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MatchEvaluator Delegate

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

Represents the method that is called each time a regular expression match is found during a Replace method operation.

Namespace:  System.Text.RegularExpressions
Assembly:  System (in System.dll)

Syntax

'Declaration
Public Delegate Function MatchEvaluator ( _
    match As Match _
) As String

public delegate string MatchEvaluator(
    Match match
)

Parameters

Return Value

Type: System.String
A string returned by the method that is represented by the MatchEvaluator delegate.

Remarks

You can use a MatchEvaluator delegate method to perform a custom verification or manipulation operation for each match found by a replacement method such as Regex.Replace(String, MatchEvaluator). For each matched string, the Replace method calls the MatchEvaluator delegate method with a Match object that represents the match. The delegate method performs whatever processing you prefer and returns a string that the Replace method substitutes for the matched string.

Examples

The following code example uses the MatchEvaluator delegate to replace every matched group of characters with the number of the match occurrence.

Imports System.Text.RegularExpressions

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim sInput, sRegex As String

      ' The string to search.
      sInput = "aabbccddeeffcccgghhcccciijjcccckkcc"

      ' A very simple regular expression.
      sRegex = "cc"

      Dim r As Regex = New Regex(sRegex)

      ' Assign the replace method to the MatchEvaluator delegate.
      Dim myEvaluator As MatchEvaluator = New MatchEvaluator(AddressOf ReplaceCC)

      ' Write out the original string.
      outputBlock.Text &= sInput & vbCrLf
      ' Replace matched characters using the delegate method.
      sInput = r.Replace(sInput, myEvaluator)
      ' Write out the modified string.
      outputBlock.Text &= sInput & vbCrLf
   End Sub

   Public Function ReplaceCC(ByVal m As Match) As String
      ' Replace each Regex match with the number of the match occurrence.
      Static i As Integer

      i += 1
      Return i.ToString() & i.ToString()
   End Function
End Module
' The example displays the following output:
'       aabbccddeeffcccgghhcccciijjcccckkcc
'       aabb11ddeeff22cgghh3344iijj5566kk77

using System;
using System.Text.RegularExpressions;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string sInput, sRegex;

      // The string to search.
      sInput = "aabbccddeeffcccgghhcccciijjcccckkcc";

      // A very simple regular expression.
      sRegex = "cc";

      Regex r = new Regex(sRegex);

      Example c = new Example();

      // Assign the replace method to the MatchEvaluator delegate.
      MatchEvaluator myEvaluator = new MatchEvaluator(c.ReplaceCC);

      // Write out the original string.
      outputBlock.Text += sInput + "\n";

      // Replace matched characters using the delegate method.
      sInput = r.Replace(sInput, myEvaluator);

      // Write out the modified string.
      outputBlock.Text += sInput + "\n";
   }

   public string ReplaceCC(Match m)
   // Replace each Regex cc match with the number of the occurrence.
   {
      i++;
      return i.ToString() + i.ToString();
   }
   public static int i = 0;
}
// The example displays the following output:
//       aabbccddeeffcccgghhcccciijjcccckkcc
//       aabb11ddeeff22cgghh3344iijj5566kk77

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.