Difference Between Delegate and Event in C#
💡 Concept: Delegate vs Event
Delegates are function pointers in C#, while events are wrappers around delegates that enforce encapsulation and are used to signal that something has occurred.
📘 Quick Intro
Delegates allow methods to be assigned and invoked dynamically. Events are built on top of delegates and are commonly used in publish-subscribe scenarios like GUI event handling.
🧠 Analogy
Think of a delegate as a phone number—you can call it directly. An event is like a doorbell—you can press it (trigger), but you can't control what happens on the other side. Delegates provide direct access; events provide controlled access.
🔧 Technical Explanation
- 🔗 A delegate is a reference type that points to methods with a specific signature.
- 🔒 An event uses a delegate internally but restricts invocation to the declaring class only.
- 👥 Delegates support multicast; events typically wrap multicast delegates.
- 🛑 You can invoke a delegate from anywhere, but not an event.
- 📦 Events provide better encapsulation and abstraction in publish-subscribe design.
🎯 Use Cases
- ✅ Use delegates for callbacks, method chaining, and dynamic method invocation.
- ✅ Use events for notifying multiple subscribers when something happens.
- ✅ Events are common in UI frameworks like WinForms or WPF.
- ✅ Delegates are used for designing extensible plugins and LINQ expressions.
💻 Code Example
// Delegate
public delegate void Notify(string msg);
public class DelegateDemo {
public Notify NotifyDelegate;
public void Call() {
NotifyDelegate("Delegate called.");
}
}
// Event
public class EventDemo {
public event Notify NotifyEvent;
public void Trigger() {
NotifyEvent?.Invoke("Event triggered.");
}
}
❓ Interview Q&A
Q1: What is a delegate?
A: It's a type that references methods with a specific signature.
Q2: What is an event?
A: It's a mechanism for communication between objects, based on delegates.
Q3: Can you invoke a delegate outside its class?
A: Yes.
Q4: Can you invoke an event outside its class?
A: No, only the declaring class can trigger the event.
Q5: Do events support multicast?
A: Yes, through multicast delegates.
Q6: Why are events safer than delegates?
A: Events encapsulate the delegate and prevent external modification.
Q7: What is a common use case for delegates?
A: Callbacks and custom logic injection.
Q8: What is a common use case for events?
A: GUI button clicks and observer patterns.
Q9: Are events a type of delegate?
A: Yes, they are built on delegates.
Q10: Can multiple handlers subscribe to an event?
A: Yes, using += syntax.
📝 MCQs
Q1. Which keyword is used to declare an event?
- delegate
- event
- signal
- call
Q2. Which can be invoked from outside the class?
- event
- delegate
- both
- none
Q3. Which provides encapsulation?
- delegate
- event
- method
- constructor
Q4. Which is preferred for callbacks?
- event
- delegate
- interface
- class
Q5. Which supports multicast?
- delegate
- event
- Both
- None
Q6. What prevents misuse of delegate by consumers?
- interface
- abstract
- event
- readonly
Q7. Which is better for publishing notifications?
- delegate
- event
- static
- field
Q8. How to subscribe to an event?
- Using call()
- Using +=
- Using invoke()
- With override
Q9. Are delegates type-safe?
- No
- Yes
- Only in events
- Only if static
Q10. Which is restricted to its declaring class?
- event
- delegate
- method
- abstract class
💡 Bonus Insight
Use delegates when you need flexibility and dynamic behavior, like passing methods as parameters. Use events when you want to enforce controlled notifications to subscribers without exposing implementation logic.
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