Why can I only read properties and not set properties from ASP.NET web app when using .NET remoting?

Question

Hi everyone. I'm having an issue with attempting to set a property on a remote object hosted in a Windows Service. I'm trying to change a property of an object and it is not saving for some reason.

Here is the pertinent code of the service:

    private static List<Alert> _alerts = new List<Alert>(); // List of the Alerts
    private TcpChannel _tcpChannel;

    protected override void OnStart(string[] args)
    {
        loadAlerts(); // This sets up the List (code not req'd)
        // Set up the remotelister so that other processes can access _alerts
        // Create the TcpChannel
        _tcpChannel = new TcpChannel(65000);
        ChannelServices.RegisterChannel(_tcpChannel, false);

        // Register the Proxy class for remoting.
        RemotingConfiguration.RegisterWellKnownServiceType(
          typeof(RemoteLister),
          "AlertList.soap",
          WellKnownObjectMode.Singleton);
    }

    [Serializable]
    public class RemoteLister : MarshalByRefObject
    {
        public List<Alert> TheList
        {
            get { return _alerts; }
            set { _alerts = value; }
        }

        public bool save()
        {
            EventLog.WriteEntry("AlertService", "Calling saveAlerts...");
            return saveAlerts();
        }
    }

Here is the code for the Alert class (a lot of other stuff too):

    private string _alertName; // Name of alert

    public string AlertName
    {
        get { return _alertName; }
        set { _alertName = value; }
    }

Now in my ASP.NET web app, here's how I initialize everything:

AlertService.RemoteLister remoteAlertList;

    protected void Page_Load(object sender, EventArgs e)
    {
        // This is where we create a local object that accesses the remote object in the service
        Type requiredType = typeof(AlertService.RemoteLister);
        // remoteAlertList is our reference to the List<Alert> in the always running service
        remoteAlertList = (AlertService.RemoteLister)Activator.GetObject(requiredType,
                "tcp://localhost:65000/AlertList.soap");
    }

So now the following code works:

private void fillFields()
    {
        AlertNameTextBox.Text = remoteAlertList.TheList[AlertDropDownList.SelectedIndex].AlertName;
    }

But when I go to change that property as in the following, it doesn't work.

 protected void AlertSaveButton_Click(object sender, EventArgs e)
    {
        remoteAlertList.TheList[AlertDropDownList.SelectedIndex].AlertName = AlertNameTextBox.Text;
    }

Does anyone have an idea of why it wouldn't save that property?

Thanks in advance!

Answer 1

I would guess that since List<T> doesn't inherit from MarshalByRefObject, when you call the property remoteAlertList.TheList you get a disconnected object. Perhaps add an indexer to the object instead:

public class RemoteLister : MarshalByRefObject
{
    public Alert this[int index] {get {...} set {...}}
}

Actually, I would mainly say ditch remoting and use WCF/SOA. And there is little purpose in RemoteLister being [Serializable]. You might also want to put some thought into thread-safety.

---

To clarify; the Alert instances will also be standalone, so local updates won't affect the server; basically, you have two scenarios:

• if the type is MarshalByRefObject, then it only lives at the server; all client operations are remoted to the actual object - but only for MarshalByRefObjecf types
• otherwise, the object is serialized and an actual object is reconstructed.

If you an indexer with (for example)

obj[index].Name = "abc";

then this is:

var tmp = obj[index]; // tmp points to the deserialized disconnected Alert
tmp.Name = "abc"; // we update the local disconnected Alert

(if Alert was MarshalByRefObject, this would update the server, but don't do that). But if we push the value back:

obj[index] = tmp;

then we have updated the server.

As you've discovered, an operation-centric design may be far simpler (i.e. setAlertName). But I really think remoting is a bad idea here.

Answer 2

Tried the indexer, no luck with that. I tried another way shown below and it worked, but it seems like a workaround and not the proper way of doing it. All I did was add this in the RemoteLister class:

public void setAlertName(int index, string name)
            {
                _alerts[index].AlertName = name;
            }

And then changed the save button as follows:

protected void AlertSaveButton_Click(object sender, EventArgs e)     
{     
    remoteAlertList.setAlertName(AlertDropDownList.SelectedIndex, AlertNameTextBox.Text);    
}

I suppose this will get me by for now, but i'd rather do it the "right" way if anyone knows why it wasn't working the first way I did it.