从经典 ASP 调用 .Net C# DLL 方法

Question

我正在处理一个经典的 asp 项目，该项目需要将一个字符串发送到一个 DLL，该 DLL 将对其进行序列化并发送到 Zebra 热敏打印机。

我已经构建了我的 DLL 并使用regasm和/codebase注册了它，这使 IIS 能够识别它。

虽然我可以使用Server.CreateObject("MyDLL")设置我的对象而没有错误，但我在尝试访问其中的 C# 方法时遇到了麻烦。

DLL 的 C# 代码编写如下：

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;
        }            

    }
}

在我的 ASP 应用程序中，我试图访问SendStringToPrinter方法，如下所示：

Dim objZebra    
set objZebra = Server.CreateObject("Opus127Etiquetas.RawPrinterHelper")

objZebra.SendStringToPrinter

但是调试器说 objZebra 不支持SendStringToPrinter属性或方法。

重要的是要告诉访问 DLL 的所有权限都已授予，如果我在 Visual Studio 2015 上启动一个新的 VB 项目，添加我的自定义 DLL 作为参考，它就像一个魅力。

真正的问题是：有可能做我正在尝试的事情吗？

编辑

在评论中与一些成员讨论后，我意识到我真正需要知道的是如何将上面的 C# 方法从static更改为instance。正如我之前所说，如果我在 Windows 应用程序上使用这个 DLL，它可以正常工作，但在 ASP 上却没有。我现在知道问题是什么，但我不知道如何解决它。

Answer 1

经过大量的研究和熬夜，我意识到我的代码出了什么问题。

首先，我要感谢 @Lankymart 和 @SLaks 为我指明方向。

让我们进入代码：

首先，我去AssemblyInfo.cs更改了[assembly: ComVisible(false)]，在我希望对COM可见的每个类之前，我添加[ComVisible(true)]了我在此 MSDN 文档中找到的内容：https : //msdn.microsoft.com/en-us/library/ms182198.aspx

之后对我来说是最困难的部分：将静态方法转换为实例方法。

但是，进一步研究并尝试不放弃，我改变了我的代码：

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);
    }
}

到：

[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);
    }
}

之后一切顺利，我可以按如下方式调用该方法：

set objZebra = Server.CreateObject("PrintZebra.RawPrinterHelper")   
objZebra.SendStringToPrinter strPrinterName, strText

就是这样。希望这可以帮助与我的问题几乎或相同的任何其他人。