从 ASP 到 .NET COM 的方法调用失败

Question

背景：

我有一个用 ASP (VBScript) 编写的遗留应用程序，它调用用 VB6 编写的 COM 组件。我们正在分阶段升级，需要先将 COM 组件更新为 .NET，同时保持与 ASP 的互操作性。

情况：

1. 我创建了一个示例 .NET 类，并根据 MSDN 文档使用各种属性将其公开给 COM 系统
2. 我可以实例化类
3. 我可以在类上调用所需的方法

问题：

1. 参数值未发送到 COM 方法。例如所有数字类型在方法内都有值 0；所有引用类型在方法内都有空值。文字字符串被正确地传递给方法。但是，不传递字符串变量。
2. 返回值同样的问题。无论方法返回什么值，ASP 上的变量都有默认值（0 或 null 视情况而定）。

COM 代码

<ComVisible(True)>
<InterfaceType(ComInterfaceType.InterfaceIsIDispatch)>
Public Interface IClass1
    Function Triple(ByVal input As String) As Integer
End Interface

<ComVisible(True)>
<ProgId("TESTCOM.Class1")>
<ClassInterface(ClassInterfaceType.None)>
Public Class Class1
    Inherits ServicedComponent
    Implements IClass1

    Public Sub New()
        ' needed for COM
    End Sub

    Public Function Triple(input As String) As Integer Implements IClass1.Triple
        IO.File.WriteAllText("C:\TestCOM.Class1_Triple.log", String.Format("[{0:s}] Input: {1}", Date.Now, input)) ''' this file is updated; so I know method is being called.
        Return 97
    End Function
End Class

备用 COM 代码

<ComVisible(True)>
<ProgId("TESTCOM.Class1")>
<ComClass("E26FE8A0-8AC7-4824-9776-30ECDD473AA3")>
Public Class Class1
    'Inherits ServicedComponent
    'Implements IClass1

    Public Sub New()
        ' needed for COM
    End Sub

    Private Const LogMessageFormat As String = "[{0:s}] Input: {1}, {2}" + vbCrLf

    Public Function Triple(csinput As String, nInput As Integer) As Integer 'Implements IClass1.Triple
        IO.File.AppendAllText("C:\TestCOM.Class1_Triple.log", 
                              String.Format(LogMessageFormat, Date.Now, if(csinput isnot Nothing, csinput, "**NULL**"), nInput))
        Return 97
    End Function
End Class

ASP 代码

dim testNETCOM 
set testNETCOM = Server.CreateObject("TESTCOM.Class1")

' ** use this to check if there was any error during instantiation    
If Err.Number <> 0 Then
   Response.Redirect("http://"&Err.Description&"/")
  'Response.Write (Err.Description& "<br><br>")
else
    'Response.Redirect("http://no-error/")
End If
' ** use this to check if object is actually instantiated
if testNETCOM is nothing then
    Response.Redirect("http://no-com/")
else
    'Response.Redirect("http://yes-com/")
end if

dim nInput
set nInput = 41

dim nOutput
set nOutput = -1
set nOutput = CLng(testNETCOM.Triple("test message")) ' this string is received in the method
set nOutput = CLng(testNETCOM.Triple(CStr(nInput)))   ' this string is not received in the method

' ** use this to check if return value is what we expected
if nOutput <> 0 then
    Response.Redirect("http://test/")
else
    Response.Redirect("http://notest/") ''' **this happens**
end if

Answer 1

问题在于 ASP 的语法

1. 对于简单的数据类型，不要使用'set'
2. 对于对象，使用'set'

因为我是对简单类型使用set，所以在赋值过程中出现了错误，变量的值为null/nothing/empty。

set nInput = 41 ' this is wrong
nInput = 41     ' this is right
set nOutput = CLng(testNETCOM.Triple(CStr(nInput))) ' this is wrong
nOutput = CLng(testNETCOM.Triple(CStr(nInput)))     ' this is right

Answer 2

试一试：

<ComVisible(True)> 
<Guid("79571A9D-2345-48D9-8F86-7F6761A97DBA")>
<InterfaceType(ComInterfaceType.InterfaceIsIDispatch)>
Public Interface IClass1
    Function Triple(ByVal input As String) As Integer
End Interface

<ComVisible(True)>
<Guid("E26FE8A0-8AC7-4824-9776-30ECDD473AA3")>
<ProgId("TESTCOM.Class1")>
<ClassInterface(ClassInterfaceType.None)>
Public Class Class1
    Inherits ServicedComponent
    Implements IClass1

    Public Sub New()
        ' needed for COM
    End Sub

    Public Function Triple(input As String) As Integer Implements IClass1.Triple
        IO.File.WriteAllText("C:\TestCOM.Class1_Triple.log", String.Format("[{0:s}] Input: {1}", Date.Now, input)) ''' this file is updated; so I know method is being called.
        Return 97
    End Function
End Class

或者：

<ComVisible(True)>
<ProgId("TESTCOM.Class1")>
<ComClass("E26FE8A0-8AC7-4824-9776-30ECDD473AA3", "79571A9D-2345-48D9-8F86-7F6761A97DBA")>
Public Class Class1
    'Inherits ServicedComponent
    'Implements IClass1

    Public Sub New()
        ' needed for COM
    End Sub

    Private Const LogMessageFormat As String = "[{0:s}] Input: {1}, {2}" + vbCrLf

    Public Function Triple(csinput As String, nInput As Integer) As Integer 'Implements IClass1.Triple
        IO.File.AppendAllText("C:\TestCOM.Class1_Triple.log", 
                              String.Format(LogMessageFormat, Date.Now, if(csinput isnot Nothing, csinput, "**NULL**"), nInput))
        Return 97
    End Function
End Class