Action Delegate:

Action is also a delegate type defined in the System namespace. An Action type delegate is the same as Func delegate except that the Action delegate doesn't return a value. In other words, an Action delegate can be used with a method that has a void return type.

For example, the following delegate prints an int value.

Example: C# Delegate

public delegate void Print(int val);

static void ConsolePrint(int i)
{
    Console.WriteLine(i);
}

static void Main(string[] args)
{           
    Print prnt = ConsolePrint;
    Prnt(10);
}

Output:
10

You can use an Action delegate instead of defining the above Print delegate, for example:

Example: Action delegate

static void ConsolePrint(int i)
{
    Console.WriteLine(i);
}

static void Main(string[] args)
{
    Action<int> printActionDel = ConsolePrint;
    printActionDel(10);
}

You can initialize an Action delegate using the new keyword or by directly assigning a method:


Action<int> printActionDel = ConsolePrint;

//Or

Action<int> printActionDel = new Action<int>(ConsolePrint);

An Action delegate can take up to 16 input parameters of different types.

An Anonymous method can also be assigned to an Action delegate, for example:

Example: Anonymous method with Action delegate

static void Main(string[] args)
{
    Action<int> printActionDel = delegate(int i)
                                {
                                    Console.WriteLine(i);
                                };

    printActionDel(10);
}

Output:
10

A Lambda expression also can be used with an Action delegate:

Example: Lambda expression with Action delegate

static void Main(string[] args)
{

    Action<int> printActionDel = i => Console.WriteLine(i);
       
    printActionDel(10);
}

Thus, you can use any method that doesn't return a value with Action delegate types.

Advantages of Action and Func delegates:

  1. Easy and quick to define delegates.
  2. Makes code short.
  3. Compatible type throughout the application.

Points to Remember :

  1. Action delegate is same as func delegate except that it does not return anything. Return type must be void.
  2. Action delegate can have 1 to 16 input parameters.
  3. Action delegate can be used with anonymous methods or lambda expressions.

Learn about predicate delegate next.