您可以轻松实现 WeakList<T> 类，该类将包装 List<WeakReference>。
无法在垃圾回收时自动删除对象，因为无法检测到何时发生这种情况。但是，您可以通过检查WeakReference.IsAlive 属性在遇到“死”（垃圾收集）对象时删除它们。但是，我不推荐这种方法，因为从客户的角度来看，它可能会导致令人困惑的行为。相反，我建议实现一个 Purge 方法来删除死条目，您可以显式调用它。
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WeakReference 的强类型包装器）
[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（与IList<T>.IndexOf 相同，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（与IList<T>.CopyTo 相同，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++;
}
}