What is a Delegate in C#?
💡 Concept: Delegate
A delegate in C# is a type-safe function pointer that encapsulates a method with a specific signature. Delegates enable callback mechanisms, event-driven programming, and functional programming styles by allowing methods to be passed as parameters.
📘 Quick Intro
Delegates act like references to functions. They are useful when you want to pass methods as arguments, trigger methods dynamically, or support events and asynchronous patterns in your application.
🧠 Analogy
Think of a delegate like a remote control. The remote (delegate) doesn’t know the exact TV brand (method), but it can call the correct signal as long as the interface (method signature) matches. You press a button, and something happens — that’s the power of delegates calling methods dynamically.
🔧 Technical Explanation
- 🧩 A delegate defines a method signature and can hold references to methods matching that signature.
- 🔗 Delegates are reference types derived from `System.Delegate`.
- 🎯 Commonly used with events and callbacks in asynchronous or GUI applications.
- 🔄 Multicast delegates can call multiple methods in a chain.
- 🚀 Supports both synchronous and asynchronous execution using `BeginInvoke` and `EndInvoke` (older model).
🎯 Use Cases
- ✅ Callback functions (e.g., after a task completes).
- ✅ Event handling in UI frameworks like WinForms or WPF.
- ✅ Strategy pattern implementations (behavior passed as delegates).
- ✅ Plug-in architectures where behavior is injected.
- ✅ LINQ and lambda expressions use delegates under the hood.
💻 Code Example
// Define a delegate
public delegate void PrintMessage(string message);
public class Messenger {
public void Show(string msg) {
Console.WriteLine(""Message: "" + msg);
}
}
public class Program {
public static void Main() {
Messenger m = new Messenger();
PrintMessage pm = new PrintMessage(m.Show);
pm(""Hello from delegate!"");
}
}
❓ Interview Q&A
Q1: What is a delegate in C#?
A: A delegate is a type-safe object that points to methods with a specific signature.
Q2: Why are delegates useful?
A: They allow methods to be passed as parameters, supporting event handling and callbacks.
Q3: Can a delegate point to multiple methods?
A: Yes, that’s called a multicast delegate.
Q4: Are delegates reference or value types?
A: Delegates are reference types.
Q5: What is the base class for all delegates?
A: System.Delegate.
Q6: How are events related to delegates?
A: Events are built on top of delegates in C#.
Q7: Can you use anonymous methods with delegates?
A: Yes, and also lambda expressions.
Q8: What's the difference between delegate and event?
A: A delegate can call methods; an event uses a delegate but controls access.
Q9: Can delegates be chained?
A: Yes, multiple methods can be invoked via a single delegate instance.
Q10: Are delegates only used in GUIs?
A: No, they are useful in callbacks, async, LINQ, and design patterns.
📝 MCQs
Q1. What is a delegate in C#?
- A variable
- A function
- A type-safe function pointer
- A constructor
Q2. Which class is the base of all delegates?
- System.Object
- System.Function
- System.Action
- System.Delegate
Q3. What is multicast delegate?
- Used in multithreading
- Returns multiple values
- A delegate that can point to multiple methods
- Used in networking
Q4. Are delegates reference or value types?
- Value types
- Reference types
- Structs
- Enums
Q5. Which keyword is used to declare a delegate?
- event
- handler
- callback
- delegate
Q6. Can a delegate point to a static method?
- Yes
- No
- Only instance methods
- Only abstract methods
Q7. How do delegates relate to events?
- They are same
- No relation
- Delegates use events
- Events are built on delegates
Q8. Which of these can be used with delegates?
- Objects
- Lambda expressions
- Threads
- Exceptions
Q9. Can you pass a delegate as an argument?
- No
- Yes
- Only for static methods
- Only with events
Q10. What does delegate encapsulate?
- Class reference
- Constructor
- Method reference
- None
💡 Bonus Insight
Delegates are foundational in event-driven and functional programming in C#. They empower developers to write cleaner, more modular, and reusable code. Understanding delegates helps in mastering LINQ, event handling, and even async programming.
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