Delegates as callback pattern in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a delegate in C#?

A delegate is a type that holds references to methods with a specific signature. It allows methods to be passed as parameters or assigned to variables.

beginner

How does a delegate enable the callback pattern?

A delegate lets you pass a method as an argument to another method. The receiving method can then call the passed method later, acting as a callback.

intermediate

Show a simple example of a delegate used as a callback.

public delegate void Notify(string message);

public class Process {
    public void Start(Notify callback) {
        // Do some work
        callback("Process finished");
    }
}

// Usage
Process p = new Process();
p.Start(msg => Console.WriteLine(msg));

intermediate

What is the benefit of using delegates for callbacks?

Delegates provide flexibility by allowing different methods to be called without changing the caller code. This supports loose coupling and reusable code.

advanced

Can delegates point to multiple methods? What is this called?

Yes, delegates can point to multiple methods. This is called a multicast delegate. When invoked, all methods are called in order.

What does a delegate in C# represent?

A A class that inherits from another class

B A variable that stores data

C A type of loop

D A reference to a method with a specific signature

A delegate holds references to methods matching its signature, enabling callbacks.

How do delegates support the callback pattern?

A By creating new classes dynamically

B By storing data in arrays

C By allowing methods to be passed as parameters and called later

D By running code in parallel automatically

Delegates let you pass methods as arguments, which can be called back later.

What keyword is used to declare a delegate in C#?

A function

B delegate

C callback

D event

The 'delegate' keyword declares a delegate type.

What happens when a multicast delegate is invoked?

A All methods assigned to it are called in order

B Only the first method is called

C It throws an error

D It returns a list of methods

Multicast delegates call all their assigned methods sequentially.

Which of these is a benefit of using delegates for callbacks?

A They allow loose coupling between caller and callee

B They increase program size significantly

C They prevent any method from being called

D They make code run slower always

Delegates enable loose coupling by letting different methods be called without changing the caller.

Explain how delegates enable the callback pattern in C#.

Think about how you can give a method to another method to call back.

Describe the difference between a single-cast and multicast delegate.

Consider how many methods a delegate can point to.