Changing background color of a listbox's cell - xojo

Question

Working on a desktop application and having a probably silly problem that's still managing to driving me mad.
I have a listbox that gets its rows from a dynamic source.
I'm trying to change the forecolor of specific cells in the control if the underlying data for that cell changes to specific conditions.
The control also gets drawn once before the condition starts being checked,meaning every cells starts painted with the same (white) forecolor.
Also, this listbox sits inside a Canvas, and that Canvas is in turn inside a Window control.
This code checks for the condition vs. all the rows in the listbox:
for each dict as Dictionary in WidgetsDictionary
Dim site as String = dict.Value("Site").StringValue
Dim device as String = dict.Value("Device").StringValue
Dim sensor as String = dict.Value("Sensor").StringValue
for intC as integer = 0 to actualLstBox.ListCount
Dim siteComp as String = actualLstBox.Cell(intC,4)
Dim deviceComp as String = actualLstBox.Cell(intC,0)
Dim sensorComp as String = actualLstBox.Cell(intC,1)
if actualLstBox.Cell(intC,4) = site AND
actualLstBox.Cell(intC,1) = sensor AND
actualLstBox.Cell(intC,0) = device then
actualLstBox.CellTag(intC,2) = RGB(255, 192, 203)
exit For
end
next
next
Where WidgetsDictionary contains the conditions I need to check against.
And that works,if i check the CellTags after it runs I find them set correctly where they are supposed to be.
Now,if after that code i call
actualLstBox.Refresh()
Note: I know Refresh isn't optimal but I need it to fire as soon as possible
I see the code jumping to the CellBackgroundPaint event of the ListBox
There I have this
If (row<me.ListCount ) then
If Me.CellTag(row, column ) <>nil Then
g.ForeColor = me.CellTag(row,column)
g.FillRect(0, 0, g.Width, g.Height)
End If
end
And again, I see this code executing correctly.
So, I'd expect the list to be redrawn with the correct cells in the new color.
But nothing changes, I see the CellBackgroundPaint event fire after every refresh but the end result shown is always the default (white) colored cells.
I've tried calling, in order
InvalidateCell on the specific cell
Invalidate on the whole Listbox instead of Refresh (since you never know)
Refresh on the containing Canvas
After the first block of code,to no avail.
So now I'm at a loss on what to try next.
Edit
If i replace the event handler with
If (row mod 2) = 0 Then
g.ForeColor = RGB(232,235,255)
g.FillRect 0, 0, g.Width, g.Height
End If
if column = 2 then
g.ForeColor = RGB(255,253,208)
g.FillRect 0, 0, g.Width, g.Height
end
I get alternating colors for the rows and the whole 3rd column of a different colour.
So I guess the fact that I'm trying to repaint it after the first time it's shown is where the problem lies.

Answer 1

You need to return true from the handler in order to tell Xojo that you already have do e the painting. Otherwise Xojo will do its own FillRect after yours.
Keep in mind that this will also override the selection coloring. Meaning that if the row is selected, your cell won't show that unless you either return false in that case or draw your own special bg color for that case.
Also, what you are talking about is the background color, not foreground color, it seems to me. You could perhaps update your question title accordingly.