public void crossLines() { TKChartCrossLineAnnotation a = (TKChartCrossLineAnnotation)chart.Annotations [0]; a.Style.VerticalLineStroke = new TKStroke(UIColor.Black); a.Style.HorizontalLineStroke = new TKStroke(UIColor.Black); a.Style.PointShape = new TKPredefinedShape(TKShapeType.Circle, new SizeF(4, 4)); chart.UpdateAnnotations(); }