How to implement a cancel event in C#

Question

I know that in C#, there are several built in events that pass a parameter (\"Cancel\") which if set to true will stop further execution in the object that raised the eve

Answer 1

What I needed was a way to stop the subscribers from receiving the event after a subscriber canceled it. In my situation I don't want the event to further propagate to the other subscribers after some subscriber canceled it. I have implemented this using custom event handling:

public class Program
{
    private static List> SubscribersList = new List>();

    public static event EventHandler TheEvent
    {
        add {
            if (!SubscribersList.Contains(value))
            {
                SubscribersList.Add(value);
            }
        }
        remove
        {
            if (SubscribersList.Contains(value))
            {
                SubscribersList.Remove(value);
            }
        }
    }

    public static void RaiseTheEvent(object sender, CancelEventArgs cancelArgs)
    {
        foreach (EventHandler sub in SubscribersList)
        {
            sub(sender, cancelArgs);

            // Stop the Execution after a subscriber cancels the event
            if (cancelArgs.Cancel)
            {
                break;
            }
        }
    }


    static void Main(string[] args)
    {
        new Subscriber1();
        new Subscriber2();

        Console.WriteLine("Program: Raising the event");

        CancelEventArgs cancelArgs = new CancelEventArgs();
        RaiseTheEvent(null, cancelArgs);
        if (cancelArgs.Cancel)
        {
            Console.WriteLine("Program: The Event was Canceled");
        }
        else
        {
            Console.WriteLine("Program: The Event was NOT Canceled");
        }
        Console.ReadLine();
    }
}

public class Subscriber1
{
    public Subscriber1()
    {
        Program.TheEvent += new EventHandler(program_TheEvent);
    }

    void program_TheEvent(object sender, CancelEventArgs e)
    {
        Console.WriteLine("Subscriber1: in program_TheEvent");
        Console.WriteLine("Subscriber1: Canceling the event");
        e.Cancel = true;
    }
}

public class Subscriber2
{
    public Subscriber2()
    {
        Program.TheEvent += new EventHandler(program_TheEvent);
    }

    void program_TheEvent(object sender, CancelEventArgs e)
    {
        Console.WriteLine("Subscriber2: in program_TheEvent");

    }
}