为什么在 C# 中实现通用 OrderedDictionary？

实现通用的 OrderedDictionary 并不是特别困难，但它不必要地耗费时间，坦率地说，这个类是 Microsoft 的一个巨大疏忽。有多种方法可以实现此目的，但我选择使用 KeyedCollection 作为内部存储。我还选择实现各种方法来对 List 进行排序。确实如此，因为这本质上是 IList 和 IDictionary 的混合体。

这是界面。请注意，它包括 System.Collections.Specialized.IOrderedDictionary，这是 Microsoft 提供的此接口的非通用版本。

// https://choosealicense.com/licenses/unlicense
// 或 https://choosealicense.com/licenses/mit/
使用系统;
使用System.Collections.Generic;
using System.Collections.Specialized;

命名空间 mattmc3.Common.Collections.Generic {

public interface IOrderedDictionary<tkey tvalue> : IDictionary<tkey tvalue>, IOrderedDictionary {
    new TValue this[int index] { get; set; }
    new TValue this[TKey key] { get; set; }
    new int Count { get; }
    new ICollection<tkey> Keys { get; }
    new ICollection<tvalue> Values { get; }
    new void Add(TKey key, TValue value);
    new void Clear();
    void Insert(int index, TKey key, TValue value);
    int IndexOf(TKey key);
    bool ContainsValue(TValue value);
    bool ContainsValue(TValue value, IEqualityComparer<tvalue> comparer);
    new bool ContainsKey(TKey key);
    new IEnumerator<keyvaluepair tvalue>> GetEnumerator();
    new bool Remove(TKey key);
    new void RemoveAt(int index);
    new bool TryGetValue(TKey key, out TValue value);
    TValue GetValue(TKey key);
    void SetValue(TKey key, TValue value);
    KeyValuePair<tkey tvalue> GetItem(int index);
    void SetItem(int index, TValue value);
}
</tkey></keyvaluepair></tvalue></tvalue></tkey></tkey></tkey>

}
这是与帮助程序一起的实现类：

// http://unlicense.org
使用 System;
使用 System.Collections.ObjectModel;
使用 System.Diagnostics;
使用 System.Collections;
使用 System.Collections.Specialized;
使用 System.Collections.Generic;
使用System.Linq;

命名空间 mattmc3.Common.Collections.Generic {

/// <summary>
/// A dictionary object that allows rapid hash lookups using keys, but also
/// maintains the key insertion order so that values can be retrieved by
/// key index.
/// </summary>
public class OrderedDictionary<tkey tvalue> : IOrderedDictionary<tkey tvalue> {

    #region Fields/Properties

    private KeyedCollection2<tkey keyvaluepair tvalue>> _keyedCollection;

    /// <summary>
    /// Gets or sets the value associated with the specified key.
    /// </summary>
    /// <param name='"key"'>The key associated with the value to get or set.
    public TValue this[TKey key] {
        get {
            return GetValue(key);
        }
        set {
            SetValue(key, value);
        }
    }

    /// <summary>
    /// Gets or sets the value at the specified index.
    /// </summary>
    /// <param name='"index"'>The index of the value to get or set.
    public TValue this[int index] {
        get {
            return GetItem(index).Value;
        }
        set {
            SetItem(index, value);
        }
    }

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

    public ICollection<tkey> Keys {
        get {
            return _keyedCollection.Select(x => x.Key).ToList();
        }
    }

    public ICollection<tvalue> Values {
        get {
            return _keyedCollection.Select(x => x.Value).ToList();
        }
    }

    public IEqualityComparer<tkey> Comparer {
        get;
        private set;
    }

    #endregion

    #region Constructors

    public OrderedDictionary() {
        Initialize();
    }

    public OrderedDictionary(IEqualityComparer<tkey> comparer) {
        Initialize(comparer);
    }

    public OrderedDictionary(IOrderedDictionary<tkey tvalue> dictionary) {
        Initialize();
        foreach (KeyValuePair<tkey tvalue> pair in dictionary) {
            _keyedCollection.Add(pair);
        }
    }

    public OrderedDictionary(IOrderedDictionary<tkey tvalue> dictionary, IEqualityComparer<tkey> comparer) {
        Initialize(comparer);
        foreach (KeyValuePair<tkey tvalue> pair in dictionary) {
            _keyedCollection.Add(pair);
        }
    }

    #endregion

    #region Methods

    private void Initialize(IEqualityComparer<tkey> comparer = null) {
        this.Comparer = comparer;
        if (comparer != null) {
            _keyedCollection = new KeyedCollection2<tkey keyvaluepair tvalue>>(x => x.Key, comparer);
        }
        else {
            _keyedCollection = new KeyedCollection2<tkey keyvaluepair tvalue>>(x => x.Key);
        }
    }

    public void Add(TKey key, TValue value) {
        _keyedCollection.Add(new KeyValuePair<tkey tvalue>(key, value));
    }

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

    public void Insert(int index, TKey key, TValue value) {
        _keyedCollection.Insert(index, new KeyValuePair<tkey tvalue>(key, value));
    }

    public int IndexOf(TKey key) {
        if (_keyedCollection.Contains(key)) {
            return _keyedCollection.IndexOf(_keyedCollection[key]);
        }
        else {
            return -1;
        }
    }

    public bool ContainsValue(TValue value) {
        return this.Values.Contains(value);
    }

    public bool ContainsValue(TValue value, IEqualityComparer<tvalue> comparer) {
        return this.Values.Contains(value, comparer);
    }

    public bool ContainsKey(TKey key) {
        return _keyedCollection.Contains(key);
    }

    public KeyValuePair<tkey tvalue> GetItem(int index) {
        if (index = _keyedCollection.Count) {
            throw new ArgumentException(String.Format("The index was outside the bounds of the dictionary: {0}", index));
        }
        return _keyedCollection[index];
    }

    /// <summary>
    /// Sets the value at the index specified.
    /// </summary>
    /// <param name='"index"'>The index of the value desired
    /// <param name='"value"'>The value to set
    /// <exception cref='"ArgumentOutOfRangeException"'>
    /// Thrown when the index specified does not refer to a KeyValuePair in this object
    /// </exception>
    public void SetItem(int index, TValue value) {
        if (index = _keyedCollection.Count) {
            throw new ArgumentException("The index is outside the bounds of the dictionary: {0}".FormatWith(index));
        }
        var kvp = new KeyValuePair<tkey tvalue>(_keyedCollection[index].Key, value);
        _keyedCollection[index] = kvp;
    }

    public IEnumerator<keyvaluepair tvalue>> GetEnumerator() {
        return _keyedCollection.GetEnumerator();
    }

    public bool Remove(TKey key) {
        return _keyedCollection.Remove(key);
    }

    public void RemoveAt(int index</keyvaluepair></tkey></tkey></tvalue></tkey></tkey></tkey></tkey></tkey></tkey></tkey></tkey></tkey></tkey></tkey></tkey></tvalue></tkey></tkey></tkey></tkey>

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