DynamicDataDisplay中CursorCoordinateGraph显示时间

CursorCoordinateGraph cursorGraph = new CursorCoordinateGraph();

// setting new text mappings
cursorGraph.XTextMapping = value =>
{
　　if (Double.IsNaN(value))
　　　　return "";

　　DateTime time = dateAxis.ConvertFromDouble(value);
　　return time.ToString("yyyy/MM/dd HH:mm:ss");
};
    cursorGraph.LineStroke = new SolidColorBrush(Colors.Red);
plotter.Children.Add(cursorGraph);