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Attribute.GetHashCode Method

Returns the hash code for this instance.

[Visual Basic]
Overrides Public Function GetHashCode() As Integer
[C#]
public override int GetHashCode();
[C++]
public: int GetHashCode();
[JScript]
public override function GetHashCode() : int;

Return Value

A 32-bit signed integer hash code.

Example

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

[Visual Basic] 
Imports System
Imports System.Reflection
Imports System.Collections

Module HashCodeVB

    ' Visual Basic requires that the AttributeUsage be specified.
    ' A custom attribute to allow two authors per method.
    <AttributeUsage(AttributeTargets.All.Method)> _
    Public Class AuthorsAttribute
        Inherits Attribute

        Public Sub New(ByVal name1 As String, ByVal name2 As String)
            myAuthorName1 = name1
            myAuthorName2 = name2
        End Sub

        Protected myAuthorName1 As String
        Protected myAuthorName2 As String

        Public Property AuthorName1() As String
            Get
                Return myAuthorName1
            End Get
            Set(ByVal Value As String)
                myAuthorName1 = AuthorName1
            End Set
        End Property

        Public Property AuthorName2() As String
            Get
                Return myAuthorName2
            End Get
            Set(ByVal Value As String)
                myAuthorName2 = AuthorName2
            End Set
        End Property

        ' Use the hash code of the string objects and Xor them together.
        Public Overrides Function GetHashCode() As Integer
            Return myAuthorName1.GetHashCode() Xor myAuthorName2.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

    Sub Main()
        ' Get the class type to access its metadata.
        Dim clsType As Type = GetType(TestClass)
        ' Use a hash table to store the hash codes and methods.
        Dim hTable As Hashtable = New Hashtable()
        Dim mInfo As MethodInfo
        ' Iterate through all the methods of the class.
        For Each mInfo In clsType.GetMethods()
            ' Get the unique hash code for these authors.
            Dim attr As Attribute = Attribute.GetCustomAttribute(mInfo, GetType(AuthorsAttribute))
            If Not attr Is Nothing Then
                Dim authAttr As AuthorsAttribute = CType(attr, _
                    AuthorsAttribute)
                Dim hCode As Integer = authAttr.GetHashCode()
                ' See if it's already been added to the hash table.
                If hTable.Contains(hCode) Then
                    Dim o As Object = hTable(hCode)
                    If TypeOf o Is ArrayList Then
                        ' If so, retrieve the array using the Item syntax.
                        Dim al As ArrayList = CType(o, ArrayList)
                        ' Add the method to the array list.
                        al.Add(mInfo.Name)
                        ' Put the edited array list back into the table.
                        hTable(hCode) = al
                    End If
                ' This is the first occurrence of this hash code.
                Else
                    ' Create a new array list.
                    Dim al As ArrayList = New ArrayList()
                    ' Add the method name as the first entry.
                    al.Add(mInfo.Name)
                    ' Add the new hash code and array list to the table.
                    hTable.Add(hCode, al)
                End If
            End If
        Next

        ' Get the hash table's enumerator and iterate through the table.
        Dim dictEnum As IDictionaryEnumerator = hTable.GetEnumerator
        While dictEnum.MoveNext()
            ' Get the array list for this iteration.
            Dim o As Object = dictEnum.Value
            If TypeOf o Is ArrayList Then
                Dim al As ArrayList = CType(o, ArrayList)
                Dim i As Integer
                ' Access each element of the array.
                for i = 0 to al.Count - 1
                    ' For the first element, retrieve the author names.
                    If i = 0 Then
                        Dim methodName as Object = al(i)
                        ' Get the metadata for the method.
                        Dim mInfo2 As MethodInfo = _
                            clsType.GetMethod(CType(methodName, String))
                        ' Retrieve the Authors attribute again.
                        Dim attr As Attribute = Attribute.GetCustomAttribute( _
                            mInfo2, GetType(AuthorsAttribute))
                        If Not attr Is Nothing And _
                            TypeOf attr Is AuthorsAttribute Then
                            ' Convert the attribute to access its data.
                            Dim authAttr As AuthorsAttribute = _
                                CType(attr, AuthorsAttribute)
                            ' Display the author's names.
                            Console.WriteLine("Authors: {0}, {1}", _
                                authattr.AuthorName1, authattr.AuthorName2)
                        Else
                            Console.WriteLine("The authors could not " + _
                                "be retrieved.")
                        End If
                    End If
                    ' Display each method authored by this team.
                    Console.WriteLine(al(i))
                Next i
                Console.WriteLine("")
            End If
        End While
    End Sub
End Module

