我正在尝试为.NET 4.0创建一个自定义的ReadOnlyDictionary<TKey, TValue>。方法是保持一个私有的Dictionary<TKey, TValue>对象,以及用于确定是否允许添加/删除和项目分配的标志。
这很好用,但我想实现IDictionary<TKey, TValue>接口以完整性。然而,我注意到它扩展了ICollection<KeyValuePair<TKey, TValue>>,而它的属性或方法没有出现在Dictionary<TKey, TValue>类中。这怎么可能?如果实现了接口,为什么ICollection成员不被公开呢?
此外,为什么Dictionary类需要首先实现ICollection?
下面是一个粗略的实现:
这很好用,但我想实现IDictionary<TKey, TValue>接口以完整性。然而,我注意到它扩展了ICollection<KeyValuePair<TKey, TValue>>,而它的属性或方法没有出现在Dictionary<TKey, TValue>类中。这怎么可能?如果实现了接口,为什么ICollection成员不被公开呢?
此外,为什么Dictionary类需要首先实现ICollection?
下面是一个粗略的实现:
public sealed class ReadOnlyDictionary<TKey, TValue>:
//IDictionary<TKey, TValue>,
IEnumerable<KeyValuePair<TKey, TValue>>
{
#region Members.
public bool AllowListEdit { get; private set; }
public bool AllowItemEdit { get; private set; }
private Dictionary<TKey, TValue> Dictionary { get; set; }
#endregion Members.
#region Constructors.
public ReadOnlyDictionary (bool allowListEdit, bool allowItemEdit) { this.AllowListEdit = allowListEdit; this.AllowItemEdit = allowItemEdit; this.Dictionary = new Dictionary<TKey, TValue>(); }
public ReadOnlyDictionary (IEqualityComparer<TKey> comparer, bool allowListEdit, bool allowItemEdit) { this.AllowListEdit = allowListEdit; this.AllowItemEdit = allowItemEdit; this.Dictionary = new Dictionary<TKey, TValue>(comparer); }
public ReadOnlyDictionary (IDictionary<TKey, TValue> dictionary, bool allowListEdit = false, bool allowItemEdit = false) : this(allowListEdit, allowItemEdit) { foreach (var pair in dictionary) { this.Dictionary.Add(pair.Key, pair.Value); } }
public ReadOnlyDictionary (IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer, bool allowListEdit = false, bool allowItemEdit = false) : this(comparer, allowListEdit, allowItemEdit) { foreach (var pair in dictionary) { this.Dictionary.Add(pair.Key, pair.Value); } }
#endregion Constructors.
#region Properties.
public int Count { get { return (this.Dictionary.Count); } }
public IEqualityComparer<TKey> Comparer { get { return (this.Dictionary.Comparer); } }
#endregion Properties.
#region Methods.
private void ThrowItemReadOnlyException () { if (this.AllowListEdit) { throw (new NotSupportedException("This collection does not allow editing items.")); } }
private void ThrowListReadOnlyException () { if (this.AllowItemEdit) { throw (new NotSupportedException("This collection does not allow adding and removing items.")); } }
public bool ContainsValue (TValue value) { return (this.Dictionary.ContainsValue(value)); }
public void Clear () { this.ThrowListReadOnlyException(); this.Dictionary.Clear(); }
#endregion Methods.
#region Interface Implementation: IEnumerable<KeyValuePair<TKey, TValue>>.
IEnumerator IEnumerable.GetEnumerator () { return (this.Dictionary.GetEnumerator()); }
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator () { return (this.Dictionary.GetEnumerator()); }
#endregion Interface Implementation: IEnumerable<KeyValuePair<TKey, TValue>>.
#region Interface Implementation: ICollection<KeyValuePair<TKey, TValue>>.
//public int Count { get { return (this.Dictionary.Count); } }
//public bool IsReadOnly { get { return (this.AllowListEdit); } }
//public bool Contains (KeyValuePair<TKey, TValue> item) { throw (new NotImplementedException()); }
//public void Clear () { throw (new NotImplementedException()); }
//public void Add (KeyValuePair<TKey, TValue> item) { throw (new NotImplementedException()); }
//public void CopyTo (KeyValuePair<TKey, TValue> [] array, int arrayIndex) { throw (new NotImplementedException()); }
//public bool Remove (KeyValuePair<TKey, TValue> item) { throw (new NotImplementedException()); }
#endregion Interface Implementation: ICollection<KeyValuePair<TKey, TValue>>.
#region Interface Implementation: IDictionary<TKey, TValue>.
//====================================================================================================
// Interface Implementation: IDictionary<TKey, TValue>.
//====================================================================================================
public Dictionary<TKey, TValue>.KeyCollection Keys { get { return (this.Dictionary.Keys); } }
public Dictionary<TKey, TValue>.ValueCollection Values { get { return (this.Dictionary.Values); } }
public TValue this [TKey key] { get { return (this.Dictionary [key]); } set { this.ThrowItemReadOnlyException(); this.Dictionary [key] = value; } }
public void Add (TKey key, TValue value) { this.ThrowListReadOnlyException(); this.Dictionary.Add(key, value); }
public bool ContainsKey (TKey key) { return (this.Dictionary.ContainsKey(key)); }
public bool Remove (TKey key) { this.ThrowListReadOnlyException(); return (this.Dictionary.Remove(key)); }
public bool TryGetValue (TKey key, out TValue value) { return (this.Dictionary.TryGetValue(key, out value)); }
#endregion Interface Implementation: IDictionary<TKey, TValue>.
}
ICollection
的很多优势。或许只是为了完整性和一致性(因为几乎所有在System.Collections
中的集合都扩展了ICollection
)? - dcastroICollection
或ICollection<T>
可以报告这个信息,但IEnumerable<T>
不行。在设计Dictionary
时,继承自IEnumerable<T>
和具有Count
方法的某些东西的最不具体的接口是ICollection<T>
。 - supercat