Attribute.Match(Object) Méthode

Définition

En cas de substitution dans une classe dérivée, retourne une valeur indiquant si cette instance équivaut à un objet spécifié.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

Paramètres

obj
Object

Object à comparer à cette instance de Attribute.An Object to compare with this instance of Attribute.

Retours

true si cette instance équivaut à obj ; sinon, false.true if this instance equals obj; otherwise, false.

Remarques

Cette méthode détermine si une Attribute est égale à une autre.This method determines if one Attribute equals another. Son implémentation par défaut est identique à Equals, qui détermine si deux attributs sont du même type et ont les mêmes valeurs de champ.Its default implementation is the same as Equals, which determines whether two attributes are of the same type and have the same field values.

En général, la méthode Equals est destinée à effectuer un test standard pour l’égalité des références ou des valeurs.In general, the Equals method is intended to perform a standard test for reference or value equality. Vous pouvez substituer la méthode Match lorsque vous souhaitez effectuer une comparaison personnalisée d’égalité basée sur certains critères autres que ceux qui sont du même type et qui ont des valeurs identiques.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 identical values. Par exemple, vous pouvez substituer la méthode Match pour comparer des attributs dans les scénarios suivants :For example, you can override the Match method to compare attributes in the following scenarios:

  • Un attribut comprend un champ de bits, et vous pensez que deux instances d’attribut sont égales si un bit particulier est défini.An attribute includes a bit field, and you consider two attribute instances equal if a particular bit is set. Par exemple, un attribut NumericDisplay peut inclure un champ de bits qui indique les formats numériques (tels que binaire, octal, décimal et hexadécimal) pris en charge par un client.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. La méthode Match substituée peut considérer deux instances comme étant égales si elles prennent en charge le même format numérique.The overridden Match method might consider two instances equal if they support the same numeric format.

  • Un attribut inclut plusieurs champs qui contiennent le même type d’informations, ou il contient un tableau dans lequel les valeurs peuvent être dans n’importe quel ordre.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. Par exemple, un attribut Author peut inclure plusieurs champs pour les noms d’auteur.For example, an Author attribute might include multiple fields for author names. La méthode Match substituée peut considérer deux instances comme égales si elles ont les mêmes auteurs, même si chaque champ est égal au champ correspondant.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.

ExempleExample

L’exemple suivant illustre l’utilisation de Match pour créer une méthode de comparaison personnalisée pour les valeurs d’attribut.The following example illustrates the use of Match to create a custom comparison method for attribute values. Si définit un AuthorsAttribute qui contient en interne un List<String> qui stocke les noms des auteurs.If defines an AuthorsAttribute that internally contains a List<String> that stores authors' names. Étant donné que les noms peuvent se produire dans n’importe quel ordre dans la liste, il remplace la méthode Match pour comparer les noms des auteurs, quel que soit leur emplacement dans la liste.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. Notez que la méthode Equals, qui effectue un test pour l’égalité des valeurs, retourne des résultats différents de la méthode Match.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

S’applique à