WeakReference WeakReference WeakReference WeakReference Class

Définition

Représente une référence faible, qui référence un objet tout en autorisant toujours cet objet à être récupéré lors du garbage collection. Represents a weak reference, which references an object while still allowing that object to be reclaimed by garbage collection.

public ref class WeakReference : System::Runtime::Serialization::ISerializable
[System.Runtime.InteropServices.ComVisible(true)]
[Serializable]
public class WeakReference : System.Runtime.Serialization.ISerializable
type WeakReference = class
    interface ISerializable
Public Class WeakReference
Implements ISerializable
Héritage
WeakReferenceWeakReferenceWeakReferenceWeakReference
Attributs
ComVisibleAttribute SerializableAttribute
Implémente

Exemples

L’exemple suivant montre comment vous pouvez utiliser des références faibles pour maintenir un cache d’objets en tant que ressource pour une application.The following example demonstrates how you can use weak references to maintain a cache of objects as a resource for an application. Le cache est construit à l’aide un IDictionary<TKey,TValue> de WeakReference objets indexé par une valeur d’index.The cache is constructed using an IDictionary<TKey,TValue> of WeakReference objects keyed by an index value. Le Target propriété pour le WeakReference objets est un objet dans un tableau d’octets qui représente les données.The Target property for the WeakReference objects is an object in a byte array that represents data.

L’exemple accède aléatoirement aux objets dans le cache.The example randomly accesses objects in the cache. Si un objet est récupéré pour le garbage collection, un nouvel objet de données est régénéré ; Sinon, l’objet est disponible pour accéder en raison de la référence faible.If an object is reclaimed for garbage collection, a new data object is regenerated; otherwise, the object is available to access because of the weak reference.

using System;
using System.Collections.Generic;

public class Program
{
    public static void Main()
    {
        // Create the cache.
        int cacheSize = 50;
        Random r = new Random();
        Cache c = new Cache(cacheSize);

        string DataName = "";
        GC.Collect(0);
        
        // Randomly access objects in the cache.
        for (int i = 0; i < c.Count; i++) {
            int index = r.Next(c.Count);

            // Access the object by getting a property value.
            DataName = c[index].Name;
        }
        // Show results.
        double regenPercent = c.RegenerationCount/(double)c.Count;
        Console.WriteLine("Cache size: {0}, Regenerated: {1:P2}%", c.Count, regenPercent);
    }
}

public class Cache
{
    // Dictionary to contain the cache.
    static Dictionary<int, WeakReference> _cache;

    // Track the number of times an object is regenerated.
    int regenCount = 0;   

    public Cache(int count)
    {
        _cache = new Dictionary<int, WeakReference>();

        // Add objects with a short weak reference to the cache.
       for (int i = 0; i < count; i++) {
            _cache.Add(i, new WeakReference(new Data(i), false));
        }
    }

    // Number of items in the cache.
    public int Count
    {
        get {  return _cache.Count; }
    }

    // Number of times an object needs to be regenerated.
    public int RegenerationCount
    {
        get { return regenCount; }
    }

    // Retrieve a data object from the cache.
    public Data this[int index]
    {
        get {
            Data d = _cache[index].Target as Data;
            if (d == null) {
                // If the object was reclaimed, generate a new one.
                Console.WriteLine("Regenerate object at {0}: Yes", index);
                d = new Data(index);
                _cache[index].Target = d;
                regenCount++;
            }
            else {
                // Object was obtained with the weak reference.
                Console.WriteLine("Regenerate object at {0}: No", index);
            }

            return d;
       }
    }
}

// This class creates byte arrays to simulate data.
public class Data
{
    private byte[] _data;
    private string _name;

    public Data(int size)
    {
        _data = new byte[size * 1024];
        _name = size.ToString();
    }

    // Simple property.
    public string Name
    {
        get { return _name; }
    }
}
// Example of the last lines of the output:
//
// ...
// Regenerate object at 36: Yes
// Regenerate object at 8: Yes
// Regenerate object at 21: Yes
// Regenerate object at 4: Yes
// Regenerate object at 38: No
// Regenerate object at 7: Yes
// Regenerate object at 2: Yes
// Regenerate object at 43: Yes
// Regenerate object at 38: No
// Cache size: 50, Regenerated: 94%
Imports System.Collections.Generic

Public Class Example
    Public Shared Sub Main()
        ' Create the cache. 
        Dim cacheSize As Integer = 50
        Dim r As Random = New Random()
        Dim c As Cache = New Cache(cacheSize)

        Dim DataName As String = "" 
        GC.Collect(0)
        
        ' Randomly access objects in the cache. 
        For ctr As Integer = 0 To C.Count - 1 
            Dim index As Integer = r.Next(c.Count)

            ' Access the object by getting a property value.
            DataName = c(index).Name
        Next 

        ' Show results. 
        Dim regenPercent As Double = c.RegenerationCount * 100 / c.Count
        Console.WriteLine("Cache size: {0}, Regenerated: {1}%", c.Count, regenPercent)
    End Sub 
End Class 

Public Class Cache
    ' Dictionary to contain the cache. 
    Private Shared _cache As Dictionary(Of Integer, WeakReference)

    ' Track the number of times an object is regenerated. 
    Dim regenCount As Integer = 0

    Public Sub New(ByVal count As Integer)
        _cache = New Dictionary(Of Integer, WeakReference)

        ' Add data objects with a short weak reference to the cache. 
        For ctr = 0 To count - 1
            _cache.Add(ctr, New WeakReference(New Data(ctr)))
        Next
    End Sub 

