vb.net 2003: trying to speed up an owner-drawn listbox

I'll post only relevent code...

My intent here is a logging system that uses an owner drawn listbox (fixed item height) for custom item background colors (to denote the 'alert level' of the specific item). I'm using a custom class called 'ColorListItem' to store the Text and the Background color of the item:

VB Code:

Public Class ColorListItem
    Public Text As String
    Public Color As System.Drawing.Color
 
    Public Sub New(ByVal NewText As String, ByVal NewColor As System.Drawing.Color)
        Text = NewText
        Color = NewColor
    End Sub
End Class

Each item in the listbox is added in the format of:

VB Code:

lbConsole.Items.Add(New ColorListItem("Text", Drawing.Color.Red)

(Simply an example)

The listbox, lbConsole, has DrawMode set to OwnerDrawFixed so that the MeasureItem event isn't fired. I put the DrawItem event in the sub Log_DrawItem

VB Code:

Sub Log_DrawItem(ByVal sender As Object, ByVal e As System.Windows.Forms.DrawItemEventArgs)
        Dim bg As SolidBrush
        Dim cli As Object 'ColorListItem
        'We use Object just incase the item was improperly added
 
        If e.Index = -1 Then Exit Sub 'it looks good when there are no items, no drawing needed
 
        cli = sender.Items(e.Index)
 
        Try 'if cli isn't a valid ColorListItem
            bg = New SolidBrush(cli.color)
        Catch
            bg = New SolidBrush(Drawing.Color.Yellow) 'highlight any problems
        End Try
 
        e.Graphics.FillRectangle(bg, e.Bounds)
        e.Graphics.DrawString(cli.text, e.Font, New SolidBrush(Drawing.Color.Black), e.Bounds.X, e.Bounds.Y)
    End Sub

If, for some reason, it's unable to use the Color property of 'cli', it defaults to yellow. (The scheme I'm using is red-based so it will stand out.)

I intend that the listbox forces it's color scheme over the standard windows colors cheme (i.e. color.black vs systemcolors.controltext)

I also intend that no selection is visible. Alas, I can not set the selection mode to none, becuase I have to be able to scroll to the most recently added item at the bottom (this is done elsewhere in the code).

The issue I'm noticing is that when the listbox adds an item forcing the listbox to scroll, it flickers horribly. I'd like to have it draw as if the drawmode was Normal.

I'm thinking the drawing each item from it's own thread might speed it up, but I can't figure out how to impliment that.

Any ideas to reduce the flicker?

<shot in the dark>
maybe using BeginUpdate and EndUpdate will help to reduce the flickering?
</shot in the dark>

Quote:

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Originally Posted by The Dutch Dude

<shot in the dark>
maybe using BeginUpdate and EndUpdate will help to reduce the flickering?
</shot in the dark>

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Actually, that increased the flickering to a horrible level whereas it's just bad now.

The way I had coded it was also pretty bad. To make it compatible with the way I intend to do things now, I have to re-write the code for that and in doing so, I'm going to double-buffer the whole thing to see if that works.

Weird... BeginUpdate should stop the listbox from doing anything and display utterly nothing, a grey mass at the most, but it should not flicker. But I'll be interested to hear how this is solved..

its mainly because the EndUpdate causes the whole thing to be re-drawn which causes all of the items to be redrawn. It doesn't call the drawitem event, but it does BeginUpdate...EndUpdate each time a new item is added or otherwise drawn.

Ah, right, BeginUpdate should be placed before and EndUpdate should be placed after any adding takes place, then it should only redraw once, which is the point of the 2 methods, to stop the redrawing when an item is added.
So:

VB Code:

myBootaliciousListBox.BeginUpdate()
 
' example loop
while somethingOrOther
  myBootaliciousListBox.Items.Add(New ColorListItem("Text", Drawing.Color.Red)
end while
 
myBootaliciousListBox.EndUpdate()

I'll give that a try...

Quote:

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Originally Posted by The Dutch Dude

Ah, right, BeginUpdate should be placed before and EndUpdate should be placed after any adding takes place, then it should only redraw once, which is the point of the 2 methods, to stop the redrawing when an item is added.
So:

VB Code:

myBootaliciousListBox.BeginUpdate()
 
' example loop
while somethingOrOther
  myBootaliciousListBox.Items.Add(New ColorListItem("Text", Drawing.Color.Red)
end while
 
myBootaliciousListBox.EndUpdate()

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