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VB 6 Helper Newsletter
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Rod Stephens
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Oct 09, 2009 09:47 PDT
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These days I often have examples that work in .NET but not in VB 6, bit
it's not too often that I post an example that works in VB 6 but not in
.NET.
This week I've posted an example that gets an object's reference count
(the number of variables pointing to it). Because VBN .NET uses garbage
collection instead of reference counting (a mistake IMHO), you can't do
this in VB .NET.
Have a great week and thanks for subscribing!
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Rod
RodSte-@vb-helper.com
Books To Keep: http://www.BooksToKeep.com
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*** Now Available ***
Beginning Database Design Solutions
http://www.amazon.com/exec/obidos/ASIN/0470385499/vbhelper/
Visual Basic 2008 Programmer's Reference
http://www.amazon.com/exec/obidos/ASIN/0470182628/vbhelper/
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VB6 Contents:
1. New HowTo: Get an object's reference count in Visual Basic 6
2. New HowTo: Send a window to the top or bottom in Visual Basic 6
Both Contents:
3. New Links
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1. New HowTo: Get an object's reference count in Visual Basic 6
http://www.vb-helper.com/howto_get_reference_count.html
http://www.vb-helper.com/HowTo/howto_get_reference_count.zip
The GetRefCount function looks at the memory address 4 bytes after an
object reference's address and copies the long integer value there. It
subtracts 3 to adjust for extra references added by the call to the
function.
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory"
(dest As Any, src As Any, ByVal nbytes As Long)
' Return the number of references to the object.
' We subtract 3 to adjust for references made by parameters.
Private Function GetRefCount(ByRef obj As IUnknown) As Long
If obj Is Nothing Then Exit Function
CopyMemory GetRefCount, ByVal (ObjPtr(obj)) + 4, 4
GetRefCount = GetRefCount - 3
End Function
The program makes a collection containing a reference to a form. The Add
Reference button adds a new reference to that same object. The Remove
Reference button removes a reference.
As the program adds and removes references, it displays the number of
references to that object and the number of items in the collection
(they should match).
Private References As Collection
' Make a Form1 instance to have references to.
Private Sub Form_Load()
Set References = New Collection
References.Add New Form1
lblResults.Caption = GetRefCount(References(1)) & " references"
lblNumItems.Caption = References.count & " items"
End Sub
' Add a new reference.
Private Sub cmdAddReference_Click()
References.Add References(1)
lblResults.Caption = GetRefCount(References(1)) & " references"
lblNumItems.Caption = References.count & " items"
cmdRemoveReference.Enabled = True
End Sub
' Delete a reference.
Private Sub cmdRemoveReference_Click()
References.Remove References.count
lblResults.Caption = GetRefCount(References(1)) & " references"
lblNumItems.Caption = References.count & " items"
cmdRemoveReference.Enabled = (References.count > 1)
End Sub
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2. New HowTo: Send a window to the top or bottom in Visual Basic 6
http://www.vb-helper.com/howto_send_to_top_bottom.html
http://www.vb-helper.com/HowTo/howto_send_to_top_bottom.zip
The program uses the SetWindowPos API function to move the window to the
top or bottom.
Private Declare Function SetWindowPos Lib "user32" (ByVal hwnd As Long,
ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal
cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long
Private Const SWP_NOMOVE = &H2
Private Const SWP_NOSIZE = &H1
Private Const HWND_BOTTOM = 1
Private Const HWND_TOP = 0
Private Sub cmdSendToBack_Click()
Dim flags As Long
flags = SWP_NOSIZE Or SWP_NOMOVE
SetWindowPos Me.hwnd, HWND_BOTTOM, 0, 0, 0, 0, flags
End Sub
Private Sub cmdBringToFront_Click()
Dim flags As Long
flags = SWP_NOSIZE Or SWP_NOMOVE
SetWindowPos Me.hwnd, HWND_TOP, 0, 0, 0, 0, flags
End Sub
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3. New Links
http://www.vb-helper.com/links.html
Enable Technology Training
http://www.enableit.co.uk
Training in VBA, ASP, ASP.NET, SQL Server, etc. in West Midlands and
Birmingham.
Advanced Outlook Repair
http://www.repair-outlook.com/
Outlook recovery tool that scans damages folders to recover messages,
folders, etc.
calnet Technology Group
http://calnettech.com/
Computer support and IT Services in the Los Angeles/Irvine/Long Beach
area.
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