Question

I’m been wanting to create a user control, but before I do I need to know how to do a few things or even if its possible. I know it possible to pass a method to a function (Link). Is it possible to set a variable that is of function type? For example I have a user control where in one function I need to call GetData function. Each GetData routine is different so I was wondering if its possible to pass that function in from the aspx.cs page?

Answer 1

The .NET Framework Library defines handy generic delegates (or “function types” as you call it). Function delegates that have a return value

Func<Ret>
Func<Arg, Ret>
Func<Arg1, Arg2, Ret>
...

Function delegates that have no return value

Action<>
Action<Arg>
Action<Arg1, Arg2>
...

You can define a method that accepts a delegate like this

void DrawFunction(Func<double, double> function, double x0, double x1)
{
    const double step = 0.1;

    for (x = x0; x <= x1; x += step) {
        double y = function(x);
        DrawPointAt(x, y);
    }
}

---

You can call it by either passing it an appropriate method or with a lambda expression.

Using this declaration

public double Square(double x)
{
    return x*x;
}

You can do the call (note that the parentheses () are missing after Square since we do not want to call this method here)

DrawFunction(Square, 0.0, 10.0);

You get the same result with a lambda expression

DrawFunction(x => x*x, 0.0, 10.0);