    ' Number of items in the cache. 
    Public ReadOnly Property Count() As Integer 
        Get 
            Return _cache.Count
        End Get 
    End Property 

    ' Number of times an object needs to be regenerated. 
    Public ReadOnly Property RegenerationCount() As Integer 
        Get 
            Return regenCount
        End Get 
    End Property 

    ' Retrieve a data object from the cache. 
    Default Public ReadOnly Property Item(ByVal index As Integer) As Data
        Get 
            Dim d As Data = TryCast(_cache(index).Target, Data)
            ' If the object was reclaimed, generate a new one.
            If d Is Nothing Then 
                Console.WriteLine("Regenerate object at {0}: Yes", index)
                d = New Data(index)
                _cache(index).Target = d
                regenCount += 1
           Else 
                ' Object was obtained with the weak reference.
                Console.WriteLine("Regenerate object at {0}: No", index.ToString())
            End If 
            Return d
        End Get 
    End Property 
End Class 

' Class that creates byte arrays to simulate data. 
Public Class Data
    Private _data() As Byte 
    Private _name As String 

    Public Sub New(ByVal size As Integer)
        _data = New Byte(((size * 1024)) - 1) {}
        _name = size.ToString
    End Sub 

    ' Simple property for accessing the object. 
    Public ReadOnly Property Name() As String 
        Get 
            Return _name
        End Get 
    End Property 
End Class 
' Example of the last lines of the output: 
' ... 
' Regenerate object at 36: Yes 
' Regenerate object at 8: Yes 
' Regenerate object at 21: Yes 
' Regenerate object at 4: Yes 
' Regenerate object at 38: No 
' Regenerate object at 7: Yes 
' Regenerate object at 2: Yes 
' Regenerate object at 43: Yes 
' Regenerate object at 38: No 
' Cache size: 50, Regenerated: 94% 

Remarques

Une référence faible permet au garbage collector de collecter un objet tout en permettant une application à accéder à l’objet.A weak reference allows the garbage collector to collect an object while still allowing an application to access the object. Si vous avez besoin de l’objet, vous pouvez toujours obtenir une référence forte à celui-ci et l’empêcher d’être collecté.If you need the object, you can still obtain a strong reference to it and prevent it from being collected. Pour plus d’informations sur l’utilisation court et des références faibles longues, consultez références faibles.For more information about how to use short and long weak references, see Weak References.

Constructeurs

WeakReference() WeakReference() WeakReference() WeakReference()
WeakReference(Object) WeakReference(Object) WeakReference(Object) WeakReference(Object)

Initialise une nouvelle instance de la classe WeakReference, référençant l'objet spécifié. Initializes a new instance of the WeakReference class, referencing the specified object.

WeakReference(Object, Boolean) WeakReference(Object, Boolean) WeakReference(Object, Boolean) WeakReference(Object, Boolean)

Initialise une nouvelle instance de la classe WeakReference, référençant l'objet spécifié et utilisant le suivi d'activation spécifié. Initializes a new instance of the WeakReference class, referencing the specified object and using the specified resurrection tracking.

WeakReference(SerializationInfo, StreamingContext) WeakReference(SerializationInfo, StreamingContext) WeakReference(SerializationInfo, StreamingContext) WeakReference(SerializationInfo, StreamingContext)

Initialise une nouvelle instance de la classe WeakReference, à l'aide de données désérialisées provenant des objets de sérialisation et de flux spécifiés. Initializes a new instance of the WeakReference class, using deserialized data from the specified serialization and stream objects.

Propriétés

IsAlive IsAlive IsAlive IsAlive

Obtient une indication permettant de savoir si l'objet référencé par l'objet WeakReference a été récupéré par le garbage collector. Gets an indication whether the object referenced by the current WeakReference object has been garbage collected.

Target Target Target Target

Obtient ou définit l'objet (la cible) référencé par l'objet WeakReference actuel. Gets or sets the object (the target) referenced by the current WeakReference object.

TrackResurrection TrackResurrection TrackResurrection TrackResurrection

Indique si un suivi est effectué pour l'objet référencé par l'objet WeakReference en cours après sa finalisation. Gets an indication whether the object referenced by the current WeakReference object is tracked after it is finalized.

Méthodes

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Détermine si l'objet spécifié est identique à l'objet actuel. Determines whether the specified object is equal to the current object.

(Inherited from Object)
Finalize() Finalize() Finalize() Finalize()

Ignore la référence à la cible représentée par l'objet WeakReference actuel. Discards the reference to the target represented by the current WeakReference object.

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Fait office de fonction de hachage par défaut. Serves as the default hash function.

(Inherited from Object)
GetObjectData(SerializationInfo, StreamingContext) GetObjectData(SerializationInfo, StreamingContext) GetObjectData(SerializationInfo, StreamingContext) GetObjectData(SerializationInfo, StreamingContext)

Remplit un objet SerializationInfo de toutes les données nécessaires à la sérialisation de l'objet WeakReference en cours. Populates a SerializationInfo object with all the data needed to serialize the current WeakReference object.

GetType() GetType() GetType() GetType()

Obtient le Type de l'instance actuelle. Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Crée une copie superficielle du Object actuel. Creates a shallow copy of the current Object.

(Inherited from Object)
ToString() ToString() ToString() ToString()

Retourne une chaîne qui représente l'objet actuel. Returns a string that represents the current object.

(Inherited from Object)

Sécurité

SecurityPermission
pour avoir la possibilité d’appeler du code non managé. for the ability to call unmanaged code. Valeur de la demande : InheritanceDemand; Valeur d’autorisation : UnmanagedCode Demand value: InheritanceDemand; Permission value: UnmanagedCode

S’applique à

Voir aussi