我正在研究一个经典的asp项目，该项目需要将字符串发送到DLL，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DLL并使用 regasm 和 / codebase 进行了注册，这使得IIS能够识别它。
虽然我可以使用 Server.CreateObject（“ MyDLL”）设置对象，但不会出错，但尝试访问其中的C＃方法时遇到麻烦。
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，我尝试按以下方式访问 SendStringToPrinter 方法：
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。
重要的是要告知所有访问DLL的权限都已授予，并且如果我在Visual Studio 2015上启动新的VB项目并添加我的自定义DLL作为参考，那么它就像一个超级按钮一样起作用。
真正的问题是：是否可以做我正在尝试的事情？
编辑
在评论中与一些成员讨论之后，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 。 如我之前所说，如果我在Windows应用程序上使用此DLL，它可以正常工作，但在ASP上却不能。 我现在知道问题出在哪里，但我不知道如何解决。
答案 0 :(得分：1)
经过大量研究和夜幕降临时，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。
我们去看代码：
首先，我去AssemblyInfo.cs并更改了[assembly: ComVisible(false)]，在每个类都想对 COM 可见之前，我添加了[ComVisible(true)]此MSDN文档：https://msdn.microsoft.com/en-us/library/ms182198.aspx
这之后是我最困难的部分：将静态方法转换为实例方法。
但是，进一步研究并尝试不遗余力，我将代码从以下位置更改：
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);
}
}
收件人：
[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);
}
}
此后一切顺利，我能够如下调用该方法：
set objZebra = Server.CreateObject("PrintZebra.RawPrinterHelper")
objZebra.SendStringToPrinter strPrinterName, strText
就是这样。希望这可以解决与我的问题几乎相同的任何其他问题。