How to use IEnumerable/IEnumerator

Introduction

IEnumerable is an interface, implemented by System.Collecetion type in .Net that provides iterator pattern. The definition according to MSDN is:

“Exposes the enumerator, which supports simple iteration over non-generic collection.”

It’s something that you can loop over. That might be a List or Array or anything else that supports foreach loop.

Objective

Explore usage of IEnumerable and IEnumerator for user defined class.

Description

Let’s first show how both IEnumerable and IEnumerator works: Let’s define List of string and iterate each element using iterator pattern

// This is a collection that eventually we will use an Enumertor to loop through
// rather than a typical index number if we used a for loop.
List<string> Oceans = new List<string>();

Oceans.Add("Pacific");
Oceans.Add("Atlantic");
Oceans.Add("Indian");
Oceans.Add("Southern");
Oceans.Add("Arctic");

Now, we already knows how to iterate each element using foreach loop 

// HERE is where the Enumerator is gotten from the List<string> object

foreach(string ocean in Oceans)

{
    Console.WriteLine(ocean);
} 

// We can do same thing using IEnumerable/IEnumerator.

 IEnumerator enumerator = Oceans.GetEnumerator();

while(enumerator.MoveNext())
{
    string ocean = Convert.ToString(enumerator.Current);
    Console.WriteLine(ocean);
}