Waylander1970
asked on
Calling COM interface without type library
Hi all,
I have a COM interface (the Still Image Aquisition library in sti.dll) that I need to call from VB.
My test code so far is;
Private Const STI_VERSION = &H2
Private Declare Function GetModuleHandle Lib "kernel32" Alias "GetModuleHandleA" _
(ByVal lpModuleName As String) As Long
Private Declare Function StiCreateInstance Lib "sti.dll" Alias "StiCreateInstanceA" _
(ByVal hInst As Long, _
ByVal dwVer As Long, _
ByVal ppSti As Long, _
ByVal punkOuter As Long _
) As Long
Private Declare Sub CopyMemory Lib "kernel32" _
Alias "RtlMoveMemory" _
(lpvDest As Any, _
lpvSource As Any, _
ByVal cbCopy As Long)
Private Sub Command2_Click()
Dim lRet As Long
Dim lProcessHandle As Long
Dim dwVer As Long
Dim oTemp As Object
Dim ppSti As Object
Dim lPointerToInterface As Long
Dim pwszDeviceName As String ' LPWSTR
Dim pdwEventCode As Long ' DWORD
Dim pwszEventName As String ' LPWSTR
' The following is required for design time.
lProcessHandle = GetModuleHandle("vb6.exe" & Chr(0))
If (lProcessHandle = 0) Then
' Must be in run time.
lProcessHandle = GetModuleHandle(App.EXENam e & ".exe" & Chr(0))
End If
dwVer = STI_VERSION
lRet = StiCreateInstance(lProcess Handle, dwVer, VarPtr(lPointerToInterface ), 0&)
If (lRet = 0) Then
' Turn the pointer into an illegal, uncounted interface
CopyMemory oTemp, (lPointerToInterface), 4
' Call AddRef method, so that ppSti becomes a legal reference.
Set ppSti = oTemp
' Destroy the illegal reference by setting it to Nothing without calling Release.
CopyMemory oTemp, 0&, 4
' We now have an STI object available to call methods on.
pwszDeviceName = String(1024, Chr(0))
pwszEventName = String(1024, Chr(0))
pdwEventCode = 0
lRet = ppSti.GetSTILaunchInformat ion(pwszDe viceName, pdwEventCode, pwszEventName)
End If
End Sub
The first CopyMemory call fails, I am not passing a correct pointer somehow. The StiCreateInstance call required a pointer to a pointer where it would store the COM interface pointer. This call succeeds and I am trying to make use of that pointer by converting it into a generic object.
I am nearly there with this, but get a problem when copying pointers. I think that there may be more problems ahead because the functions are not strongly prototyped.
Is this the way to go or are there better ways of accessing this interface? For example, should I attempt to translate the C++ interface to a VB type library (never done this before) and use that? As far as I can see, no one else has a type library for this.
Hope someone can help.
Regards
Ryan
I have a COM interface (the Still Image Aquisition library in sti.dll) that I need to call from VB.
My test code so far is;
Private Const STI_VERSION = &H2
Private Declare Function GetModuleHandle Lib "kernel32" Alias "GetModuleHandleA" _
(ByVal lpModuleName As String) As Long
Private Declare Function StiCreateInstance Lib "sti.dll" Alias "StiCreateInstanceA" _
(ByVal hInst As Long, _
ByVal dwVer As Long, _
ByVal ppSti As Long, _
ByVal punkOuter As Long _
) As Long
Private Declare Sub CopyMemory Lib "kernel32" _
Alias "RtlMoveMemory" _
(lpvDest As Any, _
lpvSource As Any, _
ByVal cbCopy As Long)
Private Sub Command2_Click()
Dim lRet As Long
Dim lProcessHandle As Long
Dim dwVer As Long
Dim oTemp As Object
Dim ppSti As Object
Dim lPointerToInterface As Long
Dim pwszDeviceName As String ' LPWSTR
Dim pdwEventCode As Long ' DWORD
Dim pwszEventName As String ' LPWSTR
' The following is required for design time.
lProcessHandle = GetModuleHandle("vb6.exe" & Chr(0))
If (lProcessHandle = 0) Then
' Must be in run time.
lProcessHandle = GetModuleHandle(App.EXENam
End If
dwVer = STI_VERSION
lRet = StiCreateInstance(lProcess
If (lRet = 0) Then
' Turn the pointer into an illegal, uncounted interface
CopyMemory oTemp, (lPointerToInterface), 4
' Call AddRef method, so that ppSti becomes a legal reference.
Set ppSti = oTemp
' Destroy the illegal reference by setting it to Nothing without calling Release.
CopyMemory oTemp, 0&, 4
' We now have an STI object available to call methods on.
pwszDeviceName = String(1024, Chr(0))
pwszEventName = String(1024, Chr(0))
pdwEventCode = 0
lRet = ppSti.GetSTILaunchInformat
End If
End Sub
The first CopyMemory call fails, I am not passing a correct pointer somehow. The StiCreateInstance call required a pointer to a pointer where it would store the COM interface pointer. This call succeeds and I am trying to make use of that pointer by converting it into a generic object.
I am nearly there with this, but get a problem when copying pointers. I think that there may be more problems ahead because the functions are not strongly prototyped.
Is this the way to go or are there better ways of accessing this interface? For example, should I attempt to translate the C++ interface to a VB type library (never done this before) and use that? As far as I can see, no one else has a type library for this.
Hope someone can help.
Regards
Ryan
ASKER
Thanks Azra,
I'm familiar with Eduardo's work, but I cannot see any help on his page on how to actually do it.
With the other link, it redirects to a missing page.
Do you have any more specific examples or alternative links?
Ryan
I'm familiar with Eduardo's work, but I cannot see any help on his page on how to actually do it.
With the other link, it redirects to a missing page.
Do you have any more specific examples or alternative links?
Ryan
ASKER CERTIFIED SOLUTION
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ASKER
You have been very helpful, although I was rather hoping for a small example here. Does anyone else have any examples of this?
I'm willing to close this and award to Azra (for his politeness and helpful attitude more than the answer I needed) unless someone else would like to contribute.
I'm willing to close this and award to Azra (for his politeness and helpful attitude more than the answer I needed) unless someone else would like to contribute.
ASKER
Although accurate and very knowledgable, I was after an example.
Yes. You can get good references on how this might be done by looking at the type library done here (translation of over 100 interfaces):
http://www.domaindlx.com/e_morcillo/scripts/type/default.asp
This article also discusses the creation of type libraries, not directly from a C++ interface, but the information should be useful:
http://www.vbbyjc.com/articles/vbtoidl.htm