ConditionalWeakTable<TKey,TValue>.CreateValueCallback Delegat

Definicja

Reprezentuje metodę, która tworzy wartość różną od wartości domyślnej, która jest dodawana jako część pary klucz/wartość do obiektu ConditionalWeakTable<TKey,TValue>.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 

Parametry typu

TKey
TValue

Parametry

key

Klucz, który należy do wartości, która ma zostać utworzona.The key that belongs to the value to create.

Wartość zwracana

TValue

Wystąpienie typu referencyjnego, które reprezentuje wartość dołączenia do określonego klucza.An instance of a reference type that represents the value to attach to the specified key.

Dziedziczenie
ConditionalWeakTable<TKey,TValue>.CreateValueCallback

Przykłady

W poniższym przykładzie zdefiniowano klasę MainClass i klasę MainInfo.The following example defines a MainClass class and a MainInfo class. MainInfo zawiera informacje na temat wystąpienia MainClass.MainInfo provides information about the MainClass instance. Definiuje także statyczną (Shared w Visual Basic) metodę CreateAttachedValue, którą można przypisać do delegata ConditionalWeakTable<TKey,TValue>.CreateValueCallback i przekazać do metody GetValue.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. Przykład wywołuje metodę GetValue, aby dodać obiekt MainClass i odpowiadający mu obiekt MainInfo do tabeli ConditionalWeakTable<TKey,TValue>.The example calls the GetValue method to add a MainClass object and its corresponding MainInfo object to a ConditionalWeakTable<TKey,TValue> table. Przykład ilustruje także wywołania metod Add i GetOrCreateValue, aby dodać pary klucz/wartość do tabeli i wywołanie metody TryGetValue w celu pobrania wartości należącej do istniejącego klucza.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

Uwagi

Delegat ConditionalWeakTable<TKey,TValue>.CreateValueCallback hermetyzuje metodę wywołania zwrotnego, która jest wywoływana przez metodę ConditionalWeakTable<TKey,TValue>.GetValue, gdy klucz przeszedł do metody nie został znaleziony w obiekcie ConditionalWeakTable<TKey,TValue>.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. Metoda GetValue przekazuje metodę wywołania zwrotnego kluczem, który reprezentuje zarządzany obiekt, do którego ma być dynamicznie dołączona wartość właściwości.The GetValue method passes the callback method the key that represents a managed object to which a property value is to be dynamically attached. Metoda jest odpowiedzialna za zwracanie wartości właściwości do obiektu wywołującego, co z kolei powoduje dodanie pary klucz/wartość do tabeli.The method is responsible for returning the property value to its caller, which, in turn, adds the key/value pair to the table.

Metoda ConditionalWeakTable<TKey,TValue>.CreateValueCallback służy do zwracania wystąpienia typu referencyjnego, który można dołączyć do określonego klucza.The ConditionalWeakTable<TKey,TValue>.CreateValueCallback method is used to return an instance of a reference type that can be attached to the specified key. Umożliwia inicjowanie tego wystąpienia przy użyciu wartości innych niż domyślne.It enables that instance to be initialized using non-default values. Jeśli klucz nie zostanie znaleziony w tabeli, Metoda ConditionalWeakTable<TKey,TValue>.GetOrCreateValue dodaje parę klucz/wartość, w której wartość jest inicjowana przy użyciu wartości domyślnych.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.

Metody rozszerzania

GetMethodInfo(Delegate)

Pobiera obiekt, który reprezentuje metodę reprezentowaną przez określony delegat.Gets an object that represents the method represented by the specified delegate.

Dotyczy

Zobacz też