WeakReference Classe

Definição

public ref class WeakReference

public ref class WeakReference : System::Runtime::Serialization::ISerializable

public class WeakReference

public class WeakReference : System.Runtime.Serialization.ISerializable

[System.Serializable]
public class WeakReference : System.Runtime.Serialization.ISerializable

[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public class WeakReference : System.Runtime.Serialization.ISerializable

type WeakReference = class

type WeakReference = class
    interface ISerializable

[<System.Serializable>]
type WeakReference = class
    interface ISerializable

[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type WeakReference = class
    interface ISerializable

Public Class WeakReference

Public Class WeakReference
Implements ISerializable

Herança

Object

WeakReference

Atributos

SerializableAttribute ComVisibleAttribute

Implementações

ISerializable

Exemplos

O exemplo a seguir demonstra como você pode usar referências fracas para manter um cache de objetos como um recurso para um aplicativo. O cache é construído usando um IDictionary<TKey,TValue> dos WeakReference objetos chaveados por um valor de índice. A Target propriedade para os WeakReference objetos é um objeto em uma matriz de bytes que representa dados.

O exemplo acessa aleatoriamente objetos no cache. Se um objeto for recuperado para coleta de lixo, um novo objeto de dados será regenerado; caso contrário, o objeto está disponível para acesso devido à referência fraca.

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%

open System
open System.Collections.Generic

// This class creates byte arrays to simulate data.
type Data(size) =
    let _data = Array.zeroCreate<byte> (size * 1024)
    
    // Simple property.
    member _.Name = 
        string size

type Cache(count) =
    // Dictionary to contain the cache.
    static let mutable _cache = Dictionary<int, WeakReference>()

    // Track the number of times an object is regenerated.
    let mutable regenCount = 0

    do
        _cache <- Dictionary<int, WeakReference>()
        // Add objects with a short weak reference to the cache.
        for i = 0 to count - 1 do
            _cache.Add(i, WeakReference(Data i, false))

    // Number of items in the cache.
    member _.Count =
        _cache.Count

    // Number of times an object needs to be regenerated.
    member _.RegenerationCount =
        regenCount

    // Retrieve a data object from the cache.
    member _.Item
        with get (index) =
            match _cache[index].Target with
            | :? Data as d->
                // Object was obtained with the weak reference.
                printfn $"Regenerate object at {index}: No"
                d
            | _ ->
                // If the object was reclaimed, generate a new one.
                printfn $"Regenerate object at {index}: Yes"
                let d = Data index
                _cache[index].Target <- d
                regenCount <- regenCount + 1
                d 

// Create the cache.
let cacheSize = 50
let r = Random()
let c = Cache cacheSize

let mutable dataName = ""
GC.Collect 0

// Randomly access objects in the cache.
for _ = 0 to c.Count - 1 do
    let index = r.Next c.Count

    // Access the object by getting a property value.
    dataName <- c[index].Name

// Show results.
let regenPercent = double c.RegenerationCount / double c.Count
printfn $"Cache size: {c.Count}, Regenerated: {regenPercent:P2}%%"

// 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%

Comentários

Uma referência fraca permite que o coletor de lixo colete um objeto enquanto ainda permite que um aplicativo acesse o objeto. Se você precisar do objeto, ainda poderá obter uma referência forte a ele e impedir que ele seja coletado. Para obter mais informações sobre como usar referências fracas curtas e longas, consulte Referências Fracas.

Construtores

Propriedades

Métodos

Aplica-se a

Confira também

• GC
• Referências fracas