Attribute.Match(Object) Methode

Definition

Namespace:

System

Assembly:

System.Runtime.dll

Quelle:

Attribute.cs

Beim Überschreiben in einer abgeleiteten Klasse wird ein Wert zurückgegeben, der angibt, ob diese Instanz einem bestimmten Objekt entspricht.

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

Ein Object, das mit dieser Instanz von Attribute verglichen werden soll.

Gibt zurück

Boolean

true, wenn diese Instanz obj gleicht; andernfalls false.

Hinweise

Mit dieser Methode wird ermittelt, ob eine Attribute gleich der anderen ist. Die Standardimplementierung ist identisch mit Equals, wodurch bestimmt wird, ob zwei Attribute vom gleichen Typ sind und die gleichen Feldwerte aufweisen.

Im Allgemeinen ist die Methode für die Equals Durchführung eines Standardtests auf Verweis- oder Wertgleichheit vorgesehen. Sie können die Match -Methode überschreiben, wenn Sie einen benutzerdefinierten Vergleich für Gleichheit durchführen möchten, der auf einigen anderen Kriterien basiert, als dass zwei Attributinstanzen vom gleichen Typ sind und identische Werte aufweisen. Beispielsweise können Sie die Match -Methode überschreiben, um Attribute in den folgenden Szenarien zu vergleichen:

• Ein Attribut enthält ein Bitfeld, und Sie betrachten zwei Attributinstanzen als gleich, wenn ein bestimmtes Bit festgelegt ist. Ein NumericDisplay Attribut kann beispielsweise ein Bitfeld enthalten, das angibt, welche numerischen Formate (z. B. binär, oktal, dezimal und hexadezimal) ein Client unterstützt. Die überschriebene Match Methode kann zwei Instanzen als gleich betrachten, wenn sie das gleiche numerische Format unterstützen.

• Ein Attribut enthält mehrere Felder, die dieselbe Art von Informationen enthalten, oder es enthält ein Array, in dem Werte in beliebiger Reihenfolge sein können. Ein Author Attribut kann beispielsweise mehrere Felder für Autorennamen enthalten. Die überschriebene Match Methode kann zwei Instanzen als gleich betrachten, wenn sie dieselben Autoren haben, unabhängig davon, ob jedes Feld dem entsprechenden Feld entspricht.

Beispiel

Das folgende Beispiel veranschaulicht die Verwendung von Match zum Erstellen einer benutzerdefinierten Vergleichsmethode für Attributwerte. Wenn ein AuthorsAttribute definiert, das intern ein List<String> enthält, in dem Autorennamen gespeichert werden. Da die Namen in beliebiger Reihenfolge in der Liste auftreten können, wird die Match Methode zum Vergleichen von Autorennamen unabhängig von ihrer Position in der Liste außer Kraft gesetzt. Beachten Sie, dass die Equals Methode, die einen Test auf Wertgleichheit durchführt, andere Ergebnisse als die Match -Methode zurückgibt.

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

open System

// A custom attribute to allow multiple authors per method.
[<AttributeUsage(AttributeTargets.Method); AllowNullLiteral>]
type AuthorsAttribute([<ParamArray>] names: string []) =
    inherit Attribute()

    member val Authors = ResizeArray names

    // Determine if the object is a match to this one.
    override this.Match(obj) =
        match obj with 
        | :? AuthorsAttribute as authors2 ->
            // Return true if obj and this instance are the same object reference.
            if Object.ReferenceEquals(this, authors2) then true
            // Return false if obj and this instance have different numbers of authors
            elif this.Authors.Count <> authors2.Authors.Count then false 
            else
                let authors1 = this.Authors |> set
                let authors2 = this.Authors |> set
                authors1 = authors2
        | _ ->
            // Return false if obj is null or not an AuthorsAttribute.
            false

    override this.ToString() =
        let retval = String.Join(", ", this.Authors)
        if retval.Trim().Length = 0 then 
            "<unknown>" 
        else 
            retval

// Add some authors to methods of a class.
type TestClass() =
    [<Authors("Leo Tolstoy", "John Milton")>]
    member _.Method1() = ()

    [<Authors "Anonymous">]
    member _.Method2() = ()

    [<Authors("Leo Tolstoy", "John Milton", "Nathaniel Hawthorne")>]
    member _.Method3() = ()

    [<Authors("John Milton", "Leo Tolstoy")>]
    member _.Method4() = ()

// Get the type for TestClass to access its metadata.
let clsType = typeof<TestClass>

// Iterate through each method of the class.

let mutable authors = null
for method in clsType.GetMethods() do
    // Check each method for the Authors attribute.
    let authAttr = 
        Attribute.GetCustomAttribute(method, typeof<AuthorsAttribute>)
        :?> AuthorsAttribute

    if authAttr <> null then
        // Display the authors.
        printfn $"{clsType.Name}.{method.Name} was authored by {authAttr}."

        // Select Method1's authors as the basis for comparison.
        if method.Name = "Method1" then
            authors <- authAttr
            printfn ""

        else
            // Compare first authors with the authors of this method.
            if authors.Match authAttr then
                printfn "TestClass.Method1 was also authored by the same team."

            // Perform an equality comparison of the two attributes.
            printfn $"""{authors} {if authors.Equals(authAttr) then "=" else "<>"} {authAttr}"""
            printfn ""

// 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