关于c＃：对象引用未设置为对象的实例。

Object reference not set to an instance of an object. in wcf service

我创建了一个WCF服务和客户端应用程序来与该服务通信。当服务将数据发送到客户端应用程序时，我的项目工作正常，但在将数据发送回服务时出错，并且在服务端出现这样的错误

An exception of type 'System.NullReferenceException' occurred in HostWCF.DLL but was not handled in user code Additional information: Object reference not set to an instance of an object.

这是客户端调用和获取服务器或服务器数据的函数：

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us = client.GetDataFromServerForTenderMaster(machine);
cmd.Connection = con;
SubmitDataCollection sDC = new SubmitDataCollection();
string sqlcommand ="";
try
{
foreach (HostWCF.TableNameTenderMaster item in sDC.SubmitToTableNameTenderMaster())
{
Console.WriteLine(client.State);
Console.ReadLine();
do
{

sub = client.SubmitDataToServerForTenderMaster(machine, item);
if (sub == true)
{
if (item.DeleteStatus == true)
{
DeleteStatus = 1;
}
else
{
DeleteStatus = 0;
}
if (item.Local == true)
{
LocalStatus = 1;
}
else
{
LocalStatus = 0;
}
if (item.Global == true)
{
GlobalStatus = 1;
}
else
{
GlobalStatus = 0;
}
sqlcommand ="UPDATE [TenderMaster] SET [TenderCode] =" + item.TenderCode
+" ,[TenderCodeNumber] = '" + item.TenderCodeNumber +"' ,[TenderName] =
'" + item.TenderName +"' ,[StartingDate] = '" + item.StartingDate +"'
,[EndingDate] = '" + item.EndingDate +"' ,[ClientName] = '" +
item.ClientName +"' ,[Address] = '" + item.Address +"' ,[ContractoreName]
= '" + item.ContractoreName +"' ,[WorkName] = '" + item.WorkName +"'
,[WorkOrderNo] = '" + item.WorkOrderNo +"' ,[STno] = '" + item.STno +"'
,[VatNo] = '" + item.VatNo +"' ,[Estimatetime] = '" + item.Estimatetime
+"'
,[EstimateAmount] = '" + item.EstimateAmount +"' ,[UserId] = '" +
item.UserId +"' ,[Datetime] = '" + item.Datetime +"' ,[Status] =" +
item.Status +" ,[LocationID] = '" + item.LocationID +"' ,[Sync_Status] ="
+ syncStatus +" ,[Sync_Datetime] = '" + item.Sync_Datetime +"' ,[Layer]
= '" + item.Layer +"',[Dt] = '" + item.Dt +"' ,[Location] = '" +
item.Location +"' ,[Local] =" + LocalStatus +" ,[Global] =" +
GlobalStatus +" ,[DeleteStatus] =" + DeleteStatus +" WHERE [TenderCode] =
" + item.TenderCode +" and [LocationID] = '" + item.LocationID +"' and
[Layer] ='" + item.Layer +"'";

cmd.CommandText = sqlcommand;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
} while (sub == false);

我在服务器端的功能如下：

public bool GetDataFromServerForTenderMaster(string MachineID)

要将数据发送到客户机应用程序，这很好。

public bool SubmitDataToServerForTenderMaster(string MachineID,TableNameTenderMaster tn)

当从客户端应用程序发送数据时，它会在下面的区域中给出错误。

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[DataContract]
public class TableNameTenderMaster
{
private int _TenderCode;
private string _TenderCodeNumber;
private string _TenderName;
private string _StartingDate;
private string _EndingDate;
private string _ClientName;
private string _Address;
private string _ContractoreName;
private string _WorkName;
private string _WorkOrderNo;
private string _STno;
private string _VatNo;
private string _Estimatetime;
private string _EstimateAmount;
private string _UserId;
private DateTime _Datetime;
private int _Status;
private string _LocationID;
private bool _Sync_Status;
private DateTime _Sync_Datetime;
private string _Layer;
private string _Dt;
private string _Location;
private bool _Local;
private bool _Global;
private bool _DeleteStatus;
private bool _UpdateStatus;

