ConditionalWeakTable<TKey,TValue>.CreateValueCallback Délégué

Définition

Représente une méthode qui crée une valeur, autre qu’une valeur par défaut, à ajouter à un objet ConditionalWeakTable<TKey,TValue> dans le cadre d’une paire clé/valeur.Represents a method that creates a non-default value to add as part of a key/value pair to a ConditionalWeakTable<TKey,TValue> object.

public:  where TKey : class where TValue : classdelegate TValue ConditionalWeakTable<TKey, TValue>::CreateValueCallback(TKey key);
public delegate TValue ConditionalWeakTable<TKey,TValue>.CreateValueCallback(TKey key) where TKey : class where TValue : class;
type ConditionalWeakTable<'Key, 'Value (requires 'Key : null and 'Value : null)>.CreateValueCallback = delegate of 'Key -> 'Value
Public Delegate Function ConditionalWeakTable(Of TKey, TValue).CreateValueCallback(key As TKey) As TValue 

Paramètres de type

TKey
TValue

Paramètres

key

Clé qui appartient à la valeur à créer.The key that belongs to the value to create.

Valeur renvoyée

TValue

Instance d’un type référence qui représente la valeur à associer à la clé spécifiée.An instance of a reference type that represents the value to attach to the specified key.

Héritage
ConditionalWeakTable<TKey,TValue>.CreateValueCallback

Exemples

L’exemple suivant définit une MainClass classe et une MainInfo classe.The following example defines a MainClass class and a MainInfo class. MainInfofournit des informations sur MainClass l’instance.MainInfo provides information about the MainClass instance. Il définit également une méthode statiqueShared (en Visual Basic CreateAttachedValue ) qui ConditionalWeakTable<TKey,TValue>.CreateValueCallback peut être assignée au délégué et passée à GetValue la méthode.It also defines a static (Shared in Visual Basic) CreateAttachedValue method that can be assigned to the ConditionalWeakTable<TKey,TValue>.CreateValueCallback delegate and passed to the GetValue method. L’exemple appelle la GetValue méthode pour ajouter un MainClass objet et son objet MainInfo correspondant à une ConditionalWeakTable<TKey,TValue> table.The example calls the GetValue method to add a MainClass object and its corresponding MainInfo object to a ConditionalWeakTable<TKey,TValue> table. L’exemple illustre également des appels aux Add méthodes et GetOrCreateValue pour ajouter des paires clé/valeur à la table, et un appel à la TryGetValue méthode pour récupérer la valeur qui appartient à une clé existante.The example also illustrates calls to the Add and GetOrCreateValue methods to add key/value pairs to the table, and a call to the TryGetValue method to retrieve the value that belongs to an existing key.

using System;
using System.Reflection;
using System.Runtime.CompilerServices;

public class Example
{
   string Name; 
   
   public Example(string name)
   {
      this.Name = name;
   }
   
   public override string ToString()
   {
      return this.Name;
   }
}

// Define a class to contain information about each Example instance.
public class ExampleInfo
{
   public string Name;
   public int Methods;
   public int Properties;
   
   public override string ToString()
   {
      return String.Format("{0}: {1} Methods, {2} Properties", 
                           this.Name, this.Methods, this.Properties);
   }
}

public class ExampleTest
{
   private static BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;

   public static void Main()
   {
      Example ex1 = new Example("ex1");
      Example ex2 = new Example("ex2");
      Example ex3 = new Example("ex3");
      
      ExampleInfo exInfo1 = new ExampleInfo(); 
      exInfo1.Name = ex1.ToString();
      exInfo1.Methods = ex1.GetType().GetMethods(flags).Length;
      exInfo1.Properties = ex1.GetType().GetProperties(flags).Length;
      
      ExampleInfo exInfo3 = new ExampleInfo(); 
      exInfo3.Name = ex3.ToString();
      exInfo3.Methods = ex3.GetType().GetMethods(flags).Length;
      exInfo3.Properties = ex3.GetType().GetProperties(flags).Length;

      var attached = new ConditionalWeakTable<Example, ExampleInfo>();
      ExampleInfo value = null;

      // Attach a property to ex1 using the Add method, then retrieve it.
      attached.Add(ex1, exInfo1);
      if (attached.TryGetValue(ex1, out value))
         Console.WriteLine("{0}, {1}", ex1, value);
      else
         Console.WriteLine("{0} does not have an attached property.", ex1);

      // Attempt to retrieve the value attached to ex2.
      value = attached.GetValue(ex2, ExampleTest.CreateAttachedValue);      
      if (attached.TryGetValue(ex2, out value))
         Console.WriteLine("{0}, {1}", ex2, value);
      else 
         Console.WriteLine("{0} does not have an attached property.", ex2);
      
      // Attempt to retrieve the value attached to ex3.
      value = attached.GetOrCreateValue(ex3);
      Console.WriteLine("{0}, {1}", ex3, value);
   }

   public static ExampleInfo CreateAttachedValue(Example ex)
   {
      ExampleInfo info = new ExampleInfo();
      info.Name = ex.ToString();
      info.Methods = ex.GetType().GetMethods(flags).Length;
      info.Properties = ex.GetType().GetProperties(flags).Length;
      return info;
   }
}
// The example displays the following output:
//       ex1, ex1: 4 Methods, 0 Properties
//       ex2, ex2: 4 Methods, 0 Properties
//       ex3, : 0 Methods, 0 Properties
Imports System.Reflection
Imports System.Runtime.CompilerServices

