{
return rph.SendStringToPrinter(printerName, text);
}
}
After that all went well and I was able to call the method as follows:
set objZebra = Server.CreateObject("PrintZebra.RawPrinterHelper")
objZebra.SendStringToPrinter strPrinterName, strText
That's it. Hope this could help any other with a nearly or same problem as mine.