public CostHistory Compare(Share x, Share y) { if (ReferenceEquals(x, y)) { return(null); } if (ReferenceEquals(x, null)) { return(null); } if (ReferenceEquals(y, null)) { return(null); } if (x.GetType() != y.GetType()) { return(null); } return(new CostHistory((Math.Round(double.Parse(x.CheckTime) - double.Parse(y.CheckTime)), 2).ToString(), x.Cost, (Math.Round(double.Parse(x.Cost) - double.Parse(y.Cost)), 2).ToString())); }