C#

Member 2146223 wrote:

please give me a running program ...

Member 2146223 wrote:

i need to create a program ...

static void Main(string[] args)
{
    new Program();
    Console.ReadLine();
}

public Program()
{
    DoIt();
}

public async void DoIt()
{
    AlarmReceived += () => new Task(() => Console.WriteLine("A"));
    AlarmReceived += () => new Task(() => Console.WriteLine("B"));
    await OnAlarm();
}

AlarmReceived += () => Task.Run(() => Console.WriteLine("A"));
AlarmReceived += () => Task.Run(() => Console.WriteLine("B"));

static void Main(string[] args)
{
    new Program();
    Console.ReadLine();
}

public Program()
{
    DoIt2();
    Console.WriteLine("Waiting for alarms to process...");
}

List<Action> alarmActions = new List<Action>();

public void AddAlarm(Action act)
{
    alarmActions.Add(act);
}

public void RemoveAlarm(Action act)
{
    alarmActions.Remove(act);
}

public async void DoIt2()
{
    Console.WriteLine("Adding alarms");
    AddAlarm(() => Alarm1());
    AddAlarm(() => Alarm2());
    await Task.Run(() => ProcessAlarms());
    Console.WriteLine("Removing alarms");
    RemoveAlarm(() => Alarm1());
    RemoveAlarm(() => Alarm2());
    await Task.Run(() => ProcessAlarms());
}

public void ProcessAlarms()
{
    alarmActions.ForEach(a => a());
}

public void Alarm1()
{
    System.Threading.Thread.Sleep(1000);
    Console.WriteLine("Alarm 1");
}

public void Alarm2()
{
    Console.WriteLine("Alarm 2");
}

Action a = () => Alarm1();
Action b = () => Alarm2();
Console.WriteLine("Adding alarms");
AddAlarm(a);
AddAlarm(b);
await Task.Run(() => ProcessAlarms());
Console.WriteLine("Removing alarms");
RemoveAlarm(a);
RemoveAlarm(b);
await Task.Run(() => ProcessAlarms());

Task a = Task.Run(() =>
{
    System.Threading.Thread.Sleep(1000);
    Console.WriteLine("A");
}));

AlarmReceived += () => a;

        public async void DoIt()
        {
            Task a = Task.Run(() =>
            {
                System.Threading.Thread.Sleep(1000);
                Console.WriteLine("A");
            });

<pre>
        Task b = Task.Run(() => Console.WriteLine("B"));

        AlarmReceived += () => a;
        AlarmReceived += () => b;
        Console.WriteLine("Processing alarms");
        await OnAlarm();

        Console.WriteLine("Unwire");
        AlarmReceived -= () => a;
        AlarmReceived -= () => b;
        await OnAlarm();
    }

    internal async Task OnAlarm()
    {
        if (eAlarmReceived == null)
        {
            Console.WriteLine("eAlarmReceived is null!");
            return;
        }

        // REMARK: ToList() to capture the event list at the moment of the call
        var eTasks = eAlarmReceived.GetInvocationList().Cast<Func<Task>>().ToList();

        if (eTasks.Count == 0)
        {
            Console.WriteLine("Nothing to do!");
        }
        else
        {
            Console.WriteLine("Tasks = " + eTasks.Count);
            foreach (var t in eTasks)
                await t();
        }
    }</pre>

Processing alarms
B
Tasks = 2
Waiting for alarms to process...
A
Unwire
Tasks = 2

Marc Clifton wrote:

But again, the use of the anonymous method for AlarmReceived means you can't unwire it.

    class AlarmSource
    {
        public async Task OnAlarm()
        {
            var eTasks = AlarmReceived?.GetInvocationList()?.Cast<Func<Task>>()?.ToList();
            if (eTasks == null)
                return;
            foreach (var t in eTasks)
                await t();
        }
        public event Func<Task> AlarmReceived;
    }

<pre>
class Consumer
{
    public Consumer(string name = null)
    {
        Name = name;
    }
    public string Name { get; set; }

    public AlarmSource Source
    {
        get { return source; }
        set
        {
            Func<Task> handler = () => Task.Run(() => Console.WriteLine(Name));
            if (source != null)
                source.AlarmReceived -= handler;
            source = value;
            if (source != null)
                source.AlarmReceived += handler;
        }
    }
    AlarmSource source;
}

class Program
{
    static void Main(string[] args)
    {
        DoAsyncStuff().Wait();
        Console.ReadLine();
    }
    static async Task DoAsyncStuff()
    {
        var c1 = new Consumer("A");
        var c2 = new Consumer("B");
        var src = new AlarmSource();
        c1.Source = src;
        c2.Source = src;
        await src.OnAlarm();
        c2.Source = null;
        await src.OnAlarm();
    }
}</pre>

public AlarmSource Source
{
    get { return source; }
    set
    {
        Func<Task> handler = () => Task.Run(() => Console.WriteLine(Name));
        if (source != null)
            source.AlarmReceived -= handler;
        source = value;
        if (source != null)
            source.AlarmReceived += handler;
    }
}
AlarmSource source;

public AlarmSource Source
{
    get { return source; }
    set
    {
        if (source != null)
            source.AlarmReceived -= () => Task.Run(() => Console.WriteLine(Name));
        source = value;
        if (source != null)
            source.AlarmReceived += () => Task.Run(() => Console.WriteLine(Name));
    }
}
AlarmSource source;

How to: Subscribe to and Unsubscribe from Events (C# Programming Guide)[^]

It is important to notice that you cannot easily unsubscribe from an event if you used an anonymous function to subscribe to it. To unsubscribe in this scenario, it is necessary to go back to the code where you subscribe to the event, store the anonymous method in a delegate variable, and then add the delegate to the event. In general, we recommend that you do not use anonymous functions to subscribe to events if you will have to unsubscribe from the event at some later point in your code.

Func<Task> handler = HiddenAnonymousMethod1;
if (source != null)
    source.AlarmReceived -= handler;
source = value;
if (source != null)
    source.AlarmReceived += handler;

if (source != null)
    source.AlarmReceived -= HiddenAnonymousMethod1;
source = value;
if (source != null)
    source.AlarmReceived += HiddenAnonymousMethod2;

private static readonly Task CompletedTask = Task.FromResult(true);

private IEnumerable<Func<Task>> GetAlarmInvocationList()
{
    lock (this)
    {
        Func<Task> handler = eAlarmReceived;
        if (handler == null) return null;
        return handler.GetInvocationList().Cast<Func<Task>>().ToList();
    }
}

internal Task OnAlarm()
{
    var eTasks = GetAlarmInvocationList();
    if (eTasks == null) return CompletedTask;
    
    var tasks = eTasks.Select(fn => fn());
    return Task.WhenAll(tasks);
}

var eTasks = handler?.GetInvocationList()?.Cast<Func<Task>>()?.ToList();
if (eTask == null)
  return;
foreach (var t in eTask)
  await t();