Question

I have a Server class which it basically waits for connections from a client. Inside that class I create an NetworkStream object in order to be able to receive bytes from a client. Because the NetworkStream.Read() method is not asynchronous (meaning that it will wait until it reads bytes from a client in order to proceed executing code similar to the messagebox method), I have to read for bytes in a separate thread so that the user using the program can still interact with the program if the program happens to be waiting to read for data.

anyways a lot of objects are owned by that thread. One example is that I have a List called log in that class. I use that list to know the status of the server. Maybe it is listening for a connection or perhaps it’s status is “connected” or “disconnected”.

So if I do something like:

Server myServer = new Server("192.168.0.120","1300"...\\ I pass the appropite parameters in order to instantiate it

//...
.. then I am able to latter look at the log as
string foo = myServer.Log[0] for example.

because I want to know when the log is updated, on the server class I have created an event as:

    public delegate void onUpdateHandler(string newStatus);
    public event onUpdateHandler onUpdate = delegate { };

I then fire events on the Server class as:

 onUpdate("waitingForConnection");

and I receive those events with the method:

but if I try to do something with newStatus I get the error stating:

System.InvalidOperationException: The calling thread cannot access this object because a different thread owns it.

so how can I pass an object with an event?

---

Edit

so I also notice that if I do:

I also get an error!

but when I do the same thing calling that from a button as:

   // SERVER IS RUNNING BEFORE CALLING THIS METHOD
    private void button3_Click(object sender, RoutedEventArgs e)
    {

        listView1.Items.Add("my own string");

    }

I do NOT get an error!

why is it that I get an error with the event and I do not get an error when calling it with a regular button.

Answer 1

The problem is that the thread tries to access the ListView which is a DependencyObject which has thread affinity, use the Dispatcher to execute methods like this on the UI-thread, e.g.:

Application.Current.Dispatcher.Invoke((Action)(() =>
{
    listView1.Items.Add(newStatus);
}));

Also see the threading model reference for additional info.