在上面介紹過棧（Stack）的存儲結構，接下來介紹另一種存儲結構字典（Dictionary）。 字典（Dictionary）里面的每一個元素都是一個鍵值對(由二個元素組成：鍵和值) 鍵必須是唯一的,而值不需要唯一的,鍵和值都可以是任何類型。字典(Dictionary)是常用于查找和排序的列表。
接下來看一下Dictionary的部分方法和類的底層實現代碼：
1.Add：將指定的鍵和值添加到字典中。
public void Add(TKey key, TValue value) { Insert(key, value, true); } private void Insert(TKey key, TValue value, bool add) { if( key == null ) { ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key); } if (buckets == null) Initialize(0); int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF; int targetBucket = hashCode % buckets.Length; #if FEATURE_RANDOMIZED_STRING_HASHING int collisionCount = 0; #endif for (int i = buckets[targetBucket]; i >= 0; i = entries[i].next) { if (entries[i].hashCode == hashCode && comparer.Equals(entries[i].key, key)) { if (add) { ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_AddingDuplicate); } entries[i].value = value; version++; return; } #if FEATURE_RANDOMIZED_STRING_HASHING collisionCount++;#endif } int index; if (freeCount > 0) { index = freeList; freeList = entries[index].next; freeCount--; } else { if (count == entries.Length) { Resize(); targetBucket = hashCode % buckets.Length; } index = count; count++; } entries[index].hashCode = hashCode; entries[index].next = buckets[targetBucket]; entries[index].key = key; entries[index].value = value; buckets[targetBucket] = index; version++; #if FEATURE_RANDOMIZED_STRING_HASHING if(collisionCount > HashHelpers.HashCollisionThreshold && HashHelpers.IsWellKnownEqualityComparer(comparer)) { comparer = (IEqualityComparer<TKey>) HashHelpers.GetRandomizedEqualityComparer(comparer); Resize(entries.Length, true); } #endif }2.Clear()：從 Dictionary<TKey, TValue> 中移除所有的鍵和值。
public void Clear() { if (count > 0) { for (int i = 0; i < buckets.Length; i++) buckets[i] = -1; Array.Clear(entries, 0, count); freeList = -1; count = 0; freeCount = 0; version++; } }3.Remove()：從 Dictionary<TKey, TValue> 中移除所指定的鍵的值。
public bool Remove(TKey key) { if(key == null) { ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key); } if (buckets != null) { int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF; int bucket = hashCode % buckets.Length; int last = -1; for (int i = buckets[bucket]; i >= 0; last = i, i = entries[i].next) { if (entries[i].hashCode == hashCode && comparer.Equals(entries[i].key, key)) { if (last < 0) { buckets[bucket] = entries[i].next; } else { entries[last].next = entries[i].next; } entries[i].hashCode = -1; entries[i].next = freeList; entries[i].key = default(TKey); entries[i].value = default(TValue); freeList = i; freeCount++; version++; return true; } } } return false; }
4.GetEnumerator()：返回循環訪問 Dictionary<TKey, TValue> 的枚舉器。
public Enumerator GetEnumerator() { return new Enumerator(this, Enumerator.KeyValuePair); } [Serializable] public struct Enumerator: IEnumerator<KeyValuePair<TKey,TValue>>, IDictionaryEnumerator { private Dictionary<TKey,TValue> dictionary; private int version; private int index; private KeyValuePair<TKey,TValue> current; private int getEnumeratorRetType; // What should Enumerator.Current return? internal const int DictEntry = 1; internal const int KeyValuePair = 2; internal Enumerator(Dictionary<TKey,TValue> dictionary, int getEnumeratorRetType) { this.dictionary = dictionary; version = dictionary.version; index = 0; this.getEnumeratorRetType = getEnumeratorRetType; current = new KeyValuePair<TKey, TValue>(); } public bool MoveNext() { if (version != dictionary.version) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion); } // Use unsigned comparison since we set index to dictionary.count+1 when the enumeration ends. // dictionary.count+1 could be negative if dictionary.count is Int32.MaxValue while ((uint)index < (uint)dictionary.count) { if (dictionary.entries[index].hashCode >= 0) { current = new KeyValuePair<TKey, TValue>(dictionary.entries[index].key, dictionary.entries[index].value); index++; return true; } index++; } index = dictionary.count + 1; current = new KeyValuePair<TKey, TValue>(); return false; } public KeyValuePair<TKey,TValue> Current { get { return current; } } public void Dispose() { } object IEnumerator.Current { get { if( index == 0 || (index == dictionary.count + 1)) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumOpCantHappen); } if (getEnumeratorRetType == DictEntry) { return new System.Collections.DictionaryEntry(current.Key, current.Value); } else { return new KeyValuePair<TKey, TValue>(current.Key, current.Value); } } } void IEnumerator.Reset() { if (version != dictionary.version) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion); } index = 0; current = new KeyValuePair<TKey, TValue>(); } DictionaryEntry IDictionaryEnumerator.Entry { get { if( index == 0 || (index == dictionary.count + 1)) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumOpCantHappen); } return new DictionaryEntry(current.Key, current.Value); } } object IDictionaryEnumerator.Key { get { if( index == 0 || (index == dictionary.count + 1)) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumOpCantHappen); } return current.Key; } } object IDictionaryEnumerator.Value { get { if( index == 0 || (index == dictionary.count + 1)) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumOpCantHappen); } return current.Value; } } }上面主要是對字典(Dictionary)的一些常用方法進行一個簡單的說明。接下來主要闡述如何創建安全的字典(Dictionary)存儲結構。有關線程安全的部分，在這里就不再贅述了。
/// <summary> /// 線程安全通用字典 /// </summary> /// <typeparam name="TKey"></typeparam> /// <typeparam name="TValue"></typeparam> public class TDictionary<TKey, TValue> : IDictionary<TKey, TValue> { /// <summary> /// 鎖定字典 /// </summary> private readonly ReaderWriterLockSlim _lockDictionary = new ReaderWriterLockSlim(); /// <summary> ///基本字典 /// </summary> private readonly Dictionary<TKey, TValue> _mDictionary; // Variables /// <summary> /// 初始化字典對象 /// </summary> public TDictionary() { _mDictionary = new Dictionary<TKey, TValue>(); } /// <summary> /// 初始化字典對象 /// </summary> /// <param name="capacity">字典的初始容量</param> public TDictionary(int capacity) { _mDictionary = new Dictionary<TKey, TValue>(capacity); } /// <summary> ///初始化字典對象 /// </summary> /// <param name="comparer">比較器在比較鍵時使用</param> public TDictionary(IEqualityComparer<TKey> comparer) { _mDictionary = new Dictionary<TKey, TValue>(comparer); } /// <summary> /// 初始化字典對象 /// </summary> /// <param name="dictionary">其鍵和值被復制到此對象的字典</param> public TDictionary(IDictionary<TKey, TValue> dictionary) { _mDictionary = new Dictionary<TKey, TValue>(dictionary); } /// <summary> ///初始化字典對象 /// </summary> /// <param name="capacity">字典的初始容量</param> /// <param name="comparer">比較器在比較鍵時使用</param> public TDictionary(int capacity, IEqualityComparer<TKey> comparer) { _mDictionary = new Dictionary<TKey, TValue>(capacity, comparer); } /// <summary> /// 初始化字典對象 /// </summary> /// <param name="dictionary">其鍵和值被復制到此對象的字典</param> /// <param name="comparer">比較器在比較鍵時使用</param> public TDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer) { _mDictionary = new Dictionary<TKey, TValue>(dictionary, comparer); } public TValue GetValueAddIfNotExist(TKey key, Func<TValue> func) { return _lockDictionary.PerformUsingUpgradeableReadLock(() => { TValue rVal; // 如果我們有值，得到它并退出 if (_mDictionary.TryGetValue(key, out rVal)) return rVal; // 沒有找到，所以做函數得到的值 _lockDictionary.PerformUsingWriteLock(() => { rVal = func.Invoke(); // 添加到字典 _mDictionary.Add(key, rVal); return rVal; }); return rVal; }); } /// <summary> /// 將項目添加到字典 /// </summary> /// <param name="key">添加的關鍵</param> /// <param name="value">要添加的值</param> public void Add(TKey key, TValue value) { _lockDictionary.PerformUsingWriteLock(() => _mDictionary.Add(key, value)); } /// <summary> ///將項目添加到字典 /// </summary> /// <param name="item">要添加的鍵/值</param> public void Add(KeyValuePair<TKey, TValue> item) { var key = item.Key; var value = item.Value; _lockDictionary.PerformUsingWriteLock(() => _mDictionary.Add(key, value)); } /// <summary> /// 如果值不存在，則添加該值。 返回如果值已添加，則為true /// </summary> /// <param name="key">檢查的關鍵，添加</param> /// <param name="value">如果鍵不存在，則添加的值</param> public bool AddIfNotExists(TKey key, TValue value) { bool rVal = false; _lockDictionary.PerformUsingWriteLock(() => { // 如果不存在，則添加它 if (!_mDictionary.ContainsKey(key)) { // 添加該值并設置標志 _mDictionary.Add(key, value); rVal = true; } }); return rVal; } /// <summary> /// 如果鍵不存在，則添加值列表。 /// </summary> /// <param name="keys">要檢查的鍵，添加</param> /// <param name="defaultValue">如果鍵不存在，則添加的值</param> public void AddIfNotExists(IEnumerable<TKey> keys, TValue defaultValue) { _lockDictionary.PerformUsingWriteLock(() => { foreach (TKey key in keys) { // 如果不存在，則添加它 if (!