Attribute.Match(Object) Attribute.Match(Object) Attribute.Match(Object) Attribute.Match(Object) Method

Definition

Beim Überschreiben in einer abgeleiteten Klasse wird ein Wert zurückgegeben, der angibt, ob diese Instanz einem bestimmten Objekt entspricht. When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.

public:
 virtual bool Match(System::Object ^ obj);
public virtual bool Match (object obj);
abstract member Match : obj -> bool
override this.Match : obj -> bool
Public Overridable Function Match (obj As Object) As Boolean

Parameter

obj
Object Object Object Object

Ein Object, das mit dieser Instanz von Attribute verglichen werden soll. An Object to compare with this instance of Attribute.

Returns

true, wenn diese Instanz obj gleicht; andernfalls false. true if this instance equals obj; otherwise, false.

Remarks

Diese Methode bestimmt, ob eine Attribute gleich einem anderen.This method determines if one Attribute equals another. Die Standardimplementierung ist identisch mit Equals, der bestimmt, ob die beiden Attribute vom gleichen Typ sind und die Feldwerten haben.Its default implementation is the same as Equals, which determines whether two attributes are of the same type and have the same field values.

Im Allgemeinen die Equals Methode soll einen standard-Test für Verweis- oder Werttyp auf Gleichheit durchzuführen.In general, the Equals method is intended to perform a standard test for reference or value equality. Sie können außer Kraft setzen der Match Methode, wenn Sie einen benutzerdefinierten Vergleich Gleichheit durchzuführen, die basiert auf den Kriterien nicht, dass zwei Instanzen Attribut möchten den gleichen Typ aufweisen und Identifical-Werte aufweisen.You can override the Match method when you want to perform a custom comparison for equality that is based on some criteria other than that two attribute instances are of the same type and have identifical values. Sie können z. B. überschreiben die Match Methode, um Attribute in den folgenden Szenarien zu vergleichen:For example, you can override the Match method to compare attributes in the following scenarios:

  • Ein Attribut enthält ein Bitfeld, und Sie in Betracht ziehen, dass zwei Attributinstanzen entsprechen, wenn ein bestimmtes Bit festgelegt ist.An attribute includes a bit field, and you consider two attribute instances equal if a particular bit is set. Z. B. eine NumericDisplay Attribut sind zum Beispiel ein Bitfeld, der angibt, welche numerische Formate (z. B. binäre, oktale, Dezimalstellen und hexadezimal) ein Client unterstützt.For example, a NumericDisplay attribute might include a bit field that indicates what numeric formats (such as binary, octal, decimal, and hexadecimal) a client supports. Die überschriebene Match Methode erwägen, zwei Instanzen gleich, wenn sie das gleiche numerische Format unterstützen.The overridden Match method might consider two instances equal if they support the same numeric format.

  • Ein Attribut enthält mehrere Felder, die die gleiche Art von Informationen enthalten, oder er enthält ein Array, in der Werte in beliebiger Reihenfolge enthalten sein können.An attribute includes multiple fields that contain the same kind of information, or it contains an array in which values can be in any order. Z. B. eine Author Attribut kann mehrere Felder für den Autorennamen enthalten.For example, an Author attribute might include multiple fields for author names. Die überschriebene Match Methode erwägen, zwei Instanzen gleich, wenn sie die gleichen Autoren unabhängig davon, ob jedes Feld gleich dem entsprechenden Feld aufweisen.The overridden Match method might consider two instances equal if they have the same authors regardless of whether each field is equal to the corresponding field.

BeispielExample

Das folgende Beispiel veranschaulicht die Verwendung von Match zum Erstellen einer benutzerdefinierten Vergleichsmethode für Attributwerte.The following example illustrates the use of Match to create a custom comparison method for attribute values. Wenn definiert eine AuthorsAttribute enthält, die intern eine List<String> Namen Autoren speichert.If defines an AuthorsAttribute that internally contains a List<String> that stores authors' names. Da die Namen in beliebiger Reihenfolge in der Liste auftreten können, überschreibt es die Match Methode, um die Autorennamen unabhängig von ihrer Position in der Liste verglichen werden soll.Because the names can occur in any order in the list, it overrides the Match method to compare author names regardless of their position in the list. Beachten Sie die Equals Methode, die Wertgleichheit einen Test ausführt, gibt andere Ergebnisse zurück, die Match Methode.Note the Equals method, which performs a test for value equality, returns different results from the Match method.

