Question

I’m facing a problem importing a DLL on different environments.
I have to check Windows platform and import the third-party DLL that will be placed in C:\Program Files\ (for 32-bit) or C:Program Files (x86)\ (for 64-bit).

Before the code was written like this:

Declare Function RDRCConnect Lib "c:\program files\TP-DLL\RDRCAP32.DLL" (ByVal lpszServerName As String, ByVal lNetConnType As Integer, ByVal lpszParam1 As String, ByVal lpszParam2 As String, ByVal lpszParam3 As String, ByRef lNetConn As Integer, ByRef lNetErr As Integer) As Integer  
Declare Function RDRCDisconnect Lib "c:\program files\TP-DLL\RDRCAP32.DLL" (ByVal lNetConn As Integer, ByRef lNetErr As Integer) As Integer

…and I changed to use attributes:

Private Const CheminDLL As String = "C:\Program Files\TP-DLL\RDRCAP32.DLL"

<System.Runtime.InteropServices.DllImport(CheminDLL)>
Private Shared Function RDRCConnect(ByVal lpszServerName As String, ByVal lNetConnType As Integer, ByVal lpszParam1 As String, ByVal lpszParam2 As String, ByVal lpszParam3 As String, ByRef lNetConn As Integer, ByRef lNetErr As Integer) As Integer
End Function

How can I change the DLL path dinamically in this scenario, once the DLLImport expects a Constant as parameter?

Answer 1

There’s no way to pass anything other than a constant into the attribute, since attributes, by definition are evaluated at compile-time, not at runtime. There may be better alternatives, but one option I can give you would be to create separate imports for each version:

<DllImport("C:\Program Files\TP-DLL\RDRCAP32.DLL", EntryPoint := "RDRCConnect")>
Private Shared Function RDRCConnect32(ByVal lpszServerName As String, ByVal lNetConnType As Integer, ByVal lpszParam1 As String, ByVal lpszParam2 As String, ByVal lpszParam3 As String, ByRef lNetConn As Integer, ByRef lNetErr As Integer) As Integer
End Function

<DllImport("C:\Program Files (x86)\TP-DLL\RDRCAP32.DLL", EntryPoint := "RDRCConnect")>
Private Shared Function RDRCConnect64(ByVal lpszServerName As String, ByVal lNetConnType As Integer, ByVal lpszParam1 As String, ByVal lpszParam2 As String, ByVal lpszParam3 As String, ByRef lNetConn As Integer, ByRef lNetErr As Integer) As Integer
End Function

Then you would need to choose which one to call appropriately each time you call the method.