Attribute.Match(Object) 方法

定義

在衍生類別中覆寫時,會傳回值,表示這個執行個體是否等於指定物件。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

參數

obj
Object

Object 的這個執行個體相互比較的 AttributeAn Object to compare with this instance of Attribute.

傳回

如果這個執行個體等於 obj,則為 true,否則為 falsetrue if this instance equals obj; otherwise, false.

備註

這個方法會判斷其中一個 Attribute 是否等於另一個。This method determines if one Attribute equals another. 其預設的實作為 Equals,它會判斷兩個屬性是否屬於相同的型別,並具有相同的域值。Its default implementation is the same as Equals, which determines whether two attributes are of the same type and have the same field values.

一般來說,Equals 方法是用來執行參考或值相等的標準測試。In general, the Equals method is intended to perform a standard test for reference or value equality. 當您想要針對以其他條件(而不是這兩個屬性實例都屬於相同類型且具有相同的值)的相等性執行自訂比較時,可以覆寫 Match 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,您可以覆寫 Match 方法,以比較下列案例中的屬性:For example, you can override the Match method to compare attributes in the following scenarios:

  • 屬性包含位欄位,而且如果已設定特定位,則會將兩個屬性實例視為相等。An attribute includes a bit field, and you consider two attribute instances equal if a particular bit is set. 例如,NumericDisplay 屬性可能會包含一個位欄位,指出用戶端支援的數值格式(例如二進位、八進位、十進位和十六進位)。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. 如果兩個實例支援相同的數值格式,則覆寫的 Match 方法可能會將其視為相等。The overridden Match method might consider two instances equal if they support the same numeric format.

  • 屬性包含多個欄位,其中包含相同類型的資訊,或包含值可以任意順序的陣列。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 屬性可能包含作者名稱的多個欄位。For example, an Author attribute might include multiple fields for author names. 如果覆寫的 Match 方法有相同的作者,不論每個欄位是否等於對應的欄位,都可以將兩個實例視為相等。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.

範例Example

下列範例說明如何使用 Match 來建立屬性值的自訂比較方法。The following example illustrates the use of Match to create a custom comparison method for attribute values. 如果定義 AuthorsAttribute,內部包含儲存作者名稱的 List<String>If defines an AuthorsAttribute that internally contains a List<String> that stores authors' names. 因為名稱可以依任何順序出現在清單中,所以它會覆寫 Match 方法來比較作者名稱,而不論其在清單中的位置為何。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. 請注意,Equals 方法(可執行值相等的測試)會從 Match 方法傳回不同的結果。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

適用於