有没有办法在CLR中执行WeakList或WeakCollection(如WeakReference)？

Question

使用一个List<WeakReference>将无法正常工作.我想要的是,只要他们引用的对象被垃圾收集,就会自动从列表中删除 WeakReferences .

ConditionalWeakTable<TKey,TValue> 也不满足我,因为虽然它的键和值被弱引用和收集,但你不能枚举它们!

Answer 1

我同意实施a WeakList<T>是可能的,但我认为这并不容易.欢迎您在此处使用我的实现.该WeakCollection<T>等级取决于WeakReference<T>,而这又取决于SafeGCHandle.

Answer 2

你可以轻松地实现一个WeakList<T>类,它将包装一个List<WeakReference>.

在垃圾收集时无法自动删除对象,因为无法检测到何时发生这种情况.但是,通过检查WeakReference.IsAlive属性,您可以在遇到它们时删除"死"(垃圾收集)对象.但是,我不推荐这种方法,因为从客户的角度来看,它可能导致令人困惑的行为.相反,我建议实现一个Purge方法来删除你明确调用的死项.

这是一个示例实现:

public class WeakList<T> : IList<T>
{
    private List<WeakReference<T>> _innerList = new List<WeakReference<T>>();

    #region IList<T> Members

    public int IndexOf(T item)
    {
        return _innerList.Select(wr => wr.Target).IndexOf(item);
    }

    public void Insert(int index, T item)
    {
        _innerList.Insert(index, new WeakReference<T>(item));
    }

    public void RemoveAt(int index)
    {
        _innerList.RemoveAt(index);
    }

    public T this[int index]
    {
        get
        {
            return _innerList[index].Target;
        }
        set
        {
            _innerList[index] = new WeakReference<T>(value);
        }
    }

    #endregion

    #region ICollection<T> Members

    public void Add(T item)
    {
        _innerList.Add(new WeakReference<T>(item));
    }

    public void Clear()
    {
        _innerList.Clear();
    }

    public bool Contains(T item)
    {
        return _innerList.Any(wr => object.Equals(wr.Target, item));
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        _innerList.Select(wr => wr.Target).CopyTo(array, arrayIndex);
    }

    public int Count
    {
        get { return _innerList.Count; }
    }

    public bool IsReadOnly
    {
        get { return false; }
    }

    public bool Remove(T item)
    {
        int index = IndexOf(item);
        if (index > -1)
        {
            RemoveAt(index);
            return true;
        }
        return false;
    }

    #endregion

    #region IEnumerable<T> Members

    public IEnumerator<T> GetEnumerator()
    {
        return _innerList.Select(x => x.Target).GetEnumerator();
    }

    #endregion

    #region IEnumerable Members

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }

    #endregion

    public void Purge()
    {
        _innerList.RemoveAll(wr => !wr.IsAlive);
    }
}

该类使用以下类和扩展方法:

WeakReference<T>(只是一个强类型的包装WeakReference)

[Serializable]
public class WeakReference<T> : WeakReference
{
    public WeakReference(T target)
        : base(target)
    {
    }

    public WeakReference(T target, bool trackResurrection)
        : base(target, trackResurrection)
    {
    }

    public WeakReference(SerializationInfo info, StreamingContext context)
        : base(info, context)
    {
    }

    public new T Target
    {
        get
        {
            return (T)base.Target;
        }
    }
}

IndexOf(同样如此IList<T>.IndexOf,但适用于IEnumerable<T>)

    public static int IndexOf<T>(this IEnumerable<T> source, T item)
    {
        var entry = source.Select((x, i) => new { Value = x, Index = i })
                    .Where(x => object.Equals(x.Value, item))
                    .FirstOrDefault();
        return entry != null ? entry.Index : -1;
    }

CopyTo(同样如此IList<T>.CopyTo,但适用于IEnumerable<T>)

    public static void CopyTo<T>(this IEnumerable<T> source, T[] array, int startIndex)
    {
        int lowerBound = array.GetLowerBound(0);
        int upperBound = array.GetUpperBound(0);
        if (startIndex < lowerBound)
            throw new ArgumentOutOfRangeException("startIndex", "The start index must be greater than or equal to the array lower bound");
        if (startIndex > upperBound)
            throw new ArgumentOutOfRangeException("startIndex", "The start index must be less than or equal to the array upper bound");

        int i = 0;
        foreach (var item in source)
        {
            if (startIndex + i > upperBound)
                throw new ArgumentException("The array capacity is insufficient to copy all items from the source sequence");
            array[startIndex + i] = item;
            i++;
        }
    }