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

定义

当在派生类中重写时,返回一个指示此实例是否等于指定对象的值。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

参数

obj
Object Object Object Object

Object 的此实例进行比较的 AttributeAn Object to compare with this instance of Attribute.

返回

如果该实例等于 obj,则为 true;否则,为 falsetrue if this instance equals obj; otherwise, false.

注解

此方法确定一个Attribute等于另一个。This method determines if one Attribute equals another. 其默认实现是相同Equals,用于确定是否两个属性均属于同一类型,具有相同的字段值。Its default implementation is the same as Equals, which determines whether two attributes are of the same type and have the same field values.

一般情况下,Equals方法旨在执行标准测试引用或值是否相等。In general, the Equals method is intended to perform a standard test for reference or value equality. 您可以重写Match方法时您想要执行自定义比较是否相等的基于某些条件不是两个属性实例属于同一类型,并且具有完全相同的值。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. 例如,您可以重写Match方法来比较以下方案中的属性:For example, you can override the Match method to compare attributes in the following scenarios:

  • 属性包含一个位字段,并且考虑两个特性实例等于是否设置了特定的位。An attribute includes a bit field, and you consider two attribute instances equal if a particular bit is set. 例如,NumericDisplay属性可能包括指示哪些数字格式 (例如二进制、 八进制、 十进制和十六进制) 客户端支持的位字段。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. 重写Match方法可能会考虑两个实例相等,是否它们支持相同的数字格式。The overridden Match method might consider two instances equal if they support the same numeric format.

  • 属性包含多个字段包含相同类型的信息,或者它包含的数组中的值可以按任意顺序。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. 例如,Author属性可能包含多个字段,作者姓名。For example, an Author attribute might include multiple fields for author names. 重写Match方法可能会考虑两个实例相等,是否它们具有同一作者不考虑每个字段是否等于对应的字段。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.

示例Example

下面的示例演示如何使用Match创建属性值的自定义比较方法。The following example illustrates the use of Match to create a custom comparison method for attribute values. 如果定义了AuthorsAttribute在内部包含List<String>存储作者的名称。If defines an AuthorsAttribute that internally contains a List<String> that stores authors' names. 名称可以在列表中的任何顺序出现,因为它将替代Match方法来比较作者姓名,而不考虑其在列表中的位置。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. 请注意Equals方法,用于执行测试的值是否相等,返回不同的结果从Match方法。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

适用于