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| Title | Change controls faster by preventing window updates |
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| Description | This example shows how to change controls faster by preventing window updates in Visual Basic 6. It uses the LockWindowUpdate API function to prevent Windows from updating while it makes the changes. |
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| Keywords | LockWindowUpdate, modify control, change control |
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| Categories | Controls, Windows, Tips and Tricks |
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Thanks to David Jacquet.
If you check the Lock Updates box, the program calls the LockWindowUpdates API function. It then loads a bunch of values into a ListBox, unlocks updates if it previously locked them, and displays the elapsed time.
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Private Sub Command1_Click()
Dim start_time As Single
Dim i As Long
Dim num_items As Long
num_items = CLng(txtNumItems.Text)
List1.Clear
lblTime.Caption = ""
MousePointer = vbHourglass
DoEvents
start_time = Timer
If Check1.Value = vbChecked Then
' Lock the window to prevent updates.
LockWindowUpdate List1.hWnd 'locks the refresh
' control
End If
' Create the list items.
For i = 1 To num_items
List1.AddItem "Item " & Format$(i) & _
" of " & Format$(num_items)
Next i
If Check1.Value = vbChecked Then
' Unlock the window so it can update again.
LockWindowUpdate 0
End If
lblTime.Caption = Format$(Timer - start_time, "0.00") & _
_
" seconds"
MousePointer = vbDefault
End Sub
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In one test, the program took 4.99 seconds to load 30,000 list items without locking. It took only 3.4 seconds with LockWindowUpdate.
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