Action Delegate in C#

In C#, Action is a built-in generic delegate type that represents a method that does not return a value. It is used when you only need to perform an action but don’t need a result back.

• Defined in the System namespace.
• Can take zero to sixteen input parameters.
• Always returns void.
• If a delegate should return a value, use Func instead.

Syntax:

Action<T1, T2, ...> variableName = method_or_lambda;

• T1, T2, ... : Input parameter types.
• No return type parameter because Action always returns void.

Example 1: Action with No Parameters

An Action delegate can represent a method that takes no parameters and returns nothing.

Action greet = () => Console.WriteLine("Hello from Action!");
greet();

Output:

Hello from Action!

Here greet is an Action delegate with no parameters. When invoked, it simply executes the lambda expression and prints a message.

Example 2: Action with One Parameter

You can define Action delegates that accept input parameters.

Action<string> printMessage = msg => Console.WriteLine(msg);
printMessage("Welcome to C# Action delegates");

Output:

Welcome to C# Action delegates

This Action takes a single string parameter and prints it. The delegate type is Action<string> because it accepts one string input.

Example 3: Action with Two Parameters

Action delegates can handle multiple input parameters (up to 16).

Action<int, int> displaySum = (a, b) => Console.WriteLine($"Sum: {a + b}");
displaySum(5, 8);

Output:

Sum : 13

The delegate accepts two integers and prints their sum. No return value is expected because Action always returns void.

Example 4: Action with Multiple Statements

You can use braces {} if more logic is needed.

Action<string> processName = name => {
    string upper = name.ToUpper();
    Console.WriteLine($"Processed Name: {upper}");
};
processName("john");

Output:

Processed Name: JOHN

This Action takes a string input, converts it to uppercase and then prints it. The block body allows adding extra steps inside the delegate.

Example 5: Action with Named Method

You can assign an Action delegate to a method.

class Program {
    static void ShowMessage(string msg) {
        Console.WriteLine(msg);
    }

    static void Main() {
        Action<string> action = ShowMessage;
        action("Hello using named method");
    }
}

Output:

Hello using named method

Here the ShowMessage method matches the Action<string> delegate signature, so it can be assigned directly and invoked using the delegate.

Example 6: Action with Collections (LINQ)

Action is often used in ForEach loops with collections.

List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };

numbers.ForEach(n => Console.WriteLine($"Number: {n}"));

Output:

Number: 1

Number: 2

Number: 3

Number: 4

Number: 5

The ForEach method expects an Action delegate. Here, each element of the list is passed to the Action, which prints the number to the console.

Suggested Quiz

Edit Quiz

4 Questions

Which of the following statements about Action delegates is correct?

• A

  Action delegates return a value.

• B

  Action delegates are not defined in System namespace.

• C

  Action delegates cannot take input parameters.

• D

  Action delegates always return void.

Explanation:

Which of the following is true about the difference between Func and Action delegates?

• A

  Func always returns void, Action can return a value.

• B

  Func cannot be used with LINQ, Action can be used.

• C

  Func can have up to 16 input parameters and always returns a value, Action can have up to 16 input parameters and returns void.

• D

  Func cannot point to named methods, Action can.

Explanation:

Func returns a value, Action does not. Both can have up to 16 input parameters.

What will be the output of the following C# code?

C#

using System;

class Program
{
    static void Main()
    {
        Action<string> show = msg => Console.WriteLine(msg.Length);
        show("Action");
    }
}

• A

  Action

• B

  5

• C

  6

• D

  Compile-time error

Explanation:

The string "Action" has 6 characters.

The Action<string> delegate executes the lambda and prints the length of the string, not the string itself.

What will be printed when the following code is executed?

C#

using System;

class Program
{
    static void Print(int a, int b)
    {
        Console.WriteLine(a * b);
    }

    static void Main()
    {
        Action<int, int> act = Print;
        act(4, 5);
    }
}

• A

  9

• B

  20

• C

  45

• D

  No output

Explanation:

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