[DataMember]
public int TenderCode
{
get
{
return _TenderCode;
}
set
{
if (value == null)
{
value = 0;
}
_TenderCode = value;
}
}
[DataMember]
public string TenderCodeNumber
{
get
{
return _TenderCodeNumber;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_TenderCodeNumber = value.Trim();
}
}
[DataMember]
public string TenderName
{
get
{
return _TenderName;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_TenderName = value.Trim();
}
}
[DataMember]
public string StartingDate
{
get
{
return _StartingDate;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_StartingDate = value.Trim();
}
}
[DataMember]
public string EndingDate
{
get
{
return _EndingDate;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_EndingDate = value.Trim();
}
}
[DataMember]
public string ClientName
{
get
{
return _ClientName;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_ClientName = value.Trim();
}
}
[DataMember]
public string Address
{
get
{
return _Address;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_Address = value.Trim();
}
}
[DataMember]
public string ContractoreName
{
get
{
return _ContractoreName;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_ContractoreName = value.Trim();
}
}
[DataMember]
public string WorkName
{
get
{
return _WorkName;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_WorkName = value.Trim();
}
}
[DataMember]
public string WorkOrderNo
{
get
{
return _WorkOrderNo;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_WorkOrderNo = value.Trim();
}
}
[DataMember]
public string STno
{
get
{
return _STno;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_STno = value.Trim();
}
}
[DataMember]
public string VatNo
{
get
{
return _VatNo;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_VatNo = value.Trim();
}
}
[DataMember]
public string Estimatetime
{
get
{
return _Estimatetime;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_Estimatetime = value.Trim();
}
}
[DataMember]
public string EstimateAmount
{
get
{
return _EstimateAmount;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_EstimateAmount = value.Trim();
}
}
[DataMember]
public string UserId
{
get
{
return _UserId;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_UserId = value.Trim();
}
}
[DataMember]
public DateTime Datetime
{
get
{
return _Datetime;
}
set
{
_Datetime = value;
}
}
[DataMember]
public int Status
{
get
{
return _Status;
}
set
{
if (value == null)
{
value = 0;
}
_Status = value;
}
}
[DataMember]
public string LocationID
{
get
{
return _LocationID;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_LocationID = value.Trim();
}
}
[DataMember]
public bool Sync_Status
{
get
{
return _Sync_Status;
}
set
{
_Sync_Status = value;
}
}
[DataMember]
public DateTime Sync_Datetime
{
get
{
return _Sync_Datetime;
}
set
{
_Sync_Datetime = value;
}
}
[DataMember]
public string Layer
{

get
{
return _Layer;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_Layer = value.Trim();
}
}

private string _SyncMachineID;
[DataMember]
public string SyncMachineID
{
get
{
return _SyncMachineID;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_SyncMachineID = value.Trim();
}
}

[DataMember]
public string Dt
{
get
{
return _Dt;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_Dt = value.Trim();
}
}
[DataMember]
public string Location
{
get
{
return _Location;
}
set
{
if (value.Trim() == null || value.Trim() == string.Empty || value.Trim() =="")
{
value ="";
}
_Location = value.Trim();
}
}
[DataMember]
public bool Local
{
get
{
return _Local;
}
set
{
_Local = value;
}
}
[DataMember]
public bool Global
{
get
{
return _Global;
}
set
{
_Global = value;
}
}
[DataMember]
public bool DeleteStatus
{
get
{
return _DeleteStatus;
}
set
{
_DeleteStatus = value;
}
}
public bool UpdateStatus
{
get
{
return _UpdateStatus;
}
set
{
_UpdateStatus = value;
}
}
}

我做了一些研究，但没有找到解决这个问题的方法。请任何人都知道这个问题的解决办法。