_mDictionary.ContainsKey(key)) _mDictionary.Add(key, defaultValue); } }); } public bool AddIfNotExistsElseUpdate(TKey key, TValue value) { var rVal = false; _lockDictionary.PerformUsingWriteLock(() => { // 如果不存在，則添加它 if (!_mDictionary.ContainsKey(key)) { // 添加該值并設置標志 _mDictionary.Add(key, value); rVal = true; } else _mDictionary[key] = value; }); return rVal; } /// <summary> /// 如果鍵存在，則更新鍵的值。 /// </summary> /// <param name="key"></param> /// <param name="newValue"></param> public bool UpdateValueIfKeyExists(TKey key, TValue newValue) { bool rVal = false; _lockDictionary.PerformUsingWriteLock(() => { // 如果我們有密鑰，然后更新它 if (!_mDictionary.ContainsKey(key)) return; _mDictionary[key] = newValue; rVal = true; }); return rVal; } /// <summary> /// 如果鍵值對存在于字典中，則返回true /// </summary> /// <param name="item">鍵值對查找</param> public bool Contains(KeyValuePair<TKey, TValue> item) { return _lockDictionary.PerformUsingReadLock(() => ((_mDictionary.ContainsKey(item.Key)) && (_mDictionary.ContainsValue(item.Value)))); } public bool ContainsKey(TKey key) { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.ContainsKey(key)); } /// <summary> /// 如果字典包含此值，則返回true /// </summary> /// <param name="value">找到的值</param> public bool ContainsValue(TValue value) { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.ContainsValue(value)); } public ICollection<TKey> Keys { get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.Keys); } } public bool Remove(TKey key) { return _lockDictionary.PerformUsingWriteLock(() => (!_mDictionary.ContainsKey(key)) || _mDictionary.Remove(key)); } public bool Remove(KeyValuePair<TKey, TValue> item) { return _lockDictionary.PerformUsingWriteLock(() => { // 如果鍵不存在則跳過 TValue tempVal; if (!_mDictionary.TryGetValue(item.Key, out tempVal)) return false; //如果值不匹配，請跳過 return tempVal.Equals(item.Value) && _mDictionary.Remove(item.Key); }); } /// <summary> /// 從字典中刪除與模式匹配的項 /// </summary> /// <param name="predKey">基于鍵的可選表達式</param> /// <param name="predValue">基于值的選項表達式</param> public bool Remove(Predicate<TKey> predKey, Predicate<TValue> predValue) { return _lockDictionary.PerformUsingWriteLock(() => { // 如果沒有鍵退出 if (_mDictionary.Keys.Count == 0) return true; //保存要刪除的項目列表 var deleteList = new List<TKey>(); // 過程密鑰 foreach (var key in _mDictionary.Keys) { var isMatch = false; if (predKey != null) isMatch = (predKey(key)); // 如果此項目的值匹配，請添加它 if ((!isMatch) && (predValue != null) && (predValue(_mDictionary[key]))) isMatch = true; // 如果我們有匹配，添加到列表 if (isMatch) deleteList.Add(key); } // 從列表中刪除所有項目 foreach (var item in deleteList) _mDictionary.Remove(item); return true; }); } public bool TryGetValue(TKey key, out TValue value) { _lockDictionary.EnterReadLock(); try { return _mDictionary.TryGetValue(key, out value); } finally { _lockDictionary.ExitReadLock(); } } public ICollection<TValue> Values { get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.Values); } } public TValue this[TKey key] { get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary[key]); } set { _lockDictionary.PerformUsingWriteLock(() => _mDictionary[key] = value); } } /// <summary> /// 清除字典 /// </summary> public void Clear() { _lockDictionary.PerformUsingWriteLock(() => _mDictionary.Clear()); } public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) { _lockDictionary.PerformUsingReadLock(() => _mDictionary.ToArray().CopyTo(array, arrayIndex)); } /// <summary> /// 返回字典中的項目數 /// </summary> public int Count { get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.Count); } } public bool IsReadOnly { get { return false; } } public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() { Dictionary<TKey, TValue> localDict = null; _lockDictionary.PerformUsingReadLock(() => localDict = new Dictionary<TKey, TValue>(_mDictionary)); return ((IEnumerable<KeyValuePair<TKey, TValue>>)localDict).GetEnumerator(); } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { Dictionary<TKey, TValue> localDict = null; _lockDictionary.PerformUsingReadLock(() => localDict = new Dictionary<TKey, TValue>(_mDictionary)); return localDict.GetEnumerator(); } }以上創建安全的字典方法中，主要對字典的一些方法和屬性進行重寫操作，對某些方法進行鎖設置。
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