What are Multicast Delegates in C#?
💡 Concept: Multicast Delegate
A multicast delegate in C# is a delegate that can point to and invoke more than one method in a single call. It is commonly used in event handling where multiple subscribers need to respond to the same event.
📘 Quick Intro
Multicast delegates allow you to assign multiple methods to a single delegate instance using `+` or `+=` operators. When the delegate is invoked, all the methods in its invocation list are executed sequentially.
🧠 Analogy
Think of a multicast delegate like a group email. When you send a message to the group (delegate), everyone in the group (methods) receives it. All the recipients are notified in the order they were added.
🔧 Technical Explanation
- 🔗 A multicast delegate maintains an invocation list of methods to be executed.
- ➕ Use `+=` to add methods and `-=` to remove them.
- ⏱ All methods are called in the order they were added.
- 🚫 Return values are ignored except for the last method in the chain.
- ⚠️ If any method in the chain throws an exception, subsequent methods are not called unless explicitly handled.
🎯 Use Cases
- ✅ Event notification to multiple subscribers.
- ✅ Broadcasting messages to several components.
- ✅ Triggering multiple logging mechanisms.
- ✅ Performing multiple tasks based on a single action.
💻 Code Example
// Declare delegate
public delegate void Notify();
// Define methods
public class Alerts {
public void SendSMS() => Console.WriteLine("SMS sent");
public void SendEmail() => Console.WriteLine("Email sent");
}
public class Program {
public static void Main() {
Alerts alert = new Alerts();
Notify notify = alert.SendSMS;
notify += alert.SendEmail;
notify(); // Calls both methods
}
}
❓ Interview Q&A
Q1: What is a multicast delegate?
A: It’s a delegate that can call multiple methods in a sequence.
Q2: How do you add a method to a multicast delegate?
A: Using `+=` operator.
Q3: Can multicast delegates return multiple values?
A: No, only the return value of the last method is considered.
Q4: Are multicast delegates thread-safe?
A: Not inherently; use locks or concurrent patterns to make them thread-safe.
Q5: What happens if a method in the invocation list throws an exception?
A: It halts execution unless handled.
Q6: How do you remove a method from a multicast delegate?
A: Use `-=` operator.
Q7: Can static methods be used in multicast delegates?
A: Yes, both instance and static methods can be used.
Q8: Can you use anonymous methods with multicast delegates?
A: Yes, and lambdas as well.
Q9: Are events based on multicast delegates?
A: Yes, events use multicast delegates underneath.
Q10: Can delegates be used with async methods?
A: Yes, but invoking them must be handled properly for async execution.
📝 MCQs
Q1. What is a multicast delegate?
- A sealed delegate
- A delegate with return value
- A delegate that can call multiple methods
- None
Q2. Which operator is used to add methods to a multicast delegate?
- +
- ++
- +=
- add()
Q3. What does a multicast delegate store?
- One method
- Class instances
- Invocation list of methods
- Thread references
Q4. What is returned from a multicast delegate?
- All values
- First value
- Return value of the last method
- Null
Q5. What happens when a method throws exception in a multicast delegate?
- Continues silently
- It halts further execution unless handled
- Skips the method
- Logs error
Q6. How do you remove a method from a multicast delegate?
- --
- -=
- remove()
- None
Q7. Are multicast delegates used in events?
- No
- Yes
- Sometimes
- Only in WinForms
Q8. Which is true about multicast delegate?
- Only static methods allowed
- Executes methods in reverse
- Executes methods in order added
- No return value
Q9. Which .NET class represents all delegates?
- System.Object
- System.Func
- System.Delegate
- System.Base
Q10. Can you use multicast delegates with lambda expressions?
- No
- Yes
- Only in .NET 7+
- Not recommended
💡 Bonus Insight
Multicast delegates make it easy to implement observer patterns, where multiple components react to a single event or trigger. They are also great for modular designs where logic can be added or removed without changing the core system.
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