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Attribute.GetHashCode Method

Returns the hash code for this instance.

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

public override int GetHashCode()

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.

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

.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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