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Attribute.Match Method

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

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

'Declaration
Public Overridable Function Match ( _
	obj As Object _
) As Boolean

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.

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 bit fields, that consist of components that are meaningful in themselves.

For example, consider an attribute whose value is a binary field divided into a bit field of flags. Two instances of this attribute have one flag in set in common while all the other flags differ. The Equals method cannot determine that the two instances have the same flag set, but the Match method can.

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


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.


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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