Action delegate type in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Action delegate type

Define Action delegate

↓

Assign method or lambda

↓

Invoke Action

↓

Execute method body

↓

Finish

The Action delegate holds a method reference with no return value and can be invoked to run that method.

Execution Sample

C Sharp (C#)

Action<string> greet = name => Console.WriteLine($"Hello, {name}!");
greet("Alice");

Defines an Action delegate that prints a greeting and then calls it with "Alice".

Execution Table

Step	Action	Evaluation	Result
1	Define Action delegate 'greet'	Action<string> greet = lambda	greet holds reference to lambda
2	Invoke greet with "Alice"	greet("Alice")	Calls lambda with name="Alice"
3	Execute lambda body	Console.WriteLine($"Hello, {name}!")	Prints: Hello, Alice!
4	End of program	No more code	Program finishes

💡 Program ends after greet is invoked and message printed

Variable Tracker

Variable	Start	After 1	After 2	Final
greet	null	lambda reference	lambda reference	lambda reference
name	undefined	undefined	"Alice"	undefined after call

Key Moments - 3 Insights

Why does the Action delegate not return any value?

Action delegates are designed to represent methods that return void, so no value is returned when invoked, as shown in execution_table step 3.

How does the lambda expression relate to the Action delegate?

The lambda expression is assigned to the Action delegate variable 'greet' at step 1, meaning 'greet' holds the method to run when invoked.

What happens to the parameter 'name' after the Action is invoked?

The parameter 'name' exists only during the call (step 3) and is not stored afterward, as seen in variable_tracker where 'name' is undefined before and after invocation.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what does the Action delegate do?

A Prints a greeting message

B Returns a string value

C Throws an error

D Changes the value of 'greet'

💡 Hint

Check execution_table row 3 under Result column for what happens during invocation

According to variable_tracker, what is the value of 'greet' after step 1?

A null

B lambda reference

C undefined

D "Alice"

💡 Hint

Look at variable_tracker row for 'greet' after 1

At which step does the program finish execution?

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

See execution_table exit_note and step 4 description

Concept Snapshot

Action delegate type:
- Represents a method with no return value (void)
- Can take parameters (e.g., Action<string>)
- Assigned with method or lambda
- Invoked like a method
- Used for callbacks or simple actions

Full Transcript

This example shows how to use the Action delegate type in C#. First, an Action delegate named 'greet' is defined and assigned a lambda expression that takes a string parameter 'name' and prints a greeting. When 'greet' is invoked with the argument "Alice", the lambda runs and prints "Hello, Alice!". The Action delegate does not return any value. Variables like 'greet' hold the method reference, and 'name' exists only during the call. The program ends after the Action is invoked and the message is printed.