What is this delegate method doing?

Question

I've been reading the MSDN page on delegates and they seem straightforward. Then I was looking at some code that uses them and I saw this:

 public delegate void NoArguments();
 public NoArguments Refresh = null;
 Refresh = new NoArguments( Reset );

It's that third line that confuses me. How can you new a delegate? It is not an object, it's a method, or rather a delegate to a method. According to the example on the MSDN page, creating an instance of a delegate is through simple assignment, not allocaiton. Furthermore, why is the new for the delegate taking a parameter, Reset, when the delegate declaration takes no parameters?

Answer 1

The delegate keyword indicates that what follows is essentially a function signature, so therefore, Refresh becomes kind of like a pointer to a function that takes no arguments. However, to assign something to the Refresh pointer, you have to give it a function to point to. In this case, it's the Reset function. And further, the Reset function must take no arguments.

In addition, the syntax:

Refresh = Reset;

is also valid, and is just syntactic sugar for the more formal syntax:

Refresh = new NoArguments(Reset);

in both cases, you could then execute the Reset function by calling Refresh:

Refresh();

Note, however, that if you execute Refresh() without it having been assigned, then you could generate an exception. The way to prevent this would be to check it against null:

if (Refresh != null) Refresh();
else {
    // Refresh was never assigned
}

Answer 2

You may think delegate is like a function type:

• Declare type, function returns void and have no arguments:

  public delegate void NoArguments();
  

• Declare variable of given type and initialize it:

  public NoArguments Refresh = null;
  

• Assign new object to your variable. Object is actually a function Reset, which must have the same signature as your delegate:

  Refresh = new NoArguments( Reset );
  

UPDATE:

You may review the following link for more details: C# Delegates