[RESOLVED] How to use LoadLibrary()/GetProcAddress()?

Hey -

The following code works great to interface *.dll that I built in Ada from VB.NET (2008) ...

Private Declare Function TestDelegate Lib "C:\ABC.dll" Alias "Test" _
(ByVal A As Single, _
ByVal B As Integer, _
ByVal C As String, _
ByRef D As TestType) As Single

... where TestType is a struct. The only problem I have with this is that the *.dll and its path has to be hard coded.

So I started looking at using LoadLibrary() and GetProcAddress(). I figured out the following interfaces ...

<DllImport("kernel32.dll", CharSet:=CharSet.Auto, SetLastError:=True)> _
Public Function LoadLibrary(<[In](), MarshalAs(UnmanagedType.LPTStr)> ByVal lpFileName As String) As IntPtr
End Function

<DllImport("kernel32.dll", CharSet:=CharSet.Auto, ExactSpelling:=True)> _
Public Function GetProcAddress(<[In]()> ByVal hModule As IntPtr, <[In](), MarshalAs(UnmanagedType.LPStr)> ByVal lpProcName As String) As IntPtr
End Function

... that I can call like ...

Dim lLibraryHandle As IntPtr = LoadLibrary("C:\ABC.dll")
Dim lFunctionHandle As IntPtr = GetProcAddress(lLibraryHandle, "Test")

I check for IntPtr.Zero to make sure this all worked but now the question is how can I actually use the lFunctionHandle to call Test()? Has somebody worked
with this before?

I'm also curious what the difference is between the <DllImport("kernel32.dll" ... and something like Private Declare Function ABC Lib "kernel32" (...) As XYZ to interface a *.dll?

My last question is whether it is necessary to call FreeLibrary() or whether VB will handle freeing up the memory?

Thanks,
Joe

After a quick search I found this:
http://www.codeproject.com/KB/cs/dyninvok.aspx

You seem to have to use "InvokeFunc" API to do what you want:

Code:

---

<DllImport("Invoke", CharSet:=CharSet.Unicode)]
Public Shared Function InvokeFunc(ByVal funcptr As IntPtr, ByVal hwnd As IntPtr, ByVal message As String, ByVal title As String, ByVal flags As Integer) As Integer

---

And yes it is wise to call FreeLibrary, since it frees the resources so other programs (including Windows for file move/delete/rename) can access the files.

Yeah ... most examples I found were in C# but I finally came across something that uses the Invoke() as you suggested ...

http://msdn.microsoft.com/en-us/libr...er(VS.80).aspx

I started to play with this and it looks very promosing ... thanks!

Joe

One cool related project is the P/Invoke Interop Assistant.

Hey -

I installed the PInvoke Interop Assistant but it will not work with the *.dll as it does not have an asssembly manifest.

Joe

That's right. I was referring to the PInvoke functionality which can help you figure out the method signature in C# and VB.Net.

Nice tool and I will definitely keep it in mind next time I run into a similar problem. As to my current problem, I actually figured out how to make it work:

The problem was with the "CharSet.Unicode" in ...

<UnmanagedFunctionPointer(CallingConvention.StdCall, CharSet:=CharSet.Unicode)> _
Delegate Function XYZ ...

... I guess the Ada *.dll was not happy about the String being passed in four times the size it expected. I changed that to "CharSet.Ansi" and it is now working beautifully!

Thanks!
Joe