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Tip of the Day
Language: VB5,VB6
Expertise: Advanced
Jun 3, 2000



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Determine whether the client program is in break mode

When an interpreted client running in the IDE enters debug (break) mode, all the ActiveX DLL it's using continue to be in run mode as usual, even though you won't notice it because the DLL will be inactive until the program invokes one of its methods. There are times, however, when the DLL is able to execute independently of the client program, most notably when it contains a form with a Timer on it. Therefore in some cases you may want to stop any processing in the DLL, but unfortunately there is no simple way for a DLL to determine whether its client (interpreted) mode is in break mode or not.

The following code solves the problem. It retreives the handle of the main IDE window, and checks whether its caption contains the string "[break]". Note that when you press the F8 key to single-step on individual statements, the caption of the main IDE window temporarily switches to "[run]", therefore the ClientIsInBreakMode function below will always return False if called from a method exposed by the DLL, and can only return True if called from within a procedure that runs asynchronously with respect to the main program in the IDE.

Private Declare Function EnumThreadWindows Lib "user32" (ByVal dwThreadId As _
    Long, ByVal lpfn As Long, ByVal lParam As Long) As Long
Private Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" _
    (ByVal hWnd As Long, ByVal lpString As String, ByVal cch As Long) As Long
Private Declare Function GetClassName Lib "user32" Alias "GetClassNameA" (ByVal _
    hWnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long

Dim m_ClientIsInBreakMode As Boolean

' Return True if the client application of this DLL is
' a program being interpreted in the VB IDE and
' the IDE is currently in break mode

' NOTE: this code is meant to be inserted in a BAS module
'       inside an ActiveX DLL project

Function ClientIsInBreakMode() As Boolean
    m_ClientIsInBreakMode = False
    EnumThreadWindows App.ThreadID, AddressOf EnumThreadWindows_CBK, 0
    ClientIsInBreakMode = m_ClientIsInBreakMode
End Function

' this is a callback function that is executed for each
' window in the same thead as the DLL

Function EnumThreadWindows_CBK(ByVal hWnd As Long, ByVal lParam As Long) As _
    Dim buffer As String * 512
    Dim length As Long
    Dim windowClass As String
    Dim windowText As String
    ' get the class name of this window
    length = GetClassName(hWnd, buffer, Len(buffer))
    windowClass = Left$(buffer, length)
    If windowClass = "IDEOwner" Then
        ' this is the main VB IDE window
        ' retrieve its caption
        length = GetWindowText(hWnd, buffer, Len(buffer))
        windowText = Left$(buffer, length)
        ' the client is in break mode if the caption of
        ' the main IDE window contains the "[break]" string
        If InStr(windowText, "[break]") Then
            m_ClientIsInBreakMode = True
        End If
        ' in any case, stop enumeration now
        EnumThreadWindows_CBK = False
        EnumThreadWindows_CBK = True
    End If
End Function

Francesco Balena
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