Pass parameter to delegate c#

Question

I have an issue that I wish to add function calls to a delegate, but each of these function calls will have a unique parameter. I cannot figure it out or find a solution elsewhere so I am turning to you guys :)

Some pseudo below..

(So basically, I am creating a delegate and an event and the AddToDelegate function is supposed to add the function calls to the event (with a unique value), then the GetData function returns all the responses in one string - the problem comes in the AddToDelegate function as the line a += new A(SomeFunc)(i.ToString()); should really only be a += new A(SomeFunc);)

Is there a way to do this with delegates - or am I barking up the wrong tree?

public delegate string A(string s);
public event A a;

public void AddToDelegate()
{
    for (int i = 0; i < DelegateList.Length; i++)
    {
        a += new A(SomeFunc)(i.ToString());
    }
}

public string GetData()
{
    StringBuilder _sb = new StringBuilder();
    if (a != null)
    {
        Delegate[] DelegateList = a.GetInvocationList();
        for (int i = 0; i < DelegateList.Length; i++)
        {
            _sb.Append(((A)DelegateList[i]));
        }
    }
    return _sb.ToString();
}

The pseudo above would produce a string which details all the unique values — T1gg3rB0unC3, Jul 12 '12 at 13:58
The question asks what you are trying to accomplish, not what the above pseudo-code fails to accomplish. You may indeed be barking up the wrong tree but we can't know it unless you tell us *what* you want to do, rather than *how* you are unable to do it. What are your inputs and what are your expected outputs? Give a usage example, rather than an implementation example. — Allon Guralnek, Jul 12 '12 at 14:04

score 3 · Answer 1 · answered Jul 12 '12 at 13:35

Not sure what you really want, but you can use an anonymous function that will hold this extra variable inside its scope:

a += new A( s => { 
    string extra_value = i.ToString();
    return SomeFunc(s, extra_value);
  });

Which can be simplified into this:

a += s => SomeFunc(s, i.ToString());

score 0 · Answer 2 · edited May 23 '17 at 11:56

Yes you can do this via labda expressions and closures.

The example below will create add delegates to a that will call SomeFunc with the value of i at the time of the loop. The variable capture is needed to ensure that the correct value is captured - see How to tell a lambda function to capture a copy instead of a reference in C#?

public event Action<string> a;

public void AddToDelegate()
{
    for (int i = 0; i < DelegateList.Length; i++)
    {
        int capture = i;
        a += () => SomeFunc(capture.ToString());
    }
}

public string GetData()
{
    StringBuilder _sb = new StringBuilder();
    if (a != null)
    {
        Delegate[] DelegateList = a.GetInvocationList();
        for (int i = 0; i < DelegateList.Length; i++)
        {
            _sb.Append((Action<string>)DelegateList[i]());
        }
    }
    return _sb.ToString();
}

Still need to fix the mess passes to sb.Append(). – H H Jul 12 '12 at 14:06 — H H, Jul 12 '12 at 14:06

Pass parameter to delegate c#

2 Answers2