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Iterator Design Pattern - C#

  Author : Shailendra Chauhan
Posted On : 23 Feb 2017
Total Views : 4,767   
Updated On : 23 Feb 2017

Iterator Design Pattern falls under Behavioral Pattern of Gang of Four (GOF) Design Patterns in .Net. The command pattern is commonly used in the menu systems of many applications such as Editor, IDE etc. In this article, I would like share what is iterator pattern and how is it work?

What is Iterator Design Pattern?

This pattern is provides a way to access the elements of a collection object in sequential manner without knowing its underlying structure.

This pattern is commonly used in the menu systems of many applications such as Editor, IDE etc.

Iterator Design pattern - UML Diagram & Implementation

The UML class diagram for the implementation of the Iterator Design pattern is given below:

Iterator Design Pattern C#

The classes, interfaces and objects in the above UML class diagram are as follows:

  1. Client

    This is the class that contains an object collections and uses Next operation of the iterator to retrieve items from the aggregate in an appropriate sequence.

  2. Iterator

    This is an interface that defines operations for accessing the collection elements in a sequence.

  3. ConcreteIterator

    This is a class that implements Iterator interface.

  4. Aggregate

    This is an interface which defines an operation to create an iterator.

  5. ConcreteAggregate

    This is a class that implements Aggregate interface.

C# - Implementation Code

public class Client
 public void UseIterator()
 ConcreteAggregate aggr = new ConcreteAggregate();

 Iterator iterator = aggr.CreateIterator();
 while (iterator.Next())
 string item = (string)iterator.Current;

public interface Aggregate
 Iterator CreateIterator();

public class ConcreteAggregate : Aggregate
 private ArrayList items = new ArrayList();

 public Iterator CreateIterator()
 return new ConcreteIterator(this);

 public object this[int index]
 get { return items[index]; }

 public int Count
 get { return items.Count; }

 public void Add(object o)
public interface Iterator
 object Current { get; }
 bool Next();


public class ConcreteIterator : Iterator
 private ConcreteAggregate aggregate;
 int index;

 public ConcreteIterator(ConcreteAggregate aggregate)
 this.aggregate = aggregate;
 index = -1;

 public bool Next()
 return index < aggregate.Count;

 public object Current
 if (index < aggregate.Count)
 return aggregate[index];
 throw new InvalidOperationException();

Real Life Example:

Real Life Example of Iterator Design Pattern C#

When to use it?

  1. Allows to access the elements of a collection object in sequential manner without knowing its underlying structure.

  2. Multiple or concurrent iterations are required over collections elements.

  3. Provides a uniform interface for accessing the collection elements.

What do you think?

I hope you will enjoy the Iterator Design Pattern while designing your software. I would like to have feedback from my blog readers. Your valuable feedback, question, or comments about this article are always welcome.


Shailendra Chauhan
Author, Architect, Corporate Trainer and Microsoft MVP

He is the author of some of most popular e-books which encompass technical Interview on Node.js Interview Questions and Answers, ASP.NET MVC Interview Questions and Answers, AngularJS Interview Questions and Answers and LINQ Interview Questions and AnswersKnow more...

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