Attribute.Match Method
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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)
Syntax
'Declaration
Public Overridable Function Match ( _
obj As Object _
) As Boolean
public virtual bool Match(
Object obj
)
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.
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 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.
Examples
The following code example illustrates the use of Match in the context of Attribute.
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.
*/
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.