C# - 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.