[C#] 
using System;
using System.Reflection;
using System.Collections;

namespace HashCodeCS 
{
    // A custom attribute to allow two authors per method.
    public class AuthorsAttribute : Attribute 
    {
        public AuthorsAttribute(string name1, string name2) 
        {
            authorName1 = name1;
            authorName2 = name2;
        }

        protected string authorName1;
        protected string authorName2;
    
        public string AuthorName1 
        {
            get { return authorName1; }
            set { authorName1 = AuthorName1; }
        }

        public string AuthorName2 
        {
            get { return authorName2; }
            set { authorName2 = AuthorName2; }
        }

        // 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 DemoClass 
    {
        static void Main(string[] args) 
        {
            // Get the class type to access its metadata.
            Type clsType = typeof(TestClass);

            // Use a hash table to store the hash codes and methods.
            Hashtable hTable = new Hashtable();

            // Iterate through all the methods of the class.
            foreach(MethodInfo mInfo in clsType.GetMethods()) 
            {
                // Get the Authors attribute for the method if it exists.
                AuthorsAttribute authAttr = 
                    (AuthorsAttribute)Attribute.GetCustomAttribute(
                    mInfo, typeof(AuthorsAttribute));
                if (authAttr != null) 
                {
                    // Get the unique hash code for these authors.
                    int hCode = authAttr.GetHashCode();

                    // See if it's already been added to the hash table.
                    if (hTable.Contains(hCode)) 
                    {
                        // If so, retrieve the array using the Item syntax.
                        ArrayList al = (ArrayList)hTable[hCode];
                        // Add the method to the array list.
                        al.Add(mInfo.Name);
                        // Put the edited array list back into the table.
                        hTable[hCode] = al;
                    }

                        // This is the first occurrence of this hash code.
                    else 
                    {
                        // Create a new array list.
                        ArrayList al = new ArrayList();
                        // Add the method name as the first entry.
                        al.Add(mInfo.Name);
                        // Add the new hash code and array list to the table.
                        hTable.Add(hCode, al);
                    }
                }
            }

            // Get the hash table's enumerator and iterate through the table.
            IDictionaryEnumerator dictEnum = hTable.GetEnumerator();
            while (dictEnum.MoveNext()) 
            {
                // Get the array list for this iteration.
                ArrayList al = (ArrayList)dictEnum.Value;
                // Access each element of the array.
                for (int i=0; i<al.Count; i++) 
                {
                    // For the first element, retrieve the author names.
                    if (i == 0) 
                    {
                        // Get the metadata for the method.
                        MethodInfo mInfo = clsType.GetMethod((String)al[i]);
                        // Retrieve the Authors attribute again.
                        AuthorsAttribute authAttr = 
                            (AuthorsAttribute)Attribute.GetCustomAttribute(
                            mInfo, typeof(AuthorsAttribute));
                        // Display the authors names.
                        if (authAttr != null)
                            Console.WriteLine("Authors: {0}, {1}", 
                                authAttr.AuthorName1, authAttr.AuthorName2);
                        else
                            Console.WriteLine("The authors could not be retrieved.");
                    }
                    // Display each method authored by this team.
                    Console.WriteLine(al[i]);
                }
                Console.WriteLine("");
            }
        }
    }
}


[C++] 
#using <mscorlib.dll>
using namespace System;
using namespace System::Reflection;
using namespace System::Collections;

