Another WM_COPYDATA issue

[Crusader2010]

Hi. Here is some code, i'll write the explanations after:

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)> _
    Public Structure MsgSTR
        Public code As String
        Public index1 As Integer
        Public index2 As Integer
        Public arr() As Integer
    End Structure

<StructLayout(LayoutKind.Sequential)> _
    Public Structure CopyData
        Public dwData As IntPtr
        Public cbData As Integer
        Public lpData As MsgSTR
    End Structure

Private Declare Auto Function SendMessage Lib "user32" _
     (ByVal hWnd As IntPtr, _
      ByVal Msg As Integer, _
      ByVal wParam As IntPtr, _
      ByVal lParam As CopyData) As Boolean

    Private Declare Auto Function FindWindow Lib "user32" _
     (ByVal lpClassName As String, _
      ByVal lpWindowName As String) As IntPtr

    Private Const WM_COPYDATA As Integer = &H4A

Private Function mesajSMSSTR(ByVal msg As MsgSTR) As Boolean
        Dim ClientWindow As IntPtr
        Dim a() As System.Diagnostics.Process = System.Diagnostics.Process.GetProcesses

        For Each p In a
            If UCase(p.ProcessName) = "SOMEPROCESS" Then
                ClientWindow = p.MainWindowHandle
                Exit For
            End If
        Next
       
        If Not ClientWindow.Equals(IntPtr.Zero) Then

            Dim message As MsgSTR = msg
            Dim data As CopyData

            data.lpData = message
            data.cbData = Marshal.SizeOf(message)

            frmTest.SendMessage(ClientWindow, frmTest.WM_COPYDATA, Me.Handle, data)
            Return True
        Else
            Return False
        End If
End Function

Private Sub cmdSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdSend.Click
       
            Dim msg As MsgSTR
            msg.code = Trim(txtCode.Text)
            msg.index1 = CInt(Trim(txtI1.Text))
            msg.index2 = CInt(Trim(txtI2.Text))
            ReDim msg.arr(40)
            For i = 0 To Trim(txtArr.Text).Split(" ").Length - 1
                msg.arr(i) = CInt(Trim(txtArr.Text).Split(" ")(i))
            Next



            If mesajSMSSTR(msg) Then
                MsgBox("Message sent")
            Else
                MsgBox("Message not sent. Process not running.")
            End If
       
End Sub

Basically i have a structure with a string, two 32bit integers and an array of 32bit integers. I need to send this structure using WM_COPYDATA to an application made in VC++ 6.0, from my VB .NET 2008 framework 3.5.

When i execute the code above, only the (first) string is sent. If i comment the lines related to Arr() (both in the structure and in the _click event), only the first 16 characters of my string are being sent.

For testing purposes, the receiving application uses memcopy to get any data that is sent to it and displays it in a messagebox.

I have searched google and these forums a lot for similar problems but everything i tried yielded the same result - the integer values are not sent at all.

If i put 3 strings in my structure instead, only the first is sent. Adding a vbNullString to the end of the first string (MSGSTR.code) results in an empty message box in the receiving application.

Any help is appreciated, thanks.

[Craig Gemmill]

What immediately pops in to my head is that you should change the way that you're declaring the lpData member of CopyData, and then change the way that you pass the data along.

Declare the lpData member as an IntPtr.

Then pin your custom struct to memory so that it's available in it's entirety to your native application.

You can see an example of this here:
http://pinvoke.net/default.aspx/Stru...ATASTRUCT.html

 public static IntPtr IntPtrAlloc<T>(T param)
      {
     IntPtr retval = Marshal.AllocHGlobal(Marshal.SizeOf(param));
     Marshal.StructureToPtr(param, retval, false);
     return (retval);
      }

      public static void IntPtrFree(IntPtr preAllocated)
      {
     if (IntPtr.Zero == preAllocated) throw (new Exception("Go Home"));
    Marshal.FreeHGlobal(preAllocated); preAllocated = IntPtr.Zero;
      }

      [StructLayout(LayoutKind.Sequential)]
      struct COPYDATASTRUCT
      {
     public UInt32 dwData;
     public int cbData;
     public IntPtr lpData;
      }

     IntPtr buffer = IntPtrAlloc(txStruct);
     COPYDATASTRUCT copyData = new COPYDATASTRUCT();
     copyData.dwData = 0xC0b1;
     copyData.lpData = buffer;
     copyData.cbData = Marshal.SizeOf(txStruct);
     IntPtr copyDataBuff= IntPtrAlloc(copyData);
     SendMessage(hWnd, WM_COPYDATA, IntPtr.Zero, copyDataBuff);
     IntPtrFree(copyDataBuff); copyDataBuff = IntPtr.Zero;
     IntPtrFree(buffer); buffer = IntPtr.Zero;

It's not entirely clear, but in the example, your struct would go where the "txStruct" value is used.

