ConditionalWeakTable<TKey,TValue>.CreateValueCallback ConditionalWeakTable<TKey,TValue>.CreateValueCallback ConditionalWeakTable<TKey,TValue>.CreateValueCallback ConditionalWeakTable<TKey,TValue>.CreateValueCallback Delegate

Definizione

Rappresenta un metodo che crea un valore non predefinito da aggiungere come parte di una coppia chiave/valore a un oggetto 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 

Parametri di tipo

TKey
TValue

Parametri

key

Chiave che appartiene al valore da creare.The key that belongs to the value to create.

Valore restituito

TValue

Istanza di un tipo riferimento che rappresenta il valore da associare alla chiave specificata.An instance of a reference type that represents the value to attach to the specified key.

Ereditarietà
ConditionalWeakTable<TKey,TValue>.CreateValueCallbackConditionalWeakTable<TKey,TValue>.CreateValueCallbackConditionalWeakTable<TKey,TValue>.CreateValueCallbackConditionalWeakTable<TKey,TValue>.CreateValueCallback

Esempi

Nell'esempio seguente vengono definite MainClass una classe e MainInfo una classe.The following example defines a MainClass class and a MainInfo class. MainInfofornisce informazioni sull' MainClass istanza di.MainInfo provides information about the MainClass instance. Definisce inoltre un metodo statico (Shared in Visual Basic) CreateAttachedValue che ConditionalWeakTable<TKey,TValue>.CreateValueCallback può essere assegnato al delegato e passato al GetValue metodo.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. Nell'esempio viene chiamato GetValue il metodo per aggiungere MainClass un oggetto e l' MainInfo oggetto corrispondente a ConditionalWeakTable<TKey,TValue> una tabella.The example calls the GetValue method to add a MainClass object and its corresponding MainInfo object to a ConditionalWeakTable<TKey,TValue> table. Nell'esempio vengono inoltre illustrate le chiamate Add ai GetOrCreateValue metodi e per aggiungere coppie chiave/valore alla tabella TryGetValue e una chiamata al metodo per recuperare il valore che appartiene a una chiave esistente.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

Commenti

Il ConditionalWeakTable<TKey,TValue>.CreateValueCallback delegato incapsula un metodo ConditionalWeakTable<TKey,TValue>.GetValue di callback che viene richiamato dal metodo quando la chiave passata al metodo non ConditionalWeakTable<TKey,TValue> viene trovata nell'oggetto.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. Il GetValue metodo passa il metodo di callback alla chiave che rappresenta un oggetto gestito a cui un valore della proprietà deve essere collegato dinamicamente.The GetValue method passes the callback method the key that represents a managed object to which a property value is to be dynamically attached. Il metodo è responsabile della restituzione del valore della proprietà al chiamante, che, a sua volta, aggiunge la coppia chiave/valore alla tabella.The method is responsible for returning the property value to its caller, which, in turn, adds the key/value pair to the table.

Il ConditionalWeakTable<TKey,TValue>.CreateValueCallback metodo viene utilizzato per restituire un'istanza di un tipo di riferimento che può essere allegato alla chiave specificata.The ConditionalWeakTable<TKey,TValue>.CreateValueCallback method is used to return an instance of a reference type that can be attached to the specified key. Consente l'inizializzazione di tale istanza con valori non predefiniti.It enables that instance to be initialized using non-default values. Se la chiave non viene trovata nella tabella, il ConditionalWeakTable<TKey,TValue>.GetOrCreateValue metodo aggiunge una coppia chiave/valore in cui il valore viene inizializzato con i valori predefiniti.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.

Metodi di estensione

GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate)

Ottiene un oggetto che rappresenta il metodo rappresentato dal delegato specificato.Gets an object that represents the method represented by the specified delegate.

Si applica a

Vedi anche