I am re-writing an MS VC++ 6.0 application in Visual Studio 2005
VB.NET. In order for my new application to communicate with some
hardware (an RFID reader) I need to communicate with a DLL that was
written in MS VC++ 6.0. I have found some excellent discussions that
have helped me define the structures to marshal the data between the
unmanaged and managed code. My problem is that my application is not
working correctly. The result is that the program suddenly quits
without any indication of why.
The flow of the code is this: Initialize the DLL, Ask the DLL to
discover all available RFID readers, The DLL will then "callback" my
application when anything significant occurs (such as an RFID tag is
read).
I wrapped the DLL in a class called RFIDReaderClass . To reduce
bandwidth I have only included a partial class definition here. I can
call all the methods of the DLL without any errors.
My test application is a form with a list view. Whenever a callback is
made the list view is updated with some information using an
"Invoke" call to a method that adds an item to the list view. When
I run the application, in the debugger, I can see a few messages
displayed in the list view then suddenly the program goes away. No
error messages are displayed and I am able to "start debugging"
again.
I suspect that this may be a garbage collection issue but I am stumped.
I have tried KeepAlive and GCHandle.Alloc without success, but I am
probably making the calls incorrectly.
By the way, if I don't register the callback using
RFIDRegisterCal lback method of the DLL then the program doesn't
disappear and seems to run correctly. Unfortunately I need to register
the callback in order to do any useful processing in my application.
Here is the RFIDReaderClass .vb
----------------------------------------------------------------------------------------
Imports System.Runtime. InteropServices
<StructLayout(L ayoutKind.Seque ntial, CharSet:=CharSe t.Ansi)> _
Public Structure RFIDInitStructu re
Public MaximumNumberOf Readers As Integer
Public TagSerialNumber Length As Integer
Public TagMemorySize As Integer
Public BoardInfoFile As String
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure ReaderLocationS tructure
Public ReaderNumber As Integer
Public ChipIndex As Integer
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure ReaderLocationA rray
<MarshalAs(Unma nagedType.ByVal Array, SizeConst:=500) > _
Public vals As ReaderLocationS tructure()
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure TagSerialNumber Structure
<MarshalAs(Unma nagedType.ByVal Array, SizeConst:=9)> _
Public Bytes As System.Byte()
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure TagDataStructur e
<MarshalAs(Unma nagedType.ByVal Array, SizeConst:=1025 )> _
Public Bytes As System.Byte()
End Structure
Public Delegate Sub CallbackDelegat e( _
ByVal ReaderLocation As ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Public Class RFIDReaderClass
Public Declare Function RFIDRegisterCal lback Lib "rfidreader.dll " _
(ByVal AddressOfSub As CallbackDelegat e) As Integer
Public Declare Function RFIDDllInitiali ze Lib "rfidreader.dll " _
(ByRef InitData As RFIDInitStructu re) As Integer
Public Declare Function RFIDDiscoverRea ders Lib "rfidreader.dll " _
(ByRef ReaderLocations As ReaderLocationA rray, _
ByRef NumberOfReaders Found As Integer) As Integer
End Class
----------------------------------------------------------------------------------------
Here is the Form1.vb
----------------------------------------------------------------------------------------
Imports System.Runtime. InteropServices
Public Class Form1
Dim RFIDReader As RFIDReaderClass
Dim RFIDCallbackFun ction As New CallbackDelegat e(AddressOf
RFIDReaderCallb ack)
Dim NumberOfReaders Found As Integer
Dim ReaderLocations As ReaderLocationA rray
Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load
Dim InitData As RFIDInitStructu re
InitData.Maximu mNumberOfReader s = 111
InitData.TagMem orySize = 1024
InitData.TagSer ialNumberLength = 8
InitData.BoardI nfoFile = "c:/NTcommgr.csv"
Dim Result As Integer
Result = RFIDReader.RFID RegisterCallbac k(RFIDCallbackF unction)
Result = RFIDReader.RFID DllInitialize(I nitData)
Result = RFIDReader.RFID DiscoverReaders (ReaderLocation s,
NumberOfReaders Found)
End Sub
Private Sub RFIDReaderCallb ack(ByVal ReaderLocation As
ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Dim d As New updateLabel(Add ressOf updateLabelHand ler)
Me.Invoke(d, New Object() {ReaderLocation , ReaderStatus,
TagSerialNumber , TagData})
End Sub
Private Delegate Sub updateLabel(ByV al ReaderLocation As
ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Private Sub updateLabelHand ler(ByVal ReaderLocation As
ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Dim DisplayString As String
DisplayString = Now.ToShortTime String() & " Slot " & _
ReaderLocation. ReaderNumber.To String() & _
" Index " & ReaderLocation. ChipIndex.ToStr ing() & _
" Status " & ReaderStatus.To String()
DisplayListBox. Items.Add(Displ ayString)
End Sub
Protected Overrides Sub Finalize()
MyBase.Finalize ()
End Sub
End Class
VB.NET. In order for my new application to communicate with some
hardware (an RFID reader) I need to communicate with a DLL that was
written in MS VC++ 6.0. I have found some excellent discussions that
have helped me define the structures to marshal the data between the
unmanaged and managed code. My problem is that my application is not
working correctly. The result is that the program suddenly quits
without any indication of why.