Here is some more light reading:
http://msdn.microsoft.com/en-us/library/awbckfbz.aspx

If none of this helps, my next guess would be to double back and make sure that you're treating your structure the same on both ends.

[Crusader2010]

Thanks for the reply. I did try before to allocate memory for my structure and send it as a pointer and got the same result(no integers were sent), but i didn't try to also send the copyData structure as one. I'll get in touch with the other application's designer and see if we can work something out, after which i'll post here about the results.

EDIT: i've made these changes(removed the array for now), but now the message is not sent at all:

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)> _
    Public Structure MsgSTR
        <MarshalAs(UnmanagedType.LPStr, sizeconst:=200)> Public code As String
        <MarshalAs(UnmanagedType.I4)> Public index1 As Integer
        <MarshalAs(UnmanagedType.I4)> Public index2 As Integer
        'Public arr() As Integer
    End Structure

    <StructLayout(LayoutKind.Sequential)> _
    Public Structure CopyData
        Public dwData As IntPtr
        Public cbData As Integer
        Public lpData As IntPtr
    End Structure

    Private Declare Auto Function SendMessage Lib "user32" _
     (ByVal hWnd As IntPtr, _
      ByVal Msg As Integer, _
      ByVal wParam As IntPtr, _
      ByRef lparam As IntPtr) As Boolean

    Private Shared Function pALLOC(Of tip)(ByRef st As tip) As IntPtr
        Dim retval As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(st))
        Marshal.StructureToPtr(st, retval, False)
        Return retval
    End Function

    Private Shared Sub pFREE(ByRef p As IntPtr)
        If p <> IntPtr.Zero Then
            Marshal.FreeHGlobal(p)
            p = IntPtr.Zero
        End If
    End Sub

    Private Function mesajSMS(ByVal msg As MsgSTR) As Boolean
        Dim ClientWindow As IntPtr
        Dim a() As System.Diagnostics.Process = System.Diagnostics.Process.GetProcesses

        For Each p In a
            If UCase(p.ProcessName) = "PROCESSTEST" Then
                ClientWindow = p.MainWindowHandle
                Exit For
            End If
        Next
        ' make sure we found an active client window
        If Not ClientWindow.Equals(IntPtr.Zero) Then
            Dim data As New CopyData
            Dim buffer As IntPtr = pALLOC(Of MsgSTR)(msg)

            data.dwData = ClientWindow
            data.lpData = buffer
            data.cbData = Marshal.SizeOf(msg)

            Dim dataBuff As IntPtr = pALLOC(Of CopyData)(data)

            If frmTest.SendMessage(ClientWindow, frmTest.WM_COPYDATA, Me.Handle, dataBuff) Then
                pFREE(dataBuff) : pFREE(buffer)
                Return True
            Else
                pFREE(dataBuff) : pFREE(buffer)
                Return False
            End If
        Else
            Return False
        End If
    End Function

    Private Sub cmdTrimite_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdTrimite.Click

            Dim msg As New MsgSTR
            msg.code = Trim(txtCode.Text)
            msg.index1 = CInt(Trim(txtIndex1.Text))
            msg.index2 = CInt(Trim(txtIndex2.Text))

            If mesajSMS(msg) Then
                MsgBox("Sent")
            Else
                MsgBox("Not Sent")
            End If
         
       End Sub

The process window is found correctly but the SendMessage function returns false for some reason. Any ideas? thank you.

[Craig Gemmill]

I am able to get this to run. Are you absolutely certain that the target hwnd is correct and that the struct definition is identical on the native side?

At the very least, you should be seeing the WM_COPYDATA message at the target (whether the payload is well-formed or not is another question).