using System;
using System.Collections.Generic;
using System.Reflection;

// A custom attribute to allow multiple authors per method.
[AttributeUsage(AttributeTargets.Method)]
public class AuthorsAttribute : Attribute 
{
   protected List<string> _authors;

	public AuthorsAttribute(params string[] names) 
   {
      _authors = new List<string>(names);
	}

   public List<string> Authors 
   {
	   get { return _authors; }
   }

	// Determine if the object is a match to this one.
	public override bool Match(object obj) 
   {
      // Return false if obj is null or not an AuthorsAttribute.
      AuthorsAttribute authors2 = obj as AuthorsAttribute;
      if (authors2 == null) return false;
      
		// Return true if obj and this instance are the same object reference.
      if (Object.ReferenceEquals(this, authors2))
         return true;

      // Return false if obj and this instance have different numbers of authors
      if (_authors.Count != authors2._authors.Count)
         return false;
         
      bool matches = false;
      foreach (var author in _authors) 
      { 
         for (int ctr = 0; ctr < authors2._authors.Count; ctr++)
         {
            if (author == authors2._authors[ctr])
            {
               matches = true;
               break;
            }
            if (ctr == authors2._authors.Count)
            {
               matches = false;
            }
         }
      }
      return matches;
   }

   public override string ToString()
   {
      string retval = "";
      for (int ctr = 0; ctr < _authors.Count; ctr++)
      {
         retval += $"{_authors[ctr]}{(ctr < _authors.Count - 1 ? ", " : String.Empty)}";
      }
      if (retval.Trim().Length == 0)
      {
         return "<unknown>";
      }
      return retval;
   }
}

// Add some authors to methods of a class.
public class TestClass {
	[Authors("Leo Tolstoy", "John Milton")]
	public void Method1()
	{}

	[Authors("Anonymous")]
	public void Method2()
	{}

	[Authors("Leo Tolstoy", "John Milton", "Nathaniel Hawthorne")]
	public void Method3()
	{}

	[Authors("John Milton", "Leo Tolstoy")]
	public void Method4()
	{}
}


class Example 
{
	static void Main() 
   {
		// Get the type for TestClass to access its metadata.
		Type clsType = typeof(TestClass);

		// Iterate through each method of the class.
      AuthorsAttribute authors = null;
		foreach(var method in clsType.GetMethods()) 
      {
			// Check each method for the Authors attribute.
			AuthorsAttribute authAttr = (AuthorsAttribute)  Attribute.GetCustomAttribute(method, 
				                         typeof(AuthorsAttribute));
			if (authAttr != null) 
         {
            // Display the authors.
				Console.WriteLine($"{clsType.Name}.{method.Name} was authored by {authAttr}.");

            // Select Method1's authors as the basis for comparison.
            if (method.Name == "Method1")
            {
				   authors = authAttr;
               Console.WriteLine();
               continue;
            }
         
   			// Compare first authors with the authors of this method.
            if (authors.Match(authAttr))
            {
					Console.WriteLine("TestClass.Method1 was also authored by the same team.");
            }

            // Perform an equality comparison of the two attributes.
            Console.WriteLine($"{authors} {(authors.Equals(authAttr) ? "=" : "<>")} {authAttr}");
            Console.WriteLine();
			}
		}
	}
}
// The example displays the following output:
//       TestClass.Method1 was authored by Leo Tolstoy, John Milton.
//       
//       TestClass.Method2 was authored by Anonymous.
//       Leo Tolstoy, John Milton <> Anonymous
//       
//       TestClass.Method3 was authored by Leo Tolstoy, John Milton, Nathaniel Hawthorne.
//       Leo Tolstoy, John Milton <> Leo Tolstoy, John Milton, Nathaniel Hawthorne
//       
//       TestClass.Method4 was authored by John Milton, Leo Tolstoy.
//       TestClass.Method1 was also authored by the same team.
//       Leo Tolstoy, John Milton <> John Milton, Leo Tolstoy

Imports System.Collections.Generic
Imports System.Reflection
                                                               
' A custom attribute to allow multiple authors per method.
<AttributeUsage(AttributeTargets.Method)> _
Public Class AuthorsAttribute : Inherits Attribute 
   Protected _authors As List(Of String)

	Public Sub New(paramarray names As String()) 
      _authors = New List(Of string)(names)
	End Sub

   Public ReadOnly Property Authors As List(Of String) 
	   Get 
         Return _authors
      End Get   
   End Property

	' Determine if the object is a match to this one.
	Public Overrides Function Match(obj As Object) As Boolean 
      ' Return false if obj is null or not an AuthorsAttribute.
      Dim authors2 As AuthorsAttribute = DirectCast(obj, AuthorsAttribute)
      If authors2 Is Nothing Then Return False
      
		' Return true if obj and this instance are the same object reference.
      If Object.ReferenceEquals(Me, authors2) Then Return True

      ' Return false if obj and this instance have different numbers of authors
      If _authors.Count <> authors2._authors.Count Then Return False
         
      Dim matches As Boolean = False
      For Each author in _authors 
         For ctr As Integer = 0 To authors2._authors.Count - 1
            If author = authors2._authors(ctr) Then
               matches = True
               Exit For
            End If
            If ctr = authors2._authors.Count Then matches = False
         Next
      Next
      Return matches
   End Function

   Public Overrides Function ToString() As String
      Dim retval As String = ""
      For ctr As Integer = 0 To _authors.Count -1
         retval += $"{_authors(ctr)}{If(ctr < _authors.Count - 1, ", ", String.Empty)}"
      Next
      If retval.Trim().Length = 0 Then Return "<unknown>"

      Return retval
   End Function
End Class

' Add some authors to methods of a class.
Public Class TestClass 
	<Authors("Leo Tolstoy", "John Milton")>
	Public sub Method1()
	End sub

	<Authors("Anonymous")>
	Public Sub Method2()
	End Sub

	<Authors("Leo Tolstoy", "John Milton", "Nathaniel Hawthorne")>
	Public Sub Method3()
	End Sub

	<Authors("John Milton", "Leo Tolstoy")>
	Public Sub Method4()
	End Sub
End Class

Public Module Example 
	Public Sub Main() 
		' Get the type for TestClass to access its metadata.
		Dim clsType As Type = GetType(TestClass)

		' Iterate through each method of the class.
      Dim authors As AuthorsAttribute = Nothing
		For Each method In clsType.GetMethods() 
			' Check each method for the Authors attribute.
			Dim authAttr As AuthorsAttribute = DirectCast(Attribute.GetCustomAttribute(method, 
				                         GetType(AuthorsAttribute)), AuthorsAttribute)
			If authAttr IsNot Nothing Then 
            ' Display the authors.
				Console.WriteLine($"{clsType.Name}.{method.Name} was authored by {authAttr}.")

            ' Select Method1's authors as the basis for comparison.
            If method.Name = "Method1" Then
				   authors = authAttr
               Console.WriteLine()
               Continue For
            End If
         
   			' Compare first authors with the authors of this method.
            If authors.Match(authAttr) Then
					Console.WriteLine("TestClass.Method1 was also authored by the same team.")
            End If

            ' Perform an equality comparison of the two attributes.
            Console.WriteLine($"{authors} {If(authors.Equals(authAttr), "=", "<>")} {authAttr}")
            Console.WriteLine()
			End If
      Next
   End Sub
End Module
' The example displays the following output:
//       TestClass.Method1 was authored by Leo Tolstoy, John Milton.
//       
//       TestClass.Method2 was authored by Anonymous.
//       Leo Tolstoy, John Milton <> Anonymous
//       
//       TestClass.Method3 was authored by Leo Tolstoy, John Milton, Nathaniel Hawthorne.
//       Leo Tolstoy, John Milton <> Leo Tolstoy, John Milton, Nathaniel Hawthorne
//       
//       TestClass.Method4 was authored by John Milton, Leo Tolstoy.
//       TestClass.Method1 was also authored by the same team.
//       Leo Tolstoy, John Milton <> John Milton, Leo Tolstoy

Applies to