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Attribute.GetHashCode Method

Returns the hash code for this instance.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Overrides Function GetHashCode As Integer

Return Value

Type: System.Int32
A 32-bit signed integer hash code.

The following code example illustrates the use of GetHashCode in the context of Attribute.

Imports System.Reflection
Imports System.Collections.Generic

' A custom attribute to allow two authors per method.
<AttributeUsage(AttributeTargets.Method)> _
Public Class AuthorsAttribute : Inherits Attribute
   Protected _authorName1 As String 
   Protected _authorName2 As String 

   Public Sub New(name1 As String, name2 As String)
      _authorName1 = name1
      _authorName2 = name2
   End Sub 

   Public Property AuthorName1() As String 
      Get 
          Return _authorName1
      End Get 
      Set
          _authorName1 = AuthorName1
      End Set 
   End Property 

   Public Property AuthorName2() As String 
      Get 
          Return _authorName2
      End Get 
      Set
          _authorName2 = AuthorName2
      End Set 
   End Property 

   Public Overrides Function Equals(obj As Object) As Boolean 
      Dim auth As AuthorsAttribute = TryCast(obj, AuthorsAttribute)
      If auth Is Nothing Then Return False 

      If (_authorName1 = auth._authorName1 And _authorName2 = auth._authorName2) Or
         (_authorName1 = auth._authorName2 And _authorName2 = auth._authorName1)
         Return True 
      Else 
         Return False 
      End If  
   End Function 

   ' Use the hash code of the string objects and Xor them together. 
   Public Overrides Function GetHashCode() As Integer 
      Return _authorName1.GetHashCode() Xor _authorName2.GetHashCode()
   End Function 
End Class 

' Provide the author names for each method of the class. 
Public Class TestClass
   <Authors("Immanuel Kant", "Lao Tzu")> _
   Public Sub Method1()
   End Sub

   <Authors("Jean-Paul Sartre", "Friedrich Nietzsche")> _
   Public Sub Method2()
   End Sub

   <Authors("Immanuel Kant", "Lao Tzu")> _
   Public Sub Method3()
   End Sub

   <Authors("Jean-Paul Sartre", "Friedrich Nietzsche")> _
   Public Sub Method4()
   End Sub

   <Authors("Immanuel Kant", "Friedrich Nietzsche")> _
   Public Sub Method5()
   End Sub 
End Class 

Public Module Example
    Sub Main()
        ' Get the TestClass type to access its metadata. 
        Dim clsType As Type = GetType(TestClass)

        ' Store author information in a list of tuples. 
        Dim authorsInfo As New List(Of Tuple(Of String, AuthorsAttribute)) 
        ' Iterate through all the methods of the class. 
        For Each method In clsType.GetMethods()
            ' Get the authors attribute information  
            Dim authAttr As AuthorsAttribute = CType(Attribute.GetCustomAttribute(method, GetType(AuthorsAttribute)),
                                                     AuthorsAttribute)
            If authAttr IsNot Nothing Then 
                ' Add the information to the author list.
                authorsInfo.Add(Tuple.Create(clsType.Name + "." + method.Name,
                                             authAttr))
            End If 
        Next 

        ' Iterate through the list. 
        Dim listed(authorsInfo.Count - 1) As Boolean 
        Console.WriteLine("Method authors:")
        Console.WriteLine()
        For ctr As Integer = 0 To authorsInfo.Count - 1
           Dim authorInfo = authorsInfo(ctr)
           If Not listed(ctr)
              Console.WriteLine("{0} and {1}", authorInfo.Item2.AuthorName1,
                                               authorInfo.Item2.AuthorName2)
              listed(ctr) = True
              Console.WriteLine("   {0}", authorInfo.Item1)
              For ctr2 As Integer = ctr + 1 To authorsInfo.Count - 1
                 If Not listed(ctr2) 
                    If authorInfo.Item2.Equals(authorsInfo(ctr2).Item2) Then
                       Console.WriteLine("   {0}", authorsInfo(ctr2).Item1)
                       listed(ctr2) = true  
                    End if
                 End If  
              Next   
           End If    
        Next 
    End Sub 
End Module 
' The example displays the following output: 
'       Method Authors: 

'       Immanuel Kant and Lao Tzu 
'          TestClass.Method1 
'          TestClass.Method3 
'       Jean-Paul Sartre and Friedrich Nietzsche 
'          TestClass.Method2 
'          TestClass.Method4 
'       Immanuel Kant and Friedrich Nietzsche 
'          TestClass.Method5

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, 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.

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