SortVersion Class

From the .NET Framework 2.0 Service Pack 1 through the .NET Framework 4, each version of the.NET Framework has included tables that contain sort weights and data on string normalization and that are based on a particular version of Unicode. In the .NET Framework 4.5, the presence of these tables depends on the operating system:

• On Windows 7 and previous versions of the Windows operating system, the tables continue to be used for comparing and ordering strings.

• On Windows 8, the .NET Framework delegates string comparison and ordering operations to the operating system.

Consequently, the result of a string comparison can depend not only on the .NET Framework version, but also on the operating system version, as the following table shows.

On Windows 8, because the version of Unicode used in string comparison and ordering depends on the version of the operating system, the results of string comparison may differ even for applications that run on a specific version of the .NET Framework.

The SortVersion class provides information about the Unicode version used by the .NET Framework for string comparison and ordering. It enables developers to write applications that can detect and successfully handle changes in the version of Unicode that is used to compare and sort an application's strings.

You can instantiate a SortVersion object in two ways:

• By calling the SortVersion constructor, which instantiates a new SortVersion object based on a version number and sort ID. This constructor is most useful when recreating a SortVersion object from saved data.

• By retrieving the value of the CompareInfo.Version property. This property provides information about the Unicode version used by the .NET Framework on which the application is running.

The SortVersion class has two properties, FullVersion and SortId, that indicate the Unicode version and the specific culture used for string comparison. The FullVersion property is an arbitrary numeric value that reflects the Unicode version used for string comparison, and the SortId property is an arbitrary Guid that reflects the culture whose conventions are used for string comparison. The values of these two properties are important only when you compare two SortVersion objects by using the Equals method, the Equality operator, or the Inequality operator.

You typically use a SortVersion object when saving or retrieving some form of culture-sensitive, ordered string data, such as indexes or the literal strings themselves. This requires the following steps:

1. When the ordered string data is saved, the FullVersion and SortId property values are also saved.

2. When the ordered string data is retrieved, you can recreate the SortVersion object used for ordering the strings by calling the SortVersion constructor.

3. This newly instantiated SortVersion object is compared with a SortVersion object that reflects the culture whose conventions are used to order the string data.

4. If the two SortVersion objects are not equal, the string data must be reordered.

The example provides an illustration.

The following example contains a portion of the source code from an application that uses the SortVersion class to ensure that the native names of RegionInfo objects are ordered appropriately for the current system and current culture. It uses the BinaryReader and BinaryWriter objects to store and retrieve ordered data from a data file named Regions.dat rather than retrieving and ordering data each time the application is run. The example first checks to determine whether the data file exists. If it does not, it creates the data and sets the reindex flag, which indicates that the data must be resorted and saved again. Otherwise, it retrieves the data and compares the saved SortVersion object with the SortVersion object for the current culture on the current system. If they are not equal, or if the reindex flag had been set previously, it resorts the RegionInfo data.

Imports System.Collections
Imports System.Collections.Generic
Imports System.Globalization
Imports System.IO
Imports System.Text

Public Class Example : Implements IComparer
   Private Const FILENAME As String = ".\Regions.dat" 

   Private Structure Region
      Friend Sub New(id As String, name As String)
         Me.Id = id
         Me.NativeName = name
      End Sub 

      Dim Id As String 
      Dim NativeName As String 

      Public Overrides Function ToString() As String 
         Return Me.NativeName
      End Function 
   End Structure 

   Public Shared Sub Main()
      Dim reindex As Boolean = False 

      Dim regions() As Region
      Dim ver As SortVersion = Nothing 

      ' If the data has not been saved, create it. 
      If Not File.Exists(FILENAME) Then 
         regions = GenerateData()
         ver = CultureInfo.CurrentCulture.CompareInfo.Version  
         reindex = True 
      ' Retrieve the existing data. 
      Else
         regions = RestoreData(ver)
      End If 

      ' Determine whether the current ordering is valid; if not, reorder. 
      If reindex OrElse ver <> CultureInfo.CurrentCulture.CompareInfo.Version Then 
         Array.Sort(regions, New Example())      
         ' Save newly reordered data.
         SaveData(regions)
      End If 

      ' Continue with application... 
   End Sub 

   Private Shared Function GenerateData() As Region()
      Dim regions As New List(Of Region)()

      For Each culture In CultureInfo.GetCultures(CultureTypes.AllCultures)
         If culture.IsNeutralCulture Or culture.Equals(CultureInfo.InvariantCulture) Then Continue For 

         Dim region As New RegionInfo(culture.Name)
         regions.Add(New Region(region.Name, region.NativeName))
      Next 
      Return regions.ToArray()
   End Function 

   Private Shared Function RestoreData(ByRef ver As SortVersion) As Region()
      Dim regions As New List(Of Region)

      Dim rdr As New BinaryReader(File.Open(FILENAME, FileMode.Open))

      Dim sortVer As Integer = rdr.ReadInt32
      Dim sortId As Guid = Guid.Parse(rdr.ReadString())
      ver = New SortVersion(sortVer, sortId)

      Dim id As String, name As String 
      Do While rdr.PeekChar <> -1
         id = rdr.ReadString()
         name = rdr.ReadString()
         regions.Add(New Region(id, name))      
      Loop 
      Return regions.ToArray()
   End Function 

   Private Shared Sub SaveData(regions As Region())
      Dim ver As SortVersion = CultureInfo.CurrentCulture.CompareInfo.Version

      Dim wrtr As New BinaryWriter(File.Open(FILENAME, FileMode.Create))
      wrtr.Write(ver.FullVersion) 
      wrtr.Write(ver.SortId.ToString()) 

      For Each region In regions
         wrtr.Write(region.Id)
         wrtr.Write(region.NativeName)
      Next
      wrtr.Close()
   End Sub 

   Private Function SortByNativeName(o1 As Object, o2 As Object) As Integer _
           Implements IComparer.Compare
        ' Assume that all conversions succeed. 
        Dim r1 As Region = CType(o1, Region)
        Dim r2 As Region = CType(o2, Region)

        Return String.Compare(r1.NativeName, r2.NativeName, 
                              StringComparison.CurrentCulture)         
   End Function 
End Class

.NET Framework

Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference