Sequentially access the elements of a collection.
The Iterator pattern provides a way of accessing elements of a collection
sequentially, without knowing how the collection is structured. As an extension,
the pattern allows for filtering elements in a variety of ways as they are
generated.
Provide a way to access the elements of an aggregate object sequentially without
exposing its underlying representation.
Design
The concept of iterators and enumerators (also called generators) has been
around for a long time. Enumerators are responsible for producing the next
element in a sequence defined by certain criteria. Such a sequence is said to be
enumerable. Examples might be the next prime number or the next product order
sorted by date. The iterator is the means by which we cycle through this
sequence of elements from beginning to end.
UML Diagram
C# support for the pattern
public class Person
{
public string
FirstName { get; set;
}
public string
LastName { get; set;
}
}
public class People :
IEnumerable
{
private
Person[] _person;
public People(Person[]
person)
{
_person = new Person[person.Length];
for (int i = 0;
i < person.Length; i++)
_person[i] = person[i];
}
public IEnumerator
GetEnumerator()
{
foreach (Person
p in _person)
yield return p; //Yield return value to the Enumerator
object.
}
}
static void Main(string[]
args)
{
Person[] peopleArray =
new Person[3]
{
new
Person(){ FirstName= "Chinna", LastName = "Srihari"},
new
Person(){ FirstName= "Chinna", LastName="Sushma"},
new
Person() { FirstName= "Chinna",
LastName= "Lohetha"},
};
People p = new People(peopleArray);
foreach (Person
p1 in p)
Console.WriteLine(p1.FirstName
+ ", " + p1.LastName);
}