The flow of the code is this: Initialize the DLL, Ask the DLL to
discover all available RFID readers, The DLL will then "callback" my
application when anything significant occurs (such as an RFID tag is
read).
I wrapped the DLL in a class called RFIDReaderClass . To reduce
bandwidth I have only included a partial class definition here. I can
call all the methods of the DLL without any errors.
My test application is a form with a list view. Whenever a callback is
made the list view is updated with some information using an
"Invoke" call to a method that adds an item to the list view. When
I run the application, in the debugger, I can see a few messages
displayed in the list view then suddenly the program goes away. No
error messages are displayed and I am able to "start debugging"
again.
I suspect that this may be a garbage collection issue but I am stumped.
I have tried KeepAlive and GCHandle.Alloc without success, but I am
probably making the calls incorrectly.
By the way, if I don't register the callback using
RFIDRegisterCal lback method of the DLL then the program doesn't
disappear and seems to run correctly. Unfortunately I need to register
the callback in order to do any useful processing in my application.
Here is the RFIDReaderClass .vb
----------------------------------------------------------------------------------------
Imports System.Runtime. InteropServices
<StructLayout(L ayoutKind.Seque ntial, CharSet:=CharSe t.Ansi)> _
Public Structure RFIDInitStructu re
Public MaximumNumberOf Readers As Integer
Public TagSerialNumber Length As Integer
Public TagMemorySize As Integer
Public BoardInfoFile As String
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure ReaderLocationS tructure
Public ReaderNumber As Integer
Public ChipIndex As Integer
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure ReaderLocationA rray
<MarshalAs(Unma nagedType.ByVal Array, SizeConst:=500) > _
Public vals As ReaderLocationS tructure()
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure TagSerialNumber Structure
<MarshalAs(Unma nagedType.ByVal Array, SizeConst:=9)> _
Public Bytes As System.Byte()
End Structure
<StructLayout(L ayoutKind.Seque ntial)> _
Public Structure TagDataStructur e
<MarshalAs(Unma nagedType.ByVal Array, SizeConst:=1025 )> _
Public Bytes As System.Byte()
End Structure
Public Delegate Sub CallbackDelegat e( _
ByVal ReaderLocation As ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Public Class RFIDReaderClass
Public Declare Function RFIDRegisterCal lback Lib "rfidreader.dll " _
(ByVal AddressOfSub As CallbackDelegat e) As Integer
Public Declare Function RFIDDllInitiali ze Lib "rfidreader.dll " _
(ByRef InitData As RFIDInitStructu re) As Integer
Public Declare Function RFIDDiscoverRea ders Lib "rfidreader.dll " _
(ByRef ReaderLocations As ReaderLocationA rray, _
ByRef NumberOfReaders Found As Integer) As Integer
End Class
----------------------------------------------------------------------------------------
Here is the Form1.vb
----------------------------------------------------------------------------------------
Imports System.Runtime. InteropServices
Public Class Form1
Dim RFIDReader As RFIDReaderClass
Dim RFIDCallbackFun ction As New CallbackDelegat e(AddressOf
RFIDReaderCallb ack)
Dim NumberOfReaders Found As Integer
Dim ReaderLocations As ReaderLocationA rray
Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load
Dim InitData As RFIDInitStructu re
InitData.Maximu mNumberOfReader s = 111
InitData.TagMem orySize = 1024
InitData.TagSer ialNumberLength = 8
InitData.BoardI nfoFile = "c:/NTcommgr.csv"
Dim Result As Integer
Result = RFIDReader.RFID RegisterCallbac k(RFIDCallbackF unction)
Result = RFIDReader.RFID DllInitialize(I nitData)
Result = RFIDReader.RFID DiscoverReaders (ReaderLocation s,
NumberOfReaders Found)
End Sub
Private Sub RFIDReaderCallb ack(ByVal ReaderLocation As
ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Dim d As New updateLabel(Add ressOf updateLabelHand ler)
Me.Invoke(d, New Object() {ReaderLocation , ReaderStatus,
TagSerialNumber , TagData})
End Sub
Private Delegate Sub updateLabel(ByV al ReaderLocation As
ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Private Sub updateLabelHand ler(ByVal ReaderLocation As
ReaderLocationS tructure, _
ByVal ReaderStatus As Integer, _
ByVal TagSerialNumber As TagSerialNumber Structure, _
ByVal TagData As TagDataStructur e)
Dim DisplayString As String
DisplayString = Now.ToShortTime String() & " Slot " & _
ReaderLocation. ReaderNumber.To String() & _
" Index " & ReaderLocation. ChipIndex.ToStr ing() & _
" Status " & ReaderStatus.To String()
DisplayListBox. Items.Add(Displ ayString)
End Sub
Protected Overrides Sub Finalize()
MyBase.Finalize ()
End Sub
End Class