不变词典

我想你需要一门课程来包装 Dictionary ReadOnlyCollection 包裹 List .

虽然找不到执行此操作的默认类,但您会在以下问题的答案之一中找到一个实现: this 问题。

BCL Extras Project 还包含这样一个实现。它支持创建代理对象,该代理对象实现 IDictionary 并且可以在它的位置上使用。

.Net 4.5:System.Collections.ObjectModel.ReadOnlyDictionary

继承自 System.Collections.ObjectModel.KeyedCollection<TKey,TItem>

推翻 InsertItem 和 RemoveItem

C#并没有提供一种完全按照您建议的方式来实现这一点的方法,但是您可以返回一个“自制”的不可变字典,它可以包装您的myDictionary。

有关创建不可变字典的更多信息,请查看此文档。

Does C# have a way of giving me an immutable Dictionary?

如果提供此不可变词典的目的是保护您自己的词典,只需给它们一个浅拷贝即可。

public Dictionary<string, IMyObject> MyDictionary 
{ 
    get { return new Dictionary<string, IMyObject>(_myDictionary); } 
} 

当然,调用方仍然可以访问字典中的内容,并且可能会对它们进行变异。如果这是一个问题,做一个深度拷贝。

/// <summary>
/// Read only wrapper for generics based dictionary.
/// Only provides lookup retrieval abilities.
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <typeparam name="TValue"></typeparam>
public class DictionaryReadOnly<TKey, TValue> : IDictionary<TKey, TValue>
{
    #region Private Members

    private IDictionary<TKey, TValue> _item;
    private bool _throwOnWritableAction = false;

    #endregion

    #region Constructors

    /// <summary>
    /// Constructor requiring the generic dictionary being wrapped.
    /// </summary>
    /// <param name="item"></param>
    public DictionaryReadOnly(IDictionary<TKey, TValue> items)
    {
        _throwOnWritableAction = true;
        _item = items;
    }

    /// <summary>
    /// Constructor requiring the generic dictionary being wrapped.
    /// </summary>
    /// <param name="item"></param>
    public DictionaryReadOnly(IDictionary<TKey, TValue> items, bool throwOnWritableAction)
    {            
        _throwOnWritableAction = throwOnWritableAction;
        _item = items;
    }
    #endregion

    #region IDictionary<TKey,TValue> Members

    /// <summary>
    /// Number of items in the dictionary.
    /// </summary>
    public int Count
    {
        get { return _item.Count; }
    }

    /// <summary>
    /// Determine if the underlying collection contains the key.
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    public bool ContainsKey(TKey key)
    {
        return _item.ContainsKey(key);
    }

    /// <summary>
    /// Returns the value associated with the key.
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    public TValue this[TKey key]
    {
        get { return _item[key]; }
        set
        {
            CheckAndThrow("Set");
        }
    }

    /// <summary>
    /// Return keys.
    /// </summary>
    public ICollection<TKey> Keys
    {
        get { return _item.Keys; }
    }

    /// <summary>
    /// Not-supported.
    /// </summary>
    /// <param name="key"></param>
    /// <param name="value"></param>
    public void Add(TKey key, TValue value)
    {
        CheckAndThrow("Add");
    }

    /// <summary>
    /// Not-supported.
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    public bool Remove(TKey key)
    {
        CheckAndThrow("Remove");
        return false;
    }

    /// <summary>
    /// Try to get the value.
    /// </summary>
    /// <param name="key"></param>
    /// <param name="value"></param>
    /// <returns></returns>
    public bool TryGetValue(TKey key, out TValue value)
    {
        value = default(TValue);

        if (_item.ContainsKey(key))
        {
            value = _item[key];
            return true;
        }
        return false;
    }

    /// <summary>
    /// Get the values.
    /// </summary>
    public ICollection<TValue> Values
    {
        get { return _item.Values; }
    }

    #endregion

    #region ICollection<KeyValuePair<TKey,TValue>> Members

    /// <summary>
    /// Not-supported.
    /// </summary>
    /// <param name="item"></param>
    public void Add(KeyValuePair<TKey, TValue> item)
    {
        CheckAndThrow("Add");
    }

    /// <summary>
    /// Not-Supported.
    /// </summary>
    public void Clear()
    {
        CheckAndThrow("Clear");
    }

    /// <summary>
    /// Determine whether key value pair is in dictionary.
    /// </summary>
    /// <param name="item"></param>
    /// <returns></returns>
    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
        return _item.Contains(item);
    }

    /// <summary>
    /// Copy items to the array.
    /// </summary>
    /// <param name="array"></param>
    /// <param name="arrayIndex"></param>
    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
        this._item.CopyTo(array, arrayIndex);
    }

    /// <summary>
    /// Indicate read-only
    /// </summary>
    public bool IsReadOnly
    {
        get { return true; }
    }

    /// <summary>
    /// Non-supported action.
    /// </summary>
    /// <param name="item"></param>
    /// <returns></returns>
    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
        CheckAndThrow("Remove");
        return false;
    }

    #endregion

    #region IEnumerable<KeyValuePair<TKey,TValue>> Members
    /// <summary>
    /// Get the enumerator.
    /// </summary>
    /// <returns></returns>
    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
        return _item.GetEnumerator();
    }

    #endregion

    #region IEnumerable Members
    /// <summary>
    /// Get the enumerator.
    /// </summary>
    /// <returns></returns>
    IEnumerator IEnumerable.GetEnumerator()
    {
        return _item.GetEnumerator();
    }

    #endregion

    /// <summary>
    /// Check and thrown based on flag.
    /// </summary>
    /// <param name="action"></param>
    void CheckAndThrow(string action)
    {
        if (_throwOnWritableAction)
            throw new InvalidOperationException("Can not perform action : " + action + " on this read-only collection.");
    }
}