在客户端和主机之间共享对象的WCF

    //Service---------------------------------------------------------
    [DataMember]
    private List<CalculationRecord> History = new List<CalculationRecord>();

    public IEnumerable<CalculationRecord> CalculationHistory()
    {
        return (IEnumerable<CalculationRecord>)History;
    }

    public CalculationResult Calculate(CalculationNode problem)
    {
        CalculationResult calcResult = new CalculationResult();


        //Calculates results of expression
        CalculationEvaluation Evaluator = new CalculationEvaluation();
        Evaluator.Calculate(problem, calcResult);

        return calcResult;
    }
    //interface---------------------------------------------------------
    [ServiceContract]
    public interface ICalculate
    {
        [OperationContract]
        CalculationResult Calculate(CalculationNode problem);

        [OperationContract]
        IEnumerable<CalculationRecord> CalculationHistory();
    }

    //Client------------------------------------------------------------
    CalculatorClient client = new CalculatorClient();
    ICalculate calcProxy = client.ChannelFactory.CreateChannel();

    CalculationNode calcRootNode = parser.Parse(expression);
    CalculationResult result = calcProxy.Calculate(calcRootNode);//result is null