Attribute.Match Method

Parameters

• obj
  Type: System.Object
  An Object to compare with this instance of Attribute.

Return Value

Type: System.Boolean
true if this instance equals obj; otherwise, false.

Imports System.Reflection

Module Example

   ' A custom attribute to allow 2 authors per method.
   <AttributeUsage(AttributeTargets.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

      ' Determine if the object is a match to this one.
      Public Overrides Function Match(ByVal obj As Object) As Boolean
         ' Obviously a match.
         If obj Is Me Then
            Return True
         End If

         ' Obviously we're not nothing, so no.
         If obj Is Nothing Then
            Return False
         End If

         If TypeOf obj Is AuthorsAttribute Then
            ' Combine the hash codes and see if they're unchanged.
            Dim authObj As AuthorsAttribute = CType(obj, AuthorsAttribute)
            Dim firstHash As Integer = authObj.GetHashCode() And GetHashCode()
            If firstHash = GetHashCode() Then
               Return True
            Else
               Return False
            End If
         Else
            Return False
         End If
      End Function

   End Class
   Public Class TestClass1
      <Authors("William Shakespeare", "Herman Melville")> _
      Public Sub Method1()
      End Sub

      <Authors("Leo Tolstoy", "John Milton")> _
      Public Sub Method2()
      End Sub
   End Class
   Public Class TestClass2
      <Authors("William Shakespeare", "Herman Melville")> _
      Public Sub Method1()
      End Sub

      <Authors("Leo Tolstoy", "John Milton")> _
      Public Sub Method2()
      End Sub

      <Authors("Francis Bacon", "Miguel Cervantes")> _
      Public Sub Method3()
      End Sub
   End Class

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      ' Get the type for both classes to access their metadata.
      Dim clsType1 As Type = GetType(TestClass1)
      Dim clsType2 As Type = GetType(TestClass2)

      Dim mInfo1 As MethodInfo
      ' Iterate through each method of the first class.
      For Each mInfo1 In clsType1.GetMethods()
         ' Check each method for the Authors attribute.
         Dim attr1 As Attribute = Attribute.GetCustomAttribute(mInfo1, _
             GetType(AuthorsAttribute))
         If Not attr1 Is Nothing And TypeOf attr1 Is AuthorsAttribute Then
            Dim authAttr1 As AuthorsAttribute = _
                CType(attr1, AuthorsAttribute)
            ' Display the authors.
            outputBlock.Text &= String.Format("Method {0} was authored by {1} and {2}.", _
                            mInfo1.Name, authAttr1.AuthorName1, _
                            authAttr1.AuthorName2) & vbCrLf
            Dim mInfo2 As MethodInfo
            ' Iterate through each method of the second class.
            For Each mInfo2 In clsType2.GetMethods()
               ' Check each method for the Authors attribute.
               Dim attr2 As Attribute = Attribute.GetCustomAttribute( _
                   mInfo2, GetType(AuthorsAttribute))
               If Not attr2 Is Nothing And _
                   TypeOf attr2 Is AuthorsAttribute Then
                  Dim authAttr2 As AuthorsAttribute = _
                      CType(attr2, AuthorsAttribute)
                  ' Compare with the authors in the first class.
                  If authAttr2.Match(authAttr1) = True Then
                     outputBlock.Text &= String.Format("Method {0} in class {1} was " + _
                                 "also authored by the same team.", _
                                 mInfo2.Name, clsType2.Name) & vbCrLf
                  End If
               End If
            Next
            outputBlock.Text &= "" & vbCrLf
         End If
      Next
   End Sub
End Module

' Output:
' Method Method1 was authored by William Shakespeare and Herman Melville.
' Method Method1 in class TestClass2 was also authored by the same team.
' 
' Method Method2 was authored by Leo Tolstoy and John Milton.
' Method Method2 in class TestClass2 was also authored by the same team.

using System;
using System.Reflection;

// A custom attribute to allow 2 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();
  }

  // Determine if the object is a match to this one.
  public override bool Match(object obj)
  {
     // Obviously a match.
     if (obj == this)
        return true;

     // Obviously we're not null, so no.
     if (obj == null)
        return false;

     if (obj is AuthorsAttribute)
        // Combine the hash codes and see if they're unchanged.
        return (((AuthorsAttribute)obj).GetHashCode() & GetHashCode())
           == GetHashCode();
     else
        return false;
  }
}

// Add some authors to methods of a class.
public class TestClass1
{
  [Authors("William Shakespeare", "Herman Melville")]
  public void Method1()
  { }

  [Authors("Leo Tolstoy", "John Milton")]
  public void Method2()
  { }
}

// Add authors to a second class's methods.
public class TestClass2
{
  [Authors("William Shakespeare", "Herman Melville")]
  public void Method1()
  { }

  [Authors("Leo Tolstoy", "John Milton")]
  public void Method2()
  { }

  [Authors("William Shakespeare", "John Milton")]
  public void Method3()
  { }
}

class Example
{
  public static void Demo(System.Windows.Controls.TextBlock outputBlock)
  {
     // Get the type for both classes to access their metadata.
     Type clsType1 = typeof(TestClass1);
     Type clsType2 = typeof(TestClass2);

     // Iterate through each method of the first class.
     foreach (MethodInfo mInfo1 in clsType1.GetMethods())
     {
        // Check each method for the Authors attribute.
        AuthorsAttribute authAttr1 = (AuthorsAttribute)
           Attribute.GetCustomAttribute(mInfo1,
           typeof(AuthorsAttribute));
        if (authAttr1 != null)
        {
           // Display the authors.
           outputBlock.Text += String.Format("Method {0} was authored by {1} " +
                          "and {2}.", mInfo1.Name,
                          authAttr1.AuthorName1,
                          authAttr1.AuthorName2) + "\n";
           // Iterate through each method of the second class.
           foreach (MethodInfo mInfo2 in clsType2.GetMethods())
           {
              // Check each method for the Authors attribute.
              AuthorsAttribute authAttr2 = (AuthorsAttribute)
                 Attribute.GetCustomAttribute(mInfo2,
                 typeof(AuthorsAttribute));
              // Compare with the authors in the first class.
              if (authAttr2 != null && authAttr2.Match(authAttr1))
                 outputBlock.Text += String.Format("Method {0} in class {1} " +
                    "was authored by the same team.",
                    mInfo2.Name, clsType2.Name) + "\n";
           }
           outputBlock.Text += "" + "\n";
        }
     }
  }
}

/*
 * Output:
 * Method Method1 was authored by William Shakespeare and Herman Melville.
 * Method Method1 in class TestClass2 was authored by the same team.
 * Method Method2 was authored by Leo Tolstoy and John Milton.
 * Method Method2 in class TestClass2 was authored by the same team.
 */