Question

I have the following classes:

        using System;
        using System.Windows.Forms;

        namespace FastEyeControl
        {
            public partial class ConnectView : Form, IConnectView
            {
                private IConnectPresenter m_Presenter;

                public ConnectView()
                {
                    InitializeComponent();

                    m_Presenter = new ConnectPresenter(this);
                }

                public string Hostname
                {
                    get
                    {
                        return m_Hostname.Text;
                    }
                }

                public int Port
                {
                    get
                    {
                        return Convert.ToInt32(m_Port.Text);
                    }
                }

                public void ShowMessage(string message)
                {
                    MessageBox.Show(message,
                                    "Success",
                                    MessageBoxButtons.OK,
                                    MessageBoxIcon.Information);
                }

                public void ShowError(string message)
                {
                    MessageBox.Show(message,
                                    "ERROR!",
                                    MessageBoxButtons.OK,
                                    MessageBoxIcon.Error);
                }

                private void m_ConnectButton_Click(object sender, EventArgs e)
                {
                    m_Presenter.ConnectButtonPressed();
                }
            }
        }

The presenter class:

        using System;
        using System.Collections.Generic;

        namespace FastEyeControl
        {
            public class ConnectPresenter : IConnectPresenter
            {
                private IConnectView m_View;
                private IConnectModel m_Model;

                public ConnectPresenter(IConnectView view)
                {
                    m_View = view;
                    m_Model = FastEyeClient.Instance;
                }

                public void ConnectButtonPressed()
                {
                    m_Model.Connect(m_View.Hostname, m_View.Port);
                }

                private void ConnectionComplete(object sender, ConnectionEventArgs e)
                {
                    // Code here indicating whether connection was successful and informing the view.
                    // i.e...

                    if (e.IsConnected)
                    {
                        m_View.ShowMessage("Successfully connected.");
                    }
                    else
                    {
                        m_View.ShowError("Unable to connect.");
                    }
                }
            }
        }

The model code runs in another thread. The problem is that when I call m_Model.Connect(), I’m calling code that’s usually running in another thread within the main thread still (the UI thread). This is not a database connection. This is a TCP/IP connection to a server. If I set a variable within the model, then I am doing this from the UI thread which is not thread safe.

I know that with user controls, they have InvokeRequired and Invoke/BeginInvoke operations that will handle this situation. But that is for user controls only. I know you can’t just interrupt another thread in the middle of its execution and tell it to call another method instead. I basically want the non-UI thread to call the Connect code somehow.

Just as a test, I tried using a delegate (fire off an event whenever I want to connect) and when I look in the debugger, the Connect code is still running in the UI thread.

I need a multi-threaded event queue essentially. What’s the best way to achieve what I want to do here? Thanks!

Answer 1

 public void ConnectButtonPressed()
            {
                var threadedTask = () => m_Model.Connect(m_View.Hostname, m_View.Port);
                threadedTask.BeginInvoke(null,null);
            }

This will, no question, use a background thread from the ThreadPool to do the work. Maybe you had tried to call the delegate directly, or called Invoke() on it; that will execute the delegate synchronously.

Now, BeginInvoke is simple to set up, but it has its limitations; you cannot cancel execution of the background thread, and if it throws an exception you cannot catch it in the invoking thread.