How to pass a function as a parameter in C#?

c# reflection

Is it possible to pass a function as a parameter in C#? I can do it using the Func or Action classes, but this forces me to declare the entire function signature at once. When I try to use Delegate, I get a compile error saying it can't convert a method group to a Delegate.

I'm working on Axial and I'm trying to allow users to call web services. What I'm going for is the ability to create the Visual Studio proxy class and then pass in the generated function. The function signature doesn't matter because the generated code only uses the function name. However, I'd like to pass in the function instead of the name for two reasons: the ability to use the proxy's Url property and a compiler error if the web service doesn't exist or is updated in Visual Studio.


public void AlertIt(object o) {
    Axial.DOM.Window.Alert(o.ToString());
}
public void CallAddService() {
    object[] param = new object[] { int.Parse(txtA.Text), int.Parse(txtB.Text) };
    Axial.ServerScript.CallWebService(new WSProxy.WS().Add, param, AlertIt, AlertIt);
}

class Axial.ServerScript {
    public void CallWebService(Delegate method, object[] param, Action<object> successCallback, Action<object> failureCallback) {
        // translate to javascript (already working)
    }
}

I think what you want is:

static object InvokeMethod(Delegate method, params object[] args){
    return method.DynamicInvoke(args);
}

static int Add(int a, int b){
    return a + b;
}

static void Test(){
    Console.WriteLine(InvokeMethod(new Func<int, int, int>(Add), 5, 4));
}

Prints "9".

Converting a method group, anonymous method or lambda expression to a delegate requires the compiler to know the exact delegate type. However, you could potentially use lambda expressions and captured variables to make this simpler:

public void InvokeMethod(Action action)
{
    action();
}

public int Add(int a, int b)
{
    return a + b;
}

public void Test()
{    
    InvokeMethod(() => Add(2, 3));
}

That basically delays invocation in the normal way, but by wrapping the actual call to Add in a plain Action delegate.

If that doesn't fulfil your requirements, perhaps you can tell us a bit more about what you're really trying to achieve.

EDIT: If this is generated code, you can cast to a Func<...> with the right type arguments - assuming there aren't too many. Other than that, there's no real way of just passing in a method group. There's been occasional calls for an "infoof(...)" operator (like typeof but for members) which would give you a MemberInfo, but that doesn't actually exist.

How to pass a function as a parameter in C#?

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