Public Class Example
   Public Name As String
   
   Public Sub New(name As String)
      Me.Name = name
   End Sub
   
   Public Overrides Function ToString() As String
      Return Me.Name
   End Function
End Class

' Define a class to contain information about each Example instance.
Public Class ExampleInfo
   Public Name As String
   Public Methods As Integer
   Public Properties As Integer
   
   Public Overrides Function ToString() As String
      Return String.Format("{0}: {1} Methods, {2} Properties", _
                           Me.Name, Me.Methods, Me.Properties)
   End Function
End Class

Module TestExample

   Private flags As BindingFlags = BindingFlags.Public Or BindingFlags.Instance

   Public Sub Main()
      Dim ex1 As New Example("ex1")
      Dim ex2 As New Example("ex2")
      Dim ex3 As New Example("ex3")
      
      Dim exInfo1 As New ExampleInfo() 
      exInfo1.Name = ex1.ToString()
      exInfo1.Methods = ex1.GetType().GetMethods(flags).Count
      exInfo1.Properties = ex1.GetType().GetProperties(flags).Count
      
      Dim exInfo3 As New ExampleInfo() 
      exInfo3.Name = ex3.ToString()
      exInfo3.Methods = ex3.GetType().GetMethods(flags).Count
      exInfo3.Properties = ex3.GetType().GetProperties(flags).Count

      Dim attached As New ConditionalWeakTable(Of Example, ExampleInfo)
      Dim value As ExampleInfo = Nothing

      ' Attach a property to ex1 using the Add method, then retrieve it.
      attached.Add(ex1, exInfo1)
      If attached.TryGetValue(ex1, value) Then
         Console.WriteLine("{0}, {1}", ex1, value)
      Else
         Console.WriteLine("{0} does not have an attached property.", ex1)
      End If

      ' Attempt to retrieve the value attached to ex2.
      value = attached.GetValue(ex2, AddressOf TestExample.CreateAttachedValue)      
      If attached.TryGetValue(ex2, value) Then
         Console.WriteLine("{0}, {1}", ex2, value)
      Else 
         Console.WriteLine("{0} does not have an attached property.", ex2)
      End If
      
      ' Atttempt to retrieve the value attached to ex3.
      value = attached.GetOrCreateValue(ex3)
      Console.WriteLine("{0}, {1}", ex3, value)
   End Sub
   
   Public Function CreateAttachedValue(ex As Example) As ExampleInfo
      Dim info As New ExampleInfo()
      info.Name = ex.ToString()
      info.Methods = ex.GetType().GetMethods(flags).Count
      info.Properties = ex.GetType().GetProperties(flags).Count
      Return info
   End Function
End Module
' The example displays the following output:
'       ex1, ex1: 4 Methods, 0 Properties
'       ex2, ex2: 4 Methods, 0 Properties
'       ex3, : 0 Methods, 0 Properties

Remarques

Le ConditionalWeakTable<TKey,TValue>.CreateValueCallback délégué encapsule une méthode de rappel appelée par la ConditionalWeakTable<TKey,TValue>.GetValue méthode lorsque la clé passée à la méthode est introuvable dans l' ConditionalWeakTable<TKey,TValue> objet.The ConditionalWeakTable<TKey,TValue>.CreateValueCallback delegate encapsulates a callback method that is invoked by the ConditionalWeakTable<TKey,TValue>.GetValue method when the key passed to the method is not found in the ConditionalWeakTable<TKey,TValue> object. La GetValue méthode passe à la méthode de rappel la clé qui représente un objet managé auquel une valeur de propriété doit être attachée dynamiquement.The GetValue method passes the callback method the key that represents a managed object to which a property value is to be dynamically attached. La méthode est chargée de retourner la valeur de la propriété à son appelant, qui, à son tour, ajoute la paire clé/valeur à la table.The method is responsible for returning the property value to its caller, which, in turn, adds the key/value pair to the table.

La ConditionalWeakTable<TKey,TValue>.CreateValueCallback méthode est utilisée pour retourner une instance d’un type référence qui peut être attaché à la clé spécifiée.The ConditionalWeakTable<TKey,TValue>.CreateValueCallback method is used to return an instance of a reference type that can be attached to the specified key. Cela permet à l’instance d’être initialisée à l’aide de valeurs autres que celles par défaut.It enables that instance to be initialized using non-default values. Si la clé est introuvable dans la table, ConditionalWeakTable<TKey,TValue>.GetOrCreateValue la méthode ajoute une paire clé/valeur dans laquelle la valeur est initialisée à l’aide des valeurs par défaut.If the key is not found in the table, the ConditionalWeakTable<TKey,TValue>.GetOrCreateValue method adds a key/value pair in which the value is initialized using default values.

Méthodes d’extension

GetMethodInfo(Delegate)

Obtient un objet qui représente la méthode représentée par le délégué spécifié.Gets an object that represents the method represented by the specified delegate.

S’applique à

Voir aussi