MatchEvaluator Delegate

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

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

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

Parameters

match
Type: System.Text.RegularExpressions.Match

The Match object that represents a single regular expression match during a Replace method operation.

Return Value

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

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.

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 Module1
   Public Sub Main()
      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.
      Console.WriteLine(sInput)
      ' Replace matched characters using the delegate method.
      sInput = r.Replace(sInput, myEvaluator)
      ' Write out the modified string.
      Console.WriteLine(sInput)
   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 = i + 1
      Return i.ToString() & i.ToString()
   End Function 
End Module 
' The example displays the following output: 
'       aabbccddeeffcccgghhcccciijjcccckkcc 
'       aabb11ddeeff22cgghh3344iijj5566kk77

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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