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.

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.

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).

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.

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.

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.

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.