// A custom attribute to allow two authors per method.
public __gc class AuthorsAttribute : public Attribute 
{
public:
   AuthorsAttribute(String* name1, String* name2) 
   {
      authorName1 = name1;
      authorName2 = name2;
   }

protected:
   String* authorName1;
   String* authorName2;

public:
   __property String* get_AuthorName1() { return authorName1; }
   __property void set_AuthorName1( String* value ) { authorName1 = value; }

   __property String* get_AuthorName2() { return authorName2; }
   __property void set_AuthorName2( String* value ) { authorName2 = value; }

   // Use the hash code of the string objects and xor them together.
   int GetHashCode() 
   {
      return authorName1->GetHashCode() ^ authorName2->GetHashCode();
   }
};

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

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

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

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

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

int main() 
{
   // Get the class type to access its metadata.
   Type* clsType = __typeof(TestClass);

   // Use a hash table to store the hash codes and methods.
   Hashtable* hTable = new Hashtable();

   // Iterate through all the methods of the class.
   IEnumerator* myEnum = clsType->GetMethods()->GetEnumerator();
   while (myEnum->MoveNext())
   {
      MethodInfo* mInfo = __try_cast<MethodInfo*>(myEnum->Current);
      // Get the Authors attribute for the method if it exists.
      AuthorsAttribute* authAttr = dynamic_cast<AuthorsAttribute*>
         (Attribute::GetCustomAttribute(mInfo, __typeof(AuthorsAttribute)));
      if (authAttr != 0) 
      {
         // Get the unique hash code for these authors.
         int hCode = authAttr->GetHashCode();

         // See if it's already been added to the hash table.
         if (hTable->Contains(__box(hCode))) 
         {
            // If so, retrieve the array using the Item syntax.
            ArrayList* al = dynamic_cast<ArrayList*>(hTable->Item[__box(hCode)]);
            // Add the method to the array list.
            al->Add(mInfo->Name);
            // Put the edited array list back into the table.
            hTable->Item[__box(hCode)] = al;
         }

         // This is the first occurrence of this hash code.
         else 
         {
            // Create a new array list.
            ArrayList* al = new ArrayList();
            // Add the method name as the first entry.
            al->Add(mInfo->Name);
            // Add the new hash code and array list to the table.
            hTable->Add(__box(hCode), al);
         }
      }
   }

   // Get the hash table's enumerator and iterate through the table.
   IDictionaryEnumerator* dictEnum = hTable->GetEnumerator();
   while (dictEnum->MoveNext()) 
   {
      // Get the array list for this iteration.
      ArrayList* al = dynamic_cast<ArrayList*>(dictEnum->Value);
      // Access each element of the array.
      for (int i=0; i<al->Count; i++) 
      {
         // For the first element, retrieve the author names.
         if (i == 0) 
         {
            // Get the metadata for the method.
            MethodInfo* mInfo = clsType->GetMethod(dynamic_cast<String*>(al->Item[i]));
            // Retrieve the Authors attribute again.
            AuthorsAttribute* authAttr = dynamic_cast<AuthorsAttribute*>
               (Attribute::GetCustomAttribute(mInfo, __typeof(AuthorsAttribute)));
            // Display the authors names.
            if (authAttr != 0)
               Console::WriteLine(S"Authors: {0}, {1}", 
               authAttr->AuthorName1, authAttr->AuthorName2);
            else
               Console::WriteLine(S"The authors could not be retrieved.");
         }
         // Display each method authored by this team.
         Console::WriteLine(al->Item[i]);
      }
      Console::WriteLine(S"");
   }
}

[JScript] 
import System;
import System.Reflection;
import System.Collections;

package HashCodeJS {
    // A custom attribute to allow 2 authors per method.
    public AttributeUsage(AttributeTargets.Method) class AuthorsAttribute extends Attribute {
        public function AuthorsAttribute(name1 : String, name2 : String) {
            authorName1 = name1;
            authorName2 = name2;
        }

        protected var authorName1 : String;
        protected var authorName2 : String;
    
        public function get AuthorName1() : String {
            return authorName1; 
                }

                public function set AuthorName1(AuthorName1 : String) {
            authorName1 = AuthorName1; 
                }

        public function get AuthorName2() : String{
            return authorName2; 
                }

                public function set AuthorName2(AuthorName2 : String) {
            authorName2 = AuthorName2; 
        }

