Articolo
11/18/2011

Regex.Replace Method (String, MatchEvaluator)

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

Within a specified input string, replaces all strings that match a specified regular expression with a string returned by a MatchEvaluator delegate.

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

Syntax

'Declaration
Public Function Replace ( _
    input As String, _
    evaluator As MatchEvaluator _
) As String

public string Replace(
    string input,
    MatchEvaluator evaluator
)

Parameters

input
Type: System.String
The string to search for a match.

evaluator
Type: System.Text.RegularExpressions.MatchEvaluator
A custom method that examines each match and returns either the original matched string or a replacement string.

Return Value

Type: System.String
A new string that is identical to the input string, except that a replacement string takes the place of each matched string.

Exceptions

Exception	Condition
ArgumentNullException	input is nulla null reference (Nothing in Visual Basic). -or- evaluator is nulla null reference (Nothing in Visual Basic).

ArgumentNullException

input is nulla null reference (Nothing in Visual Basic).

-or-

evaluator is nulla null reference (Nothing in Visual Basic).

Remarks

The Replace(String, MatchEvaluator) method is useful for replacing a regular expression match if any of the following conditions is true:

The replacement string cannot readily be specified by a regular expression replacement pattern.
The replacement string results from some processing done on the matched string.
The replacement string results from conditional processing.

The method is equivalent to calling the Matches(String) method and passing each Match object in the returned MatchCollection collection to the evaluator delegate.

The regular expression is the pattern defined by the constructor for the current Regex object.

The evaluator parameter is the delegate for a custom method that you define and that examines each match. The custom method must have the following signature to match the MatchEvaluator delegate.

Public Function MatchEvaluatorMethod(ByVal match As Match) As String

public string MatchEvaluatorMethod(Match match)

Your custom method returns a string that replaces the matched input.

Examples

The following code example displays an original string, matches each word in the original string, converts the first character of each match to uppercase, then displays the converted string.

Imports System.Text.RegularExpressions

Module Example
   Function CapText(ByVal m As Match) As String
      ' Get the matched string.
      Dim x As String = m.ToString()
      ' If the first char is lower case...
      If Char.IsLower(x.Chars(0)) Then
         ' Capitalize it.
         Return Char.ToUpper(x.Chars(0)) & x.Substring(1, x.Length - 1)
      End If
      Return x
   End Function

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim text As String = "four score and seven years ago"

      outputBlock.Text &= "text=[" & text & "]" & vbCrLf

      Dim rx As New Regex("\w+")

      Dim result As String = rx.Replace(text, AddressOf Example.CapText)

      outputBlock.Text &= "result=[" & result & "]" & vbCrLf
   End Sub
End Module

using System;
using System.Text.RegularExpressions;

class Example
{
   static string CapText(Match m)
   {
      // Get the matched string.
      string x = m.ToString();
      // If the first char is lower case...
      if (char.IsLower(x[0]))
      {
         // Capitalize it.
         return char.ToUpper(x[0]) + x.Substring(1, x.Length - 1);
      }
      return x;
   }

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string text = "four score and seven years ago";

      outputBlock.Text += "text=[" + text + "]" + "\n";

      Regex rx = new Regex(@"\w+");

      string result = rx.Replace(text, new MatchEvaluator(Example.CapText));

      outputBlock.Text += "result=[" + result + "]" + "\n";
   }
}

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.

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