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What's New In VS2008?Extension Metods |   | Did you ever want to have a ToInteger Method on an object of Type String? Did you ever want to add ofther methods to the various types of System.Object? In VS2008, you now can do that with Extension Methods.
Much of what this article discusses came with the advent of LINQ, which you will hear much of in VS2008, However, I will limit this discussion to extending System.Objects. One of the new features in Visual Studio is Extension Methods, which allows you to extend System.Objects, such as Integers, Strings, etc. In this article, I am going to extend several objects.
First, Extension Methods derive from System.Runtime.CompilerServices and so you have to have an Import of that Namespace. Secondly, Extension Methods must appear in a Module in VB.NET. A module is nothing more than a class of Shared Methods, etc. Therefore, the Extension Methods must have an access level of Public. Thirdly, to create an Extension Method, you must use an Extension Attribute as shown in the code snippet below. Finally since I am going to use a Regular Expression I will need to import System.Text.RegularEcpressions.
I will extend the String Object Type by adding several methods to the methods of a String object. Although these are very simple methods, you will get the picture of how you can extend the methods of the System.Object Namespace objects. Now before you decide to replace all of your utility functions by adding too many methods to the String object in the CLR. You might want to think of what that might do to intellisense.
Imports System.Object.Runtime.CompilerServices
Imports System.Text.RegularExpressions
Module Module1
Sub Main()
Class1.TestExtensions()
End Sub
' Extension Methods
<Extension()> _
Public Function IsValidSSN(ByVal ssn As String) As String
Return Regex.IsMatch(ssn, "((\d\d\d-\d\d-\d\d\d\d)|(\d{9}))")
End Function
<Extension()> _
Public Function IsUpper(ByVal s As String) As Boolean
Dim m As Match = Regex.Match(s, "^[A-Z]")
Return m.Success
End Function
<Extension()> _
Public Function IsLower(ByVal s As String) As Boolean
Return Not s.IsUpper
End Function
' This method returns True if the whole string alpha
<Extension()> _
Public Function IsAllAlpha(ByVal s As String) As Boolean
Dim m As Match = Regex.Match(s, "^[A-Za-z]*")
Return s.Length = m.Length
End Function
' Create an ToInteger method on an object of type String
' The desire for this method grew out of the extensive use of Val()
' when I was coding in VB6 and the fact that no such method exists in
' pure VB.NET. This method works similiar to Val() in that it stops
' at the first occurrence of a non-numeric character. It will return a
' value of 0 if the first charachter of the string is not numberic.
<Extension()> _
Public Function ToInteger(ByVal s As String) As Integer
Dim m As Match = Regex.Match(s, "^[0-9]*")
If m Is Nothing OrElse m.Length = 0 Then
Return 0
Else
Return CType(m.Value, Integer)
End If
End Function
<Extension()> _
Public Function EqualsCaseInsensitive(ByVal s1 As String, _
ByVal s2 As String) As Boolean
Return s1.Equals(s2, StringComparison.InvariantCultureIgnoreCase)
End Function
<Extension()> _
Public Shared Function ProperCase(ByVal inputString As String) As String
If inputString.Length > 0 Then
If (inputString.ToUpper.Equals(inputString)) OrElse _
(inputString.ToLower.Equals(inputString)) Then
Dim words() As String = inputString.Split(" ")
For i As Integer = 0 To words.Length - 1
If InStr(words(i), ".") = words(i).Length _
OrElse InStr(words(i), ".") = 0 Then
Dim word() As String = words(i).Split("-")
For j As Integer = 0 To word.Length - 1
If i > 0 Then
If "and_of_a_the".IndexOf(word(j)) > -1 Then
word(j) = word(j).ToLower
Else
word(j) = ProperWord(word(j))
End If
Else
word(j) = ProperWord(word(j))
End If
Next
words(i) = Join(word, "-")
Else
If Len(words(i)) = 2 Then
words(i) = words(i).ToUpper
End If
End If
Next
inputString = Join(words, " ")
End If
End If
Return inputString
End Function
Private Shared Function ProperWord(ByVal word As String) As String
If word.Length > 0 Then
If word = word.ToUpper Or word = word.ToLower Then
word = word.Substring(0, 1).ToUpper & word.Substring(1).ToLower
Else
word = word.Substring(0, 1).ToUpper & word.Substring(1)
End If
If UCase(Left(word, 2)) = "MC" Then
word = "Mc" & Mid(word, 3, 1).ToUpper & Mid(word, 4)
End If
End If
Return word
End Function
End Module
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The following is the code to test the Extension methods that I have added to the String object.
Public Class Class1
Public Shared Sub TestExtensions()
Debug.Print("That A is upper case is " & "A".IsUpper)
Debug.Print("That A is lower case is " & "A".IsLower)
Debug.Print("That A = a ignoring case is " & _
"A".EqualsCaseInsensitive("a"))
Debug.Print("That abc1d is all alpha is " & "abc1d".IsAllAlpha)
Debug.Print("Val of 123a = " & "123a".ToInteger.ToString)
Debug.Print("Valid SSN format = " & "123-46-2134".IsValidSSN)
Debug.Print("Valid SSN format = " & "123456789".IsValidSSN)
Debug.Print("Valid SSN format = " & "12345678".IsValidSSN)
Debug.Print("Valid SSN format = " & "123-23-123".IsValidSSN)
Debug.Print("Proper case of john MCCULLOUGH = " & _
"john mccullough".ProperCase)
End Sub
End Class |
The following are the results, taken from the Output Window, that come from the test of the Extension methods.
That A is upper case is True
That A is lower case is False
That A = a ignoring case is True
That abc1d is all alpha is False
Val of 123a = 123
Valid SSN format = True
Valid SSN format = True
Valid SSN format = False
Valid SSN format = False
Proper case of john MCCULLOUGH = John McCullough
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This should whet your appetite for what you can now do in extending the .NET Framework in VS2008.
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