From Xojo Documentation
Redraws the specified cell "from scratch" rather than using the data in the internal buffer.
row and column are zero-based. If you pass a -1 as the row or column parameter, it will redraw the specified entire row or column, i.e., Invalidate(2, -1) redraws row number 2. The CellBackgroundPaint and CellTextPaint events execute when InvalidateCell is called.
InvalidateCell should be necessary only if you are using a custom storage mechanism for your ListBox data. If the contents of the ListBox are stored in the ListBox cells, the ListBox will update automatically as needed.
This method doesn't have a high overhead if used unnecessarily since nothing will happen if the specified cell is not visible.
The following example redraws the specified cell.