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.ToLongTimeString();
};

plotter.Children.Add(cursorGraph);

 <c:ChartPlotter.HorizontalAxis>
    <c:HorizontalDateTimeAxis Name="dateAxis"/>
</c:ChartPlotter.HorizontalAxis>

private EnumerableDataSource<StockInfo> CreateCurrencyDataSource(List<StockInfo> rates)
{　　EnumerableDataSource<StockInfo> ds = new EnumerableDataSource<StockInfo>(rates);

　　ds.SetXMapping(ci => dateAxis.ConvertToDouble(ci.Date));
　　ds.SetYMapping(ci => ci.Rate);
　　return ds;

}