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Attribute.Match Method

When overridden in a derived class, returns a value indicating whether this instance equals a specified object.

[Visual Basic]
Public Overridable Function Match( _
   ByVal obj As Object _
) As Boolean
[C#]
public virtual bool Match(
 object obj
);
[C++]
public: virtual bool Match(
 Object* obj
);
[JScript]
public function Match(
   obj : Object
) : Boolean;

Parameters

obj
An Object to compare with this instance of Attribute.

Return Value

true if this instance equals obj; otherwise, false.

Remarks

This method determines if one Attribute equals another. Its default implementation is the same as Equals, which performs a value and reference comparison. Override this method to implement support for attribute values, such as flags or bitfields, that consist of components that are meaningful in themselves.For example, consider an attribute whose value is a binary field divided into a bitfield of flags. Two instances of this attribute have one flag in set in common while all the other flags differ. The Equal method cannot determine that the two instances have the same flag set, but the Match method can.

Example

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

[Visual Basic] 
Imports System
Imports System.Reflection

Module DemoModule

    ' 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

    ' Add some authors to methods of a 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

    ' Add authors to a second class's methods.
    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

    Sub Main()
        ' 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.
                Console.WriteLine("Method {0} was authored by {1} and {2}.", _
                                mInfo1.Name, authAttr1.AuthorName1, _
                                authAttr1.AuthorName2)
                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
                            Console.WriteLine("Method {0} in class {1} was " + _
                                        "also authored by the same team.", _
                                        mInfo2.Name, clsType2.Name)
                        End If
                    End If
                Next
                Console.WriteLine("")
            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.

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

namespace MatchCS {
    // 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 DemoClass {
        static void Main(string[] args) {
            // 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.
                    Console.WriteLine("Method {0} was authored by {1} " +
                                        "and {2}.", mInfo1.Name, 
                                        authAttr1.AuthorName1, 
                                        authAttr1.AuthorName2);
                    // 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))
                            Console.WriteLine("Method {0} in class {1} " +
                                "was authored by the same team.",
                                mInfo2.Name, clsType2.Name);
                    }
                    Console.WriteLine("");
                }
            }
        }
    }
}

/*
 * 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.
 */

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

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

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

      // Obviously we're not null, so no.
      if (obj == 0)
         return false;

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

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

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

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

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

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

int main() {
   // 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.
   System::Collections::IEnumerator* myEnum = clsType1->GetMethods()->GetEnumerator();
   while (myEnum->MoveNext())
   {
      MethodInfo* mInfo1 = __try_cast<MethodInfo*>(myEnum->Current);
      // Check each method for the Authors attribute.
      AuthorsAttribute* authAttr1 = dynamic_cast<AuthorsAttribute*>
         (Attribute::GetCustomAttribute(mInfo1, __typeof(AuthorsAttribute)));
      if (authAttr1 != 0) {
         // Display the authors.
         Console::WriteLine(S"Method {0} was authored by {1} and {2}.",
            mInfo1->Name, 
            authAttr1->AuthorName1, 
            authAttr1->AuthorName2);
         // Iterate through each method of the second class.
         System::Collections::IEnumerator* myEnum1 = clsType2->GetMethods()->GetEnumerator();
         while (myEnum1->MoveNext())
         {
            MethodInfo* mInfo2 = __try_cast<MethodInfo*>(myEnum1->Current);
            // Check each method for the Authors attribute.
            AuthorsAttribute* authAttr2 = dynamic_cast<AuthorsAttribute*>(
               Attribute::GetCustomAttribute(mInfo2, __typeof(AuthorsAttribute)));
            // Compare with the authors in the first class.
            if (authAttr2 != 0 && authAttr2->Match(authAttr1))
               Console::WriteLine(S"Method {0} in class {1} was authored by the same team.",
                  mInfo2->Name, clsType2->Name);
         }
         Console::WriteLine();
      }
   }
}

/*
 * 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.
 */

[JScript] 
import System;
import System.Reflection;

package MatchJS {
    // A custom attribute to allow 2 authors per method.
    AttributeUsage(AttributeTargets.Method) public 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( value: String ) {
            authorName1 = value;
        }

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

        // Determine if the object is a match to this one.
        public override function Match(obj) : boolean {
            // Obviously a match.
            if (obj == this)
                return true;
            // Obviously we're not null, so no.
            if (obj == null)
                return false;

            if (obj instanceof 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 function Method1() : void 
        {}

        Authors("Leo Tolstoy", "John Milton")
        public function Method2() : void 
        {}
    }

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

        Authors("Leo Tolstoy", "John Milton")
        public function Method2() : void
        {}

        Authors("William Shakespeare", "John Milton")
        public function Method3() : void 
        {}
    }

    class DemoClass {
        static function Main() : void {
            // Get the type for both classes to access their metadata.
            var clsType1 : Type = TestClass1;
            var clsType2 : Type = TestClass2;

            // Iterate through each method of the first class.
            var methods1 : MethodInfo[] = clsType1.GetMethods();
            for(var i : int in methods1) {
                var mInfo1 : MethodInfo = methods1[i];
                // Check each method for the Authors attribute.
                var authAttr1 : AuthorsAttribute = AuthorsAttribute(
                    Attribute.GetCustomAttribute(mInfo1, AuthorsAttribute));
                if (authAttr1 != null) {
                // Display the authors.
                Console.WriteLine("Method {0} was authored by {1} " +
                                    "and {2}.", mInfo1.Name, 
                                    authAttr1.AuthorName1, 
                                    authAttr1.AuthorName2);
                // Iterate through each method of the second class.
                var methods2 : MethodInfo[] = clsType2.GetMethods()
                for( var j : int in methods2) {
                        var mInfo2 : MethodInfo = methods2[j];
                        // Check each method for the Authors attribute.
                        var authAttr2 : AuthorsAttribute = AuthorsAttribute(
                            Attribute.GetCustomAttribute(mInfo2, 
                            AuthorsAttribute));
                        // Compare with the authors in the first class.
                        if (authAttr2 != null && authAttr2.Match(authAttr1))
                            Console.WriteLine("Method {0} in class {1} " +
                                "was authored by the same team.",
                                mInfo2.Name, clsType2.Name);
                }
                Console.WriteLine("");
                }
            }
        }
    }
}

MatchJS.DemoClass.Main();

/*
 * 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.
 */

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

See Also

Attribute Class | Attribute Members | System Namespace

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