        // Use the hash code of the string objects and xor them together.
        public override function GetHashCode() : int {
            return authorName1.GetHashCode() ^ authorName2.GetHashCode();
        }
    }

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

        public AuthorsAttribute("Jean-Paul Sartre", "Friedrich Nietzche")
        function Method2()
        {}

        public AuthorsAttribute("Immanuel Kant", "Lao Tzu")
        function Method3()
        {}

        public AuthorsAttribute("Jean-Paul Sartre", "Friedrich Nietzche")
        function Method4()
        {}

        public AuthorsAttribute("Immanuel Kant", "Friedrich Nietzche")
        function Method5()
        {}
    }

    class DemoClass {
        static function Main() {
            // Get the class type to access its metadata.
                        var testclass : TestClass = new TestClass();
            var clsType : Type = testclass.GetType();

            // Use a hash table to store the hash codes and methods.
            var hTable : Hashtable = new Hashtable();

            // Iterate through all the methods of the class.
                        var mInfo : MethodInfo[] = clsType.GetMethods()
            for (var i : int = 0; i < mInfo.length; i++) {
                // Get the Authors attribute for the method if it exists.
                var attr : Attribute = Attribute.GetCustomAttribute(mInfo[i], AuthorsAttribute);
                if (attr != null) {
                    // Get the unique hash code for these authors.
                    var hCode : int = attr.GetHashCode();

                    // See if it's already been added to the hash table.
                    if (hTable.Contains(hCode)) {
                        // If so, retrieve the array import the Item syntax.
                        var al : ArrayList = ArrayList(hTable[hCode]);
                        // Add the method to the array list.
                        al.Add(mInfo[i].Name);
                        // Put the edited array list back into the table.
                        hTable[hCode] = al;
                    }

                    // This is the first occurrence of this hash code.
                    else {
                        // Create a new array list.
                        var al2 : ArrayList = new ArrayList();
                        // Add the method name as the first entry.
                        al2.Add(mInfo[i].Name);
                        // Add the new hash code and array list to the table.
                        hTable.Add(hCode, al2);
                    }
                }
            }

            // Get the hash table's enumerator and iterate through the table.
            var dictEnum : IDictionaryEnumerator = hTable.GetEnumerator();
            while (dictEnum.MoveNext()) {
                // Get the array list for this iteration.
                var al3 : ArrayList = ArrayList(dictEnum.Value);
                // Access each element of the array.
                for (var j : int = 0; j < al3.Count; j++) {
                    // For the first element, retrieve the author names.
                    if (j == 0) {
                        // Get the metadata for the method.
                        var mInfo2 : MethodInfo = clsType.GetMethod(String(al3[j]));
                        // Retrieve the Authors attribute again.
                        var attr2 : Attribute = 
                                                      Attribute.GetCustomAttribute(mInfo2, 
                                                                                   AuthorsAttribute);
                        // Display the authors names.
                        if (attr2 != null)
                            Console.WriteLine("Authors: {0}, {1}", 
                                AuthorsAttribute(attr2).AuthorName1, 
                                                                AuthorsAttribute(attr2).AuthorName2);
                        else
                            Console.WriteLine("The authors could not be retrieved.");
                    }
                    // Display each method authored by this team.
                    Console.WriteLine(al3[j]);
                }
                Console.WriteLine("");
            }
        }
    }
}

/*
 *  Output:
 * Authors: Jean-Paul Sartre, Friedrich Nietzche
 * Method4
 * Method2
 * 
 * Authors: Immanuel Kant, Lao Tzu
 * Method3
 * Method1
 *
 * Authors: Immanuel Kant, Friedrich Nietzche
 * Method5
 */

HashCodeJS.DemoClass.Main();

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

Attribute Class | Attribute Members | System Namespace

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