WeakReference WeakReference WeakReference WeakReference Class

Definition

Rappresenta un riferimento debole, ovvero un riferimento a un oggetto che può ancora essere recuperato dalla procedura di 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
Inheritance
WeakReferenceWeakReferenceWeakReferenceWeakReference
Attributes
ComVisibleAttribute SerializableAttribute
Implements

Examples

Nell'esempio seguente viene illustrato come è possibile usare riferimenti deboli per mantenere una cache di oggetti come una risorsa per un'applicazione.The following example demonstrates how you can use weak references to maintain a cache of objects as a resource for an application. La cache viene costruita usando un IDictionary<TKey,TValue> di WeakReference oggetti codificati da un valore di indice.The cache is constructed using an IDictionary<TKey,TValue> of WeakReference objects keyed by an index value. Il Target proprietà per il WeakReference oggetti è un oggetto in una matrice di byte che rappresenta i dati.The Target property for the WeakReference objects is an object in a byte array that represents data.

Nell'esempio si accede in modo casuale gli oggetti nella cache.The example randomly accesses objects in the cache. Se un oggetto viene recuperato per la garbage collection, un nuovo oggetto dati viene rigenerato. in caso contrario, l'oggetto è disponibile per l'accesso a causa il riferimento debole.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% 

Remarks

Un riferimento debole consente al garbage collector di raccogliere un oggetto senza tuttavia impedire all'applicazione accedere all'oggetto.A weak reference allows the garbage collector to collect an object while still allowing an application to access the object. Se è necessario l'oggetto, è possibile comunque ottenere un riferimento forte ad esso e impedire che venga raccolto.If you need the object, you can still obtain a strong reference to it and prevent it from being collected. Per altre informazioni su come usare brevi e i riferimenti deboli lunghi, vedere riferimenti deboli.For more information about how to use short and long weak references, see Weak References.

Constructors

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

Inizializza una nuova istanza della classe WeakReference che fa riferimento all'oggetto specificato. Initializes a new instance of the WeakReference class, referencing the specified object.

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

Inizializza una nuova istanza della classe WeakReference, che fa riferimento all'oggetto specificato e usa l'opzione di rilevamento specificata per il ripristino. 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)

Inizializza una nuova istanza della classe WeakReference, usando dati deserializzati dalla serializzazione e dagli oggetti del flusso specificati. Initializes a new instance of the WeakReference class, using deserialized data from the specified serialization and stream objects.

Properties

IsAlive IsAlive IsAlive IsAlive

Ottiene un valore che indica se l'oggetto cui fa riferimento l'oggetto WeakReference corrente è stato sottoposto alla procedura di Garbage Collection. Gets an indication whether the object referenced by the current WeakReference object has been garbage collected.

Target Target Target Target

Ottiene o imposta l'oggetto o la destinazione a cui fa riferimento l'oggetto WeakReference corrente. Gets or sets the object (the target) referenced by the current WeakReference object.

TrackResurrection TrackResurrection TrackResurrection TrackResurrection

Ottiene un valore che indica se l'oggetto cui fa riferimento l'oggetto WeakReference corrente viene controllato dopo essere stato finalizzato. Gets an indication whether the object referenced by the current WeakReference object is tracked after it is finalized.

Methods

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

Determina se l'oggetto specificato è uguale all'oggetto corrente. Determines whether the specified object is equal to the current object.

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

Elimina il riferimento alla destinazione rappresentata dall'oggetto WeakReference corrente. Discards the reference to the target represented by the current WeakReference object.

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

Funge da funzione hash predefinita. Serves as the default hash function.

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

Popola un oggetto SerializationInfo con tutti i dati necessari per serializzare l'oggetto WeakReference corrente. Populates a SerializationInfo object with all the data needed to serialize the current WeakReference object.

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

Ottiene l'oggetto Type dell'istanza corrente. Gets the Type of the current instance.

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

Crea una copia superficiale dell'oggetto Object corrente. Creates a shallow copy of the current Object.

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

Restituisce una stringa che rappresenta l'oggetto corrente. Returns a string that represents the current object.

(Inherited from Object)

Security

SecurityPermission
la possibilità di chiamare codice non gestito. for the ability to call unmanaged code. Valore richiesta: InheritanceDemand; Valore dell'autorizzazione: UnmanagedCode Demand value: InheritanceDemand; Permission value: UnmanagedCode

Applies to

See Also