Curriculum
Events, Event Handlers, Lambda Expressions, and Anonymous Methods in C# are advanced programming concepts that enable event-driven development, cleaner code, loose coupling, and modern software architecture. Events, Event Handlers, Lambda Expressions, and Anonymous Methods in C# are widely used in ASP.NET Core Applications, Windows Applications, Desktop Software, Web APIs, Cloud Applications, Game Development, Mobile Applications, and Enterprise Software Systems.
Understanding Events, Event Handlers, Lambda Expressions, and Anonymous Methods in C# is essential because they form the foundation of modern .NET development, asynchronous programming, user interface programming, and LINQ.
An Event in C# is a mechanism that allows one object to notify other objects when a specific action occurs.
Real-world examples:
Button Click
User Login
Order Created
Payment Completed
File Uploaded
Email ReceivedEvents help applications respond automatically to important actions.
Events in C# help developers:
Events are heavily used throughout the .NET ecosystem.
Consider a YouTube channel.
Channel Owner → Publisher
Subscribers → ListenersWhen a new video is uploaded:
Event OccursSubscribers automatically receive notifications.
Events in C# work similarly.
Events follow a Publisher-Subscriber architecture.
Publisher:
Raises EventSubscriber:
Handles EventExample:
Button → Publisher
Application Logic → SubscriberThis architecture is common in enterprise applications.
Events are declared using delegates.
Syntax:
public delegate void
MyDelegate();Event:
public event MyDelegate
MyEvent;The event can now notify subscribers.
Publisher:
public class Process
{
public delegate void
ProcessCompletedHandler();
public event
ProcessCompletedHandler
ProcessCompleted;
public void Start()
{
Console.WriteLine(
"Processing");
ProcessCompleted?.Invoke();
}
}Subscriber:
public class Notification
{
public void ShowMessage()
{
Console.WriteLine(
"Process Completed");
}
}Usage:
Process process =
new Process();
Notification notification =
new Notification();
process.ProcessCompleted +=
notification.ShowMessage;
process.Start();Output:
Processing
Process CompletedThe event automatically notifies the subscriber.
Subscribing:
process.ProcessCompleted +=
notification.ShowMessage;Meaning:
Register Event HandlerThe subscriber begins listening for the event.
Removing subscription:
process.ProcessCompleted -=
notification.ShowMessage;Meaning:
Stop ListeningThis prevents further notifications.
.NET provides a built-in delegate:
EventHandlerInstead of:
public delegate void
MyDelegate();developers often use:
public event EventHandler
MyEvent;This is the standard .NET approach.
Publisher:
public event EventHandler
OrderPlaced;Raise Event:
OrderPlaced?.Invoke(
this,
EventArgs.Empty);Subscriber:
public void Notify(
object sender,
EventArgs e)
{
Console.WriteLine(
"Order Received");
}This pattern is used throughout .NET.
Sometimes additional data must be passed.
Example:
public class OrderEventArgs :
EventArgs
{
public int OrderId
{
get;
set;
}
}Event:
public event
EventHandler<OrderEventArgs>
OrderPlaced;Raise Event:
OrderPlaced?.Invoke(
this,
new OrderEventArgs
{
OrderId = 1001
});Custom event data improves flexibility.
Lambda Expressions provide a concise way to write anonymous functions.
Syntax:
(parameter) =>
expressionExample:
x => x * 2Meaning:
Input x
Return x * 2Lambda Expressions are heavily used in LINQ and Delegates.
Traditional Method:
public static int Add(
int a,
int b)
{
return a + b;
}Lambda:
Func<int,int,int>
add =
(a,b) =>
a + b;Usage:
Console.WriteLine(
add(10,20));Output:
30The lambda version is shorter and cleaner.
Example:
List<int> numbers =
new List<int>
{
10,
20,
30,
40
};LINQ:
var result =
numbers.Where(
n => n > 20);Output:
30
40This is one of the most common LINQ patterns.
Example:
Func<int,int,int>
add =
(a,b) =>
{
int result =
a + b;
return result;
};Output:
30Complex logic can be included.
Example:
button.Click +=
(sender,e) =>
{
Console.WriteLine(
"Button Clicked");
};Output:
Button ClickedThis is common in desktop and web development.
Anonymous Methods are methods without names.
Before Lambda Expressions, anonymous methods were commonly used.
Syntax:
delegate
{
}Example:
Action display =
delegate
{
Console.WriteLine(
"Hello");
};Usage:
display();Output:
HelloAnonymous methods simplify temporary logic.
Example:
Action<string> display =
delegate(string name)
{
Console.WriteLine(
name);
};Usage:
display("Rahul");Output:
RahulParameters can be passed normally.
Anonymous Method:
delegate(int x)
{
return x * 2;
}Lambda Expression:
x => x * 2Lambda expressions are more concise and widely preferred.
Event-driven systems respond automatically to actions.
Examples:
Button Click
Order Created
Payment Successful
Email Received
File UploadedMost modern applications use event-driven architecture.
Publisher:
Order ServiceSubscribers:
Email Service
SMS Service
Inventory ServiceEvent:
OrderPlacedWhen an order is placed:
Send Email
Send SMS
Update InventoryEvents make this architecture possible.
Transaction Notifications
Balance Alerts
Fraud Detection EventsOrder Events
Payment Events
Shipping NotificationsAppointment Notifications
Patient Alerts
Medical UpdatesAttendance Alerts
Exam Notifications
Fee RemindersEvents improve automation significantly.
Components remain independent.
Code becomes easier to manage.
Logic can be reused.
Lambda expressions reduce code length.
Applications become more responsive.
These benefits are essential for enterprise applications.
Can cause memory leaks.
May reduce readability.
Always verify events before invoking.
Example:
MyEvent?.Invoke();Keep lambdas simple and readable.
An Event is a mechanism used to notify subscribers when an action occurs.
EventHandler is the built-in delegate used for events.
A Lambda Expression is a concise anonymous function.
An Anonymous Method is a method without a name.
Events enable event-driven programming and loose coupling.
Lambda Expressions simplify delegates and LINQ queries.
Events are mechanisms for notifying subscribers when specific actions occur.
EventHandler is the standard delegate used for .NET events.
A Lambda Expression is a compact anonymous function.
An Anonymous Method is a method without a declared name.
Lambda Expressions are shorter, cleaner, and easier to read.
They enable event-driven programming, cleaner code, LINQ, callbacks, and scalable software architecture.