Windows Clipboard Read - Access application hanging

[pwu]

Hi,

I'm trying to read the clipboard. As each new text item is put into
the clipboard by Access form vba code is called by use of the Winproc
callback.

I have one push button which starts the capture:
Private Sub btnCapture_Click()
MsgBox "Capturing...."
HookForm Me
End Sub
I have a push button which ends the capture and prints out everything
that was copied into the clipboard.
Private Sub btnCaptureEnd_Click()
MsgBox "End of Capture."
UnHookForm Me
MsgBox EntireLine
End Sub

However the problem is that once the capture start button is pressed
the application hangs.
That is I cannot hit the capture end button
Can someone please explain how to fix this problem?

The code is shown below.

Thanks for any help
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Option Compare Database

Private Const WM_DRAWCLIPBOARD = &H308
Private Const WM_CHANGECBCHAIN = &H30D
Private Const WM_DESTROY = &H2
Private Const GWL_WNDPROC = -4

Private Const GMEM_MOVABLE = &H2&
Private Const GMEM_DDESHARE = &H2000&
Private Const CF_TEXT = 1

Private Const CLIPBOARDFORMATNOTAVAILABLE = 1
Private Const CANNOTOPENCLIPBOARD = 2
Private Const CANNOTGETCLIPBOARDDATA = 3
Private Const CANNOTGLOBALLOCK = 4
Private Const CANNOTCLOSECLIPBOARD = 5
Private Const CANNOTGLOBALALLOC = 6
Private Const CANNOTEMPTYCLIPBOARD = 7
Private Const CANNOTSETCLIPBOARDDATA = 8
Private Const CANNOTGLOBALFREE = 9

Dim PrevProc As Long
Dim NextClip As Long
Dim EntireLine As String

'---------------------------------------------------------------
' Reads the data in the clipboard
'----------------------------------------------------------------
Public Function GetClipBrdText() As Variant
Dim hMemory As Long
Dim lpMemory As Long
Dim strText As String
Dim lngSize As Long
Dim varRet As Variant

varRet = ""

' Is there text on the clipboard? If not, error out.
If Not CBool(IsClipboardFormatAvailable _
(CF_TEXT)) Then
varRet = CVErr(CLIPBOARDFORMATNOTAVAILABLE)
GoTo GetClipBrdTextDone
End If

' Open the clipboard
If Not CBool(OpenClipboard(0&)) Then
varRet = CVErr(CANNOTOPENCLIPBOARD)
GoTo GetClipBrdTextDone
End If

' Get the handle to the clipboard data
hMemory = GetClipboardData(CF_TEXT)
If Not CBool(hMemory) Then
varRet = CVErr(CANNOTGETCLIPBOARDDATA)
GoTo GetClipBrdTextCloseClipboard
End If

' Find out how big it is and allocate enough space
' in a string
lngSize = GlobalSize(hMemory)
strText = Space$(lngSize)

' Lock the handle so we can use it
lpMemory = GlobalLock(hMemory)
If Not CBool(lpMemory) Then
varRet = CVErr(CANNOTGLOBALLOCK)
GoTo GetClipBrdTextCloseClipboard
End If

' Move the information from the clipboard memory
' into our string
Call MoveMemory(strText, lpMemory, lngSize)

' Truncate it at the first Null character because
' the value reported by lngSize is erroneously large
strText = Left$(strText, InStr(1, strText, Chr$(0)) - 1)
' MsgBox "This item is " & GetClipboardSequenceNumber()
' Free the lock
Call GlobalUnlock(hMemory)

GetClipBrdTextCloseClipboard:
' Close the clipboard
If Not CBool(CloseClipboard()) Then
varRet = CVErr(CANNOTCLOSECLIPBOARD)
End If

GetClipBrdTextDone:
If Not IsError(varRet) Then
GetClipBrdText = strText
Else
GetClipBrdText = varRet
End If
End Function

'-------------------------------------------------------------------------------------------------------------------------------------------------------
' Routine called when a Windows event is called
'--------------------------------------------------------------------------------------------------------------------------------------------------------
Public Function WindowProc(ByVal hwnd As Long, ByVal uMsg As Long,
ByVal wParam As Long, ByVal lParam As Long) As Long
Dim buf As Variant
WindowProc = 0
If uMsg = WM_DRAWCLIPBOARD Then
' Got some text
buf = GetClipBrdText()
EntireLine = EntireLine & " " & buf
End If
WindowProc = CallWindowProc(PrevProc, hwnd, uMsg, wParam, lParam)
End Function

'----------------------------------------------------------------------------------------------------------------------
' Registers routine for windows event and clipboard viewer
'-----------------------------------------------------------------------------------------------------------------------
Public Sub HookForm(F As Form)
Dim Msg As String
PrevProc = SetWindowLong(F.hwnd, GWL_WNDPROC, AddressOf
WindowProc)
If PrevProc = 0 Then
MsgBox "Windows event handler registration failed"
Exit Sub
End If
'Register this form as a Clipboardviewer
NextClip = SetClipboardViewer(F.hwnd)
If NextClip = Null Then
MsgBox "Clipboard registration failed"
End If
End Sub
'---------------------------------------------------------------------------------------------
' Deregisters routine for windows event and clipboard viewer
'----------------------------------------------------------------------------------------------
Public Sub UnHookForm(F As Form)
If NextClip <> Null Then
ChangeClipboardChain F.hwnd, NextClip
End If
If PrevProc <> 0 Then
SetWindowLong F.hwnd, GWL_WNDPROC, PrevProc
End If
End Sub