如何将方法对Dictionary的引用作为只读返回?

public class ReadOnlyDictionary<T, U>
{
    private IDictionary<T, U> BackingStore;

    public ReadOnlyDictionary<T, U>(IDictionary<T, U> baseDictionary) {
        this.BackingStore = baseDictionary;
    }

    public U this[T index] { get { return BackingStore[index]; } }

    // provide whatever other methods and/or interfaces you need
}

ReadOnlyDictionary<int, Employee> readOnlyDict = GetDictionaryHoweverYouLike();
ReadOnlyDictionary[5].EmployeeName = "Ooops"

为此,您还需要将值包装在只读包装器类中。

这是我为所有需要现成代码段的人使用的实现。如前所述,这只会使字典只读,而不会使其中的对象只读!

/// <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.");
    }
}

IEnumerable

IDictionary<TKey, TValue> Add .

公开枚举(IEnumerable)。

编辑:

class A : IEnumerable<B>
{
  ...
  public IEnumerator<B> GetEnumerator ( )
  {
    return _dictionary.GetEnumerator ( );
  }
  private Dictionary<B> _dictionary;
}