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是否相等。This method determines if one Attribute equals another. 其默认实现与相同Equals, 它确定两个特性是否属于同一类型并且具有相同的字段值。Its default implementation is the same as Equals, which determines whether two attributes are of the same type and have the same field values.

通常, 此Equals方法用于执行引用或值相等性的标准测试。In general, the Equals method is intended to perform a standard test for reference or value equality. 如果要针对相等Match性执行基于某些条件的相等性比较, 而不是这两个属性实例属于同一类型并且具有相同的值, 则可以重写方法。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, 你可以在以下情况Match下重写方法来比较特性:For example, you can override the Match method to compare attributes in the following scenarios:

  • 如果设置了某个特定的位, 则属性包含位域, 并将两个属性实例视为相等。An attribute includes a bit field, and you consider two attribute instances equal if a particular bit is set. 例如, NumericDisplay属性可能包含一个位域, 指示客户端支持的数字格式 (如 binary、八进制、十进制和十六进制)。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. 如果重Match写的方法支持同一数字格式, 则可能会将两个实例视为相等。The overridden Match method might consider two instances equal if they support the same numeric format.

  • 属性包含多个字段, 这些字段包含相同类型的信息, 或包含一个可按任意顺序进行值的数组。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, 一个Author属性可能包含多个用于作者姓名的字段。For example, an Author attribute might include multiple fields for author names. 如果两Match个实例具有相同的作者, 而不考虑每个字段是否等于对应的字段, 则该重写的方法可能会将两个实例视为相等。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Match如何使用来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. 如果定义一个AuthorsAttribute , 它在内部List<String>包含存储作者姓名的。If defines an AuthorsAttribute that internally contains a List<String> that stores authors' names. 由于名称可以在列表中以任意顺序出现, 因此它将重Match写方法以比较作者姓名, 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, 用于执行值相等性测试的Match 方法从方法返回不同的结果。EqualsNote 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