AttributeGetHashCode Method
 

Returns the hash code for this instance.

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

Syntax
public override int GetHashCode()
public:
virtual int GetHashCode() override
override GetHashCode : unit -> int
Public Overrides Function GetHashCode As Integer

Return Value

Type:

A 32-bit signed integer hash code.

Examples

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

using System;
using System.Reflection;
using System.Collections.Generic;

// A custom attribute to allow two authors per method.
public class AuthorsAttribute : Attribute 
{
   protected string _authorName1;
   protected string _authorName2;

   public AuthorsAttribute(string name1, string name2) 
   {
      _authorName1 = name1;
      _authorName2 = name2;
   }


   public string AuthorName1 
   {
      get { return _authorName1; }
      set { _authorName1 = value; }
   }

   public string AuthorName2 
   {
      get { return _authorName2; }
      set { _authorName2 = value; }
   }

   // Use the hash code of the string objects and xor them together.
   public override int GetHashCode() 
   {
      return _authorName1.GetHashCode() ^ _authorName2.GetHashCode();
   }
}

// Provide the author names for each method of the class.
public class TestClass 
{
  [Authors("Immanuel Kant", "Lao Tzu")]
  public void Method1()
  {}

  [Authors("Jean-Paul Sartre", "Friedrich Nietzsche")]
  public void Method2()
  {}

  [Authors("Immanuel Kant", "Lao Tzu")]
  public void Method3()
  {}

  [Authors("Jean-Paul Sartre", "Friedrich Nietzsche")]
  public void Method4()
  {}

  [Authors("Immanuel Kant", "Friedrich Nietzsche")]
  public void Method5()
  {}
}

class Example
{
   static void Main() 
   {
      // Get the class type to access its metadata.
      Type clsType = typeof(TestClass);

      // Store author information in a list of tuples.
      var authorsInfo = new List<Tuple<String, AuthorsAttribute>>(); 

      // Iterate through all the methods of the class.
      foreach(var method in clsType.GetMethods()) 
      {
          // Get the Authors attribute for the method if it exists.
          AuthorsAttribute authAttr = 
              (AuthorsAttribute)Attribute.GetCustomAttribute(
              method, typeof(AuthorsAttribute));
          if (authAttr != null) 
             // Add the information to the author list.
             authorsInfo.Add(Tuple.Create(clsType.Name + "." + method.Name,
                                             authAttr));
      }

      // Iterate through the list
      bool[] listed = new bool[authorsInfo.Count]; 
      Console.WriteLine("Method authors:\n");

      for (int ctr = 0; ctr < authorsInfo.Count; ctr++) {
         var authorInfo = authorsInfo[ctr];
         if (!listed[ctr]) {
             Console.WriteLine("{0} and {1}", authorInfo.Item2.AuthorName1,
                                              authorInfo.Item2.AuthorName2);
             listed[ctr] = true;
             Console.WriteLine("   {0}", authorInfo.Item1);
             for (int ctr2 = ctr + 1; ctr2 < authorsInfo.Count; ctr2++) {
                 if (!listed[ctr2]) 
                    if (authorInfo.Item2.Equals(authorsInfo[ctr2].Item2)) {
                       Console.WriteLine("   {0}", authorsInfo[ctr2].Item1);
                       listed[ctr2] = true;  
                    }
            }  
         }   
      }
   }
}
// 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
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
Version Information
Universal Windows Platform
Available since 4.5
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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