C# 5.0 Programmer's Reference

164 ❘ CHAPTER 7 Program Control Statements
This code creates an enumerator to enumerate over Employee objects. It then enters a while loop.
If enumerator.MoveNext returns true, the enumerator has successfully moved to the next object
in the collection. As long as it has read an object, the program uses enumerator.Current to get the
current object and displays that object’s Name property in the Console window.
When it reaches the end of the employees list, the enumerator’s MoveNext method returns false
and the loop ends.
A foreach loop provides roughly the same access to the items in a container class as an enumerator.
Under some circumstances, however, an enumerator may provide a more natural way to loop through
a container class than a foreach loop. For example, an enumerator can skip several items without
examining them closely. You can also use an enumerator’s Reset method to restart the enumeration.
To restart a foreach loop, you would need to start the loop over.
The IEnumerable interface defines the features needed for enumerators, so any class that implements
the IEnumerable interface provides enumerators. Any class that supports foreach must also implement
the IEnumerable interface, so any class that supports foreach also supports enumerators. A few
of the classes that implement IEnumerable include the following:
Array HybridDictionary SqlDataReader
ArrayList ListDictionary Stack
Collection MessageQueue String
CollectionBase OdbcDataReader StringCollection
ControlCollection OleDbDataReader StringDictionary
DataView OracleDataReader TableCellCollection
DictionaryBase Queue TableRowCollection
DictionaryEntries ReadOnlyCollectionBase XmlNode
Hashtable SortedList XmlNodeList
Iterators
An iterator is similar in concept to an enumerator. It also provides methods that enable you to step
through the items in some sort of container object. Iterators are more specialized than enumerators
and work with particular classes.
For example, a GraphicsPath object represents a series of connected lines and curves.
A GraphicsPathIterator object can step through the line and curve data contained in a
GraphicsPath object.
Iterators are much more specialized than enumerators. How you use them depends on what you
need to do and on the kind of iterator, so they are not described in detail here.
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