未将对象引用设置为ASP.Net Webservice中的对象实例

Question

In my Asp.Net web service i use below 2 method to change an existing client's status form a global list oblject named ClientStatus here. This global list is modified from several client side but in a safe way (lock).

private static List<ActiveClient> ClientStatus = new List<ActiveClient>();
public static void SetClinetStatus(string ClientID, int clinetstatus)
{
    ActiveClient activeClient=null;
    try
    {
            activeClient = GetClient(ClientID);
            if (activeClient != null)
            {
                activeClient.statuschanged = true;
                activeClient.status = clinetstatus;
            }
    }
    catch (Exception ex)
    {
        WebserviceLog.Debug(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType + "::" + System.Reflection.MethodBase.GetCurrentMethod().ToString() + ":" + ex.Message);
    }

}

public static ActiveClient GetClient(string clientID)
{
    ActiveClient activeClient = null;
    try
    {
        lock (ClientStatus)
        {
            activeClient = ClientStatus.Find(c => c.clinetID == clientID);
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
    return activeClient;
}

I used below code to pass the value to SetClinetStatus(string ClientID, int clinetstatus) method

string errorData = Encoding.Default.GetString(data);
string[] tokens = errorData.Split(new string[] { ":" }, StringSplitOptions.RemoveEmptyEntries);
if (tokens.Length == 2)
    {                         
     SessionVariables.SetClinetStatus(tokens[0],Convert.ToInt32(tokens[1]));
    }

But sometimes (not every times) i get

Object reference not set to an instance of an object

form

activeClient = GetClient(ClientID);

i don't understand why it is happening and don't see any problem there.

does anyone see any problem there that is responsible for such kind of exception.

EDIT

In the global list i only add client through below method and here clientID will come from direct webservice method. and in another end (from where the client ID comes) i added a check for not to null or empty the clientID.

 public static void AddClient(string clientID)
        {
            try
            {
                lock (ClientStatus)
                {
                    ClientStatus.Add(new ActiveClient { clinetID = clientID });
                }

            }
            catch (Exception ex)
            {
                WebserviceLog.Debug(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType + "::" + System.Reflection.MethodBase.GetCurrentMethod().ToString() + ":" + ex.Message);
            }

        }

and the ActiveClient class structure is

public class ActiveClient
    {
        public ActiveClient()
        {
            clinetID = string.Empty;
            status = 0;
            statuschanged = false;
        }
        public string clinetID { get; set; }
        public int status { get; set; }
        public bool statuschanged { get; set; } 
    }

Answer 1

Try

public static void SetClinetStatus(string ClientID, int clinetstatus)
{
    ClientID = ClientID.Trim();

    // Cannot run unless there is a ClientID submitted
    if(string.IsNullOrEmpty(ClientID))
    {
        // Log handling of event
        return;
    }

    ActiveClient activeClient=null;
    try
    {
        activeClient = GetClient(ClientID);
        if (activeClient != null)
        {
            activeClient.statuschanged = true;
            activeClient.status = clinetstatus;
        }
    }
    catch (Exception ex)
    {
        WebserviceLog.Debug(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType + "::" + System.Reflection.MethodBase.GetCurrentMethod().ToString() + ":" + ex.Message);
    }

}

You should also ensure the clientID is in the ClientStatus

public static ActiveClient GetClient(string clientID)
{
    // Cannot continue without a ClientStatus
    if(ClientStatus == null) 
    {
        return null;
    }

    ActiveClient activeClient = null;
    try
    {
        lock (ClientStatus)
        {
            // Test if there are any matching elements
            if(ClientStatus.Any(c => c.clinetID == clientID))
            {
                activeClient = ClientStatus.Find(c => c.clinetID != null && c.clinetID == clientID);
            }
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }

    // This will return null if there are no matching elements
    return activeClient;
}