WeakReference WeakReference WeakReference WeakReference Class

Definice

Představuje Slabý odkaz, který odkazuje na objekt, zatímco stále umožňuje, aby byl objekt uvolněn uvolňováním paměti.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)]
[System.Serializable]
public class WeakReference : System.Runtime.Serialization.ISerializable
type WeakReference = class
    interface ISerializable
Public Class WeakReference
Implements ISerializable
Dědičnost
WeakReferenceWeakReferenceWeakReferenceWeakReference
Atributy
Implementuje

Příklady

Následující příklad ukazuje, jak lze pomocí slabých odkazů uchovávat mezipaměť objektů jako prostředek pro aplikaci.The following example demonstrates how you can use weak references to maintain a cache of objects as a resource for an application. Mezipaměť je vytvořena pomocí objektu IDictionary<TKey,TValue> WeakReference s klíčem, který je v hodnotě indexu.The cache is constructed using an IDictionary<TKey,TValue> of WeakReference objects keyed by an index value. Target VlastnostWeakReference pro objekty je objekt v bajtovém poli, které představuje data.The Target property for the WeakReference objects is an object in a byte array that represents data.

Příklad náhodně přistupuje k objektům v mezipaměti.The example randomly accesses objects in the cache. Pokud je objekt uvolněn pro uvolňování paměti, nový datový objekt se znovu vygeneruje. v opačném případě je objekt k dispozici pro přístup z důvodu slabého odkazu.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% 

Poznámky

Slabý odkaz umožňuje, aby systém uvolňování paměti shromáždil objekt, zatímco aplikace stále umožňuje přístup k objektu.A weak reference allows the garbage collector to collect an object while still allowing an application to access the object. Pokud objekt potřebujete, můžete k němu stále získat silný odkaz a zabránit jeho shromažďování.If you need the object, you can still obtain a strong reference to it and prevent it from being collected. Další informace o použití krátkých a dlouhých slabých odkazů najdete v tématu slabé odkazy.For more information about how to use short and long weak references, see Weak References.

Konstruktory

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

Inicializuje novou instanci WeakReference třídy odkazující na zadaný objekt.Initializes a new instance of the WeakReference class, referencing the specified object.

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

Inicializuje novou instanci WeakReference třídy s odkazem na zadaný objekt a pomocí zadaného sledování Resurrection.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)

Inicializuje novou instanci WeakReference třídy pomocí deserializovaných dat z určeného serializace a objektů streamu.Initializes a new instance of the WeakReference class, using deserialized data from the specified serialization and stream objects.

Vlastnosti

IsAlive IsAlive IsAlive IsAlive

Získá označení, zda byl objekt odkazovaný aktuálním WeakReference objektem uvolněn z paměti.Gets an indication whether the object referenced by the current WeakReference object has been garbage collected.

Target Target Target Target

Získá nebo nastaví objekt (cíl), na který odkazuje aktuální WeakReference objekt.Gets or sets the object (the target) referenced by the current WeakReference object.

TrackResurrection TrackResurrection TrackResurrection TrackResurrection

Získá indikaci, zda je objekt odkazovaný aktuálním WeakReference objektem sledován poté, co je finalizován.Gets an indication whether the object referenced by the current WeakReference object is tracked after it is finalized.

Metody

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

Určuje, zda se zadaný objekt rovná aktuálnímu objektu.Determines whether the specified object is equal to the current object.

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

Zahodí odkaz na cíl reprezentovaný aktuálním WeakReference objektem.Discards the reference to the target represented by the current WeakReference object.

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

Slouží jako výchozí funkce hash.Serves as the default hash function.

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

Naplní WeakReference objekt všemi daty potřebnými k serializaci aktuálního objektu. SerializationInfoPopulates a SerializationInfo object with all the data needed to serialize the current WeakReference object.

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

Získá Type aktuální instance.Gets the Type of the current instance.

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

Vytvoří Mělkou kopii aktuální Object.Creates a shallow copy of the current Object.

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

Vrací řetězec, který představuje aktuální objekt.Returns a string that represents the current object.

(Inherited from Object)

Zabezpečení

SecurityPermission
pro možnost volání nespravovaného kódu.for the ability to call unmanaged code. Hodnota poptávky: InheritanceDemand; Hodnota oprávnění:UnmanagedCodeDemand value: InheritanceDemand; Permission value: UnmanagedCode

Platí pro

Viz také