c# Why delegate\event doesn't get updated after passing it to another class

Question

I'm having trouble invoking delegates that were added after I pass the event to a specific class, I thought that the delegate get updates as objects..

For example this the class that I'm passing the delegate to:

Updated code (due to some question in the comments)

This is actually +- how I need to run it, Where "ExecutorOnCalculationCompleted" is never invoking (please ignore sleep, and synchronization, I shrink my code to the needed parts)

    class Executor
{

    public delegate void CalculationCompletEventHandler(int score);

    public event CalculationCompletEventHandler CalculationCompleted;

    public void Start()
    {
        CalculationCompleted += OnCalculationCompleted;
        Plus plus = new Plus(1, 2, CalculationCompleted);
        Minus minus =  new Minus(5, 2, CalculationCompleted);
        Multi multi =  new Multi(5, 2, CalculationCompleted);
        ...
        ...    They will work async...
    }

    private void OnCalculationCompleted(int score)
    {
        Console.WriteLine("OnCalculationCompleted , score=" + score);
    }
}

class Plus
{
    private Executor.CalculationCompletEventHandler _calculationCompletEventHandler;
    private int a;
    private int b;

    public Plus(int a, int b,Executor.CalculationCompletEventHandler calculationCompletEventHandler)
    {
        this.a = a;
        this.b = b;
        _calculationCompletEventHandler = calculationCompletEventHandler;
    }

    public void Calculate()
    {
        _calculationCompletEventHandler?.Invoke(a+b);
    }
}



class Program
{

    static void Main(string[] args)
    {
        Executor executor = new Executor();
        executor.Start(); // async action
        executor.CalculationCompleted += ExecutorOnCalculationCompleted;
        ...
    }

    // This method doesn't get invoked when the class inside Executor fire the event.
    private static void ExecutorOnCalculationCompleted(int score)
    {
        Console.WriteLine("ExecutorOnCalculationCompleted , score=" + score);
    }
}

that's because the reference of delegates are not same. `+=` creates a new delegate using Delegate.Combine — M.kazem Akhgary, Jan 16 '17 at 14:09
actually the event must be inside `Plus` method, you write same event for `Subtract` etc, the delegate must be in global namespace, don't put it inside a class. `Executor` subscribes its methods to the individual events of Plus and Subtract etc — M.kazem Akhgary, Jan 16 '17 at 14:14
What are you actually trying to do here? What is your goal? For this to work, `Plus` needs to own the event, but then what happens with you add a `Multiply` class? — 15ee8f99-57ff-4f92-890c-b56153, Jan 16 '17 at 14:16
Hi @M.kazemAkhgary , I updated my code hope this will clarify some questions — Aviram Fireberger, Jan 16 '17 at 14:32
Please reduce this to a [mcve]. There currently isn't enough to actually run the code, but you *do* have more than you need. — Jon Skeet, Jan 16 '17 at 14:53
No, that's not a [mcve]. Can I copy/paste/compile/run? No... (`...` isn't valid code.) — Jon Skeet, Jan 17 '17 at 07:31

Nico · Accepted Answer · 2017-01-16T14:41:42.463

You are passing the delegate directly in the constructor. I think you want to put the event into the class. Example:

class Plus
{
    public delegate void CalculationCompletEventHandler(int score);
    public event CalculationCompletEventHandler CalculationCompleted;

    private int a;
    private int b;

    public Plus(int a, int b)
    {
        this.a = a;
        this.b = b;
    }

    public void Calculate()
    {
        if (CalculationCompleted != null)
        {
            CalculationCompleted(a + b);
        }
    }
}

you can now use it like that:

void Main()
{
    Plus plus = new Plus(1, 2);
    plus.CalculationCompleted += OnCalculationCompleted;
    plus.Calculate();

    plus.CalculationCompleted += OnCalculationCompleted2;
    plus.Calculate();        
}

private void OnCalculationCompleted(int score)
{
    Console.WriteLine("OnCalculationCompleted , score=" + score);
}

private void OnCalculationCompleted2(int score)
{
    Console.WriteLine("OnCalculationCompleted2 , score=" + score);
}

As mentioned in the comment, you maybe only need the event itself if the delegate type is used in different parts of your program.

After Update in Question

If you want the event in the executor, I would simply pass an action to each of your classes like Plus, Multiply, ... and invoke the event from the executor:

class Executor
{
    public delegate void CalculationCompletEventHandler(int score);
    public event CalculationCompletEventHandler CalculationCompleted;

    public void Start()
    {
        CalculationCompleted += OnCalculationCompleted;
        Plus plus = new Plus(1, 2, FireEvent);        
    }

    private void FireEvent(int score)
    {
        if (CalculationCompleted != null)
        {
            CalculationCompleted(score);
        }
    }

    private void OnCalculationCompleted(int score)
    {
        Console.WriteLine("OnCalculationCompleted , score=" + score);
    }
}

class Plus
{
    private int a;
    private int b;
    private Action<int> completionAction

    public Plus(int a, int b, Action<int> completionAction)
    {
        this.a = a;
        this.b = b;
        this.completionAction = completionAction;       
    }

    public void Calculate()
    {
        this.completionAction(a + b);
    }
}

that's right but since this delegate (`CalculationCompletEventHandler`) seems to be shared across multiple classes (as its name suggets) it shouldn't be inside `Plus`, so it can be used for say `Subtract` etc — M.kazem Akhgary, Jan 16 '17 at 14:18
@M.kazemAkhgary ok, then only the event should be inside the `Plus` class — Nico, Jan 16 '17 at 14:19
Hi @Nico , I updated my code hope this will clarify some questions — Aviram Fireberger, Jan 16 '17 at 14:33
Yep!, that will do the trick! invoking the event from the parent class. Thanks! — Aviram Fireberger, Jan 16 '17 at 14:58

c# Why delegate\event doesn't get updated after passing it to another class

Updated code (due to some question in the comments)

1 Answers1

After Update in Question