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StringEnumerator Class

Supports a simple iteration over a StringCollection.

For a list of all members of this type, see StringEnumerator Members.

System.Object
   System.Collections.Specialized.StringEnumerator

[Visual Basic]
Public Class StringEnumerator
[C#]
public class StringEnumerator
[C++]
public __gc class StringEnumerator
[JScript]
public class StringEnumerator

Thread Safety

Public static (Shared in Visual Basic) members of this type are safe for multithreaded operations. Instance members are not guaranteed to be thread-safe.

Remarks

Enumerators only allow reading the data in the collection. Enumerators cannot be used to modify the underlying collection.

Initially, the enumerator is positioned before the first element in the collection. Reset also brings the enumerator back to this position. At this position, calling Current throws an exception. Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

Current returns the same object until either MoveNext or Reset is called. MoveNext sets Current to the next element.

After the end of the collection is passed, the enumerator is positioned after the last element in the collection, and calling MoveNext returns false. If the last call to MoveNext returned false, calling Current throws an exception. To set Current to the first element of the collection again, you can call Reset followed by MoveNext.

An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException. If the collection is modified between MoveNext and Current, Current will return the element that it is set to, even if the enumerator is already invalidated.

The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads could still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Example

[Visual Basic, C#, C++] The following code example demonstrates several of the properties and methods of StringEnumerator.

[Visual Basic] 
Imports System
Imports System.Collections.Specialized

Public Class SamplesStringEnumerator

   Public Shared Sub Main()

      ' Creates and initializes a StringCollection.
      Dim myCol As New StringCollection()
      Dim myArr() As [String] = {"red", "orange", "yellow", "green", "blue", "indigo", "violet"}
      myCol.AddRange(myArr)

      ' Enumerates the elements in the StringCollection.
      Dim myEnumerator As StringEnumerator = myCol.GetEnumerator()
      While myEnumerator.MoveNext()
         Console.WriteLine("{0}", myEnumerator.Current)
      End While
      Console.WriteLine()

      ' Resets the enumerator and displays the first element again.
      myEnumerator.Reset()
      If myEnumerator.MoveNext() Then
         Console.WriteLine("The first element is {0}.", myEnumerator.Current)
      End If 

   End Sub 'Main

End Class 'SamplesStringEnumerator 


'This code produces the following output.
'
'red
'orange
'yellow
'green
'blue
'indigo
'violet
'
'The first element is red.


[C#] 
using System;
using System.Collections.Specialized;

public class SamplesStringEnumerator  {

   public static void Main()  {

      // Creates and initializes a StringCollection.
      StringCollection myCol = new StringCollection();
      String[] myArr = new String[] { "red", "orange", "yellow", "green", "blue", "indigo", "violet" };
      myCol.AddRange( myArr );

      // Enumerates the elements in the StringCollection.
      StringEnumerator myEnumerator = myCol.GetEnumerator();
      while ( myEnumerator.MoveNext() )
         Console.WriteLine( "{0}", myEnumerator.Current );
      Console.WriteLine();

      // Resets the enumerator and displays the first element again.
      myEnumerator.Reset();
      if ( myEnumerator.MoveNext() )
         Console.WriteLine( "The first element is {0}.", myEnumerator.Current );

   }

}

/*
This code produces the following output.

red
orange
yellow
green
blue
indigo
violet

The first element is red.

*/

[C++] 
#using <mscorlib.dll>
#using <System.dll>

using namespace System;
using namespace System::Collections::Specialized;

int main() {

   // Creates and initializes a StringCollection.
   StringCollection* myCol = new StringCollection();
   String* myArr[] = { S"red", S"orange", S"yellow", S"green", S"blue", S"indigo", S"violet" };
   myCol->AddRange(myArr);

   // Enumerates the elements in the StringCollection.
   StringEnumerator* myEnumerator = myCol->GetEnumerator();
   while (myEnumerator->MoveNext())
      Console::WriteLine(S"{0}", myEnumerator->Current);
   Console::WriteLine();

   // Resets the enumerator and displays the first element again.
   myEnumerator->Reset();
   if (myEnumerator->MoveNext())
      Console::WriteLine(S"The first element is {0}.", myEnumerator->Current);

}


/*
This code produces the following output.

red
orange
yellow
green
blue
indigo
violet

The first element is red.

*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.Collections.Specialized

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

Assembly: System (in System.dll)

See Also

StringEnumerator Members | System.Collections.Specialized Namespace | IEnumerable | IEnumerator | StringCollection

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