I have a chart widget which have 3 signals. When there is an interrupt for example to show high pressure, I want to place a mark like a vertical line on the buttom of the chart. The graph is circular and so I dont want to make another widget on top of my chart, since I want the line to be dissapeared when the last place where the line was redrawn. There might happen to appear periodic interrupt every other second.
In the case of making widget, i should remove it when the last place is gowing to be redrawn. I dont think making and omitting dynamically would be a good idea for this case.