Articolo
11/18/2011

TextElementEnumerator Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Enumerates the text elements of a string.

Inheritance Hierarchy

System.Object
System.Globalization.TextElementEnumerator

Namespace: System.Globalization
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Class TextElementEnumerator _
    Implements IEnumerator

[ComVisibleAttribute(true)]
public class TextElementEnumerator : IEnumerator

The TextElementEnumerator type exposes the following members.

Properties

	Name	Description
	Current	Gets the current text element in the string.
	ElementIndex	Gets the index of the text element that the enumerator is currently positioned over.

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Methods

	Name	Description
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetTextElement	Gets the current text element in the string.
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	MoveNext	Advances the enumerator to the next text element of the string.
	Reset	Sets the enumerator to its initial position, which is before the first text element in the string.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

The .NET Framework defines a text element as a unit of text that is displayed as a single character, that is, a grapheme. A text element can be a base character, a surrogate pair, or a combining character sequence. The Unicode Standard defines a surrogate pair as a coded character representation for a single abstract character that consists of a sequence of two code units, where the first unit of the pair is a high surrogate and the second is a low surrogate. The Unicode Standard defines a combining character sequence as a combination of a base character and one or more combining characters. A surrogate pair can represent a base character or a combining character. For more information on surrogate pairs and combining character sequences, see The Unicode Standard at http://www.unicode.org.

Text element enumerators are intended to be used only to read data in the string. Enumerators cannot be used to modify the underlying string.

The enumerator does not have exclusive access to the string.

When an enumerator is created, it takes a snapshot of the current state of the string. If changes are made to the string, such as adding, modifying, or deleting text elements, the snapshot gets out of sync and the enumerator throws an InvalidOperationException. Two enumerators created from the same string at the same time can have different snapshots of the string.

The enumerator is in an invalid state if it is positioned before the first text element in the string or after the last text element in the string. Whenever the enumerator is in an invalid state, calling Current throws an exception.

Initially, the enumerator is positioned before the first text element in the string. Reset also brings the enumerator back to this position. Therefore, after an enumerator is created or after a Reset is called, MoveNext must be called to advance the enumerator to the first text element of the string before reading the value of Current.

Current returns the same object until either MoveNext or Reset is called.

After the end of the string is passed, the enumerator is again in an invalid state and calling MoveNext returns false. Calling Current throws an exception if the last call to MoveNext returned false.

Examples

The following code example shows the values returned by TextElementEnumerator.

Imports System.Globalization

Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      ' Creates and initializes a String containing the following:
      '   - a surrogate pair (high surrogate U+D800 and low surrogate U+DC00)
      '   - a combining character sequence (the Latin small letter "a" followed by the combining grave accent)
      '   - a base character (the ligature "")
      Dim myString As String = ChrW(&HD800) & ChrW(&HDC00) & ChrW(&H61) & ChrW(&H300) & ChrW(&HC6)

      ' Creates and initializes a TextElementEnumerator for myString.
      Dim myTEE As TextElementEnumerator = StringInfo.GetTextElementEnumerator(myString)

      ' Displays the values returned by ElementIndex, Current and GetTextElement.
      ' Current and GetTextElement return a string containing the entire text element. 
      outputBlock.Text &= "Index" + ControlChars.Tab + "Current" + ControlChars.Tab + "GetTextElement" & vbCrLf
      myTEE.Reset()
      While myTEE.MoveNext()
         outputBlock.Text += String.Format("[{0}]:" + ControlChars.Tab + "{1}" + ControlChars.Tab + "{2}", myTEE.ElementIndex, myTEE.Current, myTEE.GetTextElement()) & vbCrLf
      End While

   End Sub 'Main 

End Class 'SamplesTextElementEnumerator

' This example displays the following output.  
' Question marks take the place of high and low surrogates.
'       Index   Current GetTextElement
'       [0]:    ??      ??
'       [2]:    a`      a`
'       [4]:    Æ       Æ

using System;
using System.Globalization;


public class Example
{

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {

      // Creates and initializes a String containing the following:
      //   - a surrogate pair (high surrogate U+D800 and low surrogate U+DC00)
      //   - a combining character sequence (the Latin small letter "a" followed by the combining grave accent)
      //   - a base character (the ligature "")
      String myString = "\uD800\uDC00\u0061\u0300\u00C6";

      // Creates and initializes a TextElementEnumerator for myString.
      TextElementEnumerator myTEE = StringInfo.GetTextElementEnumerator(myString);

      // Displays the values returned by ElementIndex, Current and GetTextElement.
      // Current and GetTextElement return a string containing the entire text element. 
      outputBlock.Text += "Index\tCurrent\tGetTextElement" + "\n";
      myTEE.Reset();
      while (myTEE.MoveNext())
      {
         outputBlock.Text += String.Format("[{0}]:\t{1}\t{2}", myTEE.ElementIndex, myTEE.Current, myTEE.GetTextElement()) + "\n";
      }

   }

}

/*
This code produces the following output.  The question marks take the place of high and low surrogates.

Index   Current GetTextElement
[0]:    ??      ??
[2]:    a`      a`
[4]:    Æ       Æ

*/

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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