在上面介绍过栈（Stack）的存储结构，接下来介绍另一种存储结构字典（Dictionary）。 字典（Dictionary）里面的每一个元素都是一个键值对(由二个元素组成：键和值) 键必须是唯一的,而值不需要唯一的,键和值都可以是任何类型。字典(Dictionary)是常用于查找和排序的列表。
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接下来看一下Dictionary的部分方法和类的底层实现代码：
1.Add：将指定的键和值添加到字典中。
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) HashHelpers.GetRandomizedEqualityComparer(comparer);
Resize(entries.Length, true);
}
#endif
} 2.Clear()：从 Dictionary 中移除所有的键和值。
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()：从 Dictionary 中移除所指定的键的值。
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()：返回循环访问 Dictionary 的枚举器。
public Enumerator GetEnumerator() { return new Enumerator(this, Enumerator.KeyValuePair);
}[Serializable]
public struct Enumerator: IEnumerator>,
IDictionaryEnumerator
{
private Dictionary dictionary;
private int version;
private int index;
private KeyValuePair current;
private int getEnumeratorRetType; // What should Enumerator.Current return?
internal const int DictEntry = 1;
internal const int KeyValuePair = 2;
internal Enumerator(Dictionary dictionary, int getEnumeratorRetType) {
this.dictionary = dictionary;
version = dictionary.version;
index = 0;
this.getEnumeratorRetType = getEnumeratorRetType;
current = new KeyValuePair();
}
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(dictionary.entries[index].key, dictionary.entries[index].value);
index++;
return true;
}
index++;
}
index = dictionary.count + 1;
current = new KeyValuePair();
return false;
}
public KeyValuePair 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(current.Key, current.Value);
}
}
}
void IEnumerator.Reset() {
if (version != dictionary.version) {
ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion);
}
index = 0;
current = new KeyValuePair();
}
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;
}
}
}
上面主要是对字典(Dictionary)的一些常用方法进行一个简单的说明。接下来主要阐述如何创建安全的字典(Dictionary)存储结构。有关线程安全的部分，在这里就不再赘述了。
///
/// 线程安全通用字典
///
///
///
public class TDictionary : IDictionary
{
///
/// 锁定字典
///
private readonly ReaderWriterLockSlim _lockDictionary = new ReaderWriterLockSlim();
///
///基本字典
///
private readonly Dictionary _mDictionary;
// Variables
///
/// 初始化字典对象
///
public TDictionary()
{
_mDictionary = new Dictionary();
}
///
/// 初始化字典对象
///
/// 字典的初始容量
public TDictionary(int capacity)
{
_mDictionary = new Dictionary(capacity);
}
///
///初始化字典对象
///
/// 比较器在比较键时使用
public TDictionary(IEqualityComparer comparer)
{
_mDictionary = new Dictionary(comparer);
}
///
/// 初始化字典对象
///
/// 其键和值被复制到此对象的字典
public TDictionary(IDictionary dictionary)
{
_mDictionary = new Dictionary(dictionary);
}
///
///初始化字典对象
///
/// 字典的初始容量
/// 比较器在比较键时使用
public TDictionary(int capacity, IEqualityComparer comparer)
{
_mDictionary = new Dictionary(capacity, comparer);
}
///
/// 初始化字典对象
///
/// 其键和值被复制到此对象的字典
/// 比较器在比较键时使用
public TDictionary(IDictionary dictionary, IEqualityComparer comparer)
{
_mDictionary = new Dictionary(dictionary, comparer);
}
///
/// 返回的值. 如果 不存在被执行并添加到字典
///
/// 检查的关键
/// 如果键不存在，委托调用
public TValue GetValueAddIfNotExist(TKey key, Func func)
{
// 输入写锁，使绝对确定密钥从我们检查它是否存在的时候添加/删除
//到我们添加它的时间，如果它不存在
return _lockDictionary.PerformUsingUpgradeableReadLock(() =>
{
TValue rVal;
// 如果我们有值，得到它并退出
if (_mDictionary.TryGetValue(key, out rVal))
return rVal;
// 没有找到，所以做函数得到的值
_lockDictionary.PerformUsingWriteLock(() =>
{
rVal = func.Invoke();
// 添加到字典
_mDictionary.Add(key, rVal);
return rVal;
});
return rVal;
});
}
///
/// 将项目添加到字典
///
/// 添加的关键
/// 要添加的值
public void Add(TKey key, TValue value)
{
_lockDictionary.PerformUsingWriteLock(() => _mDictionary.Add(key, value));
}
///
///将项目添加到字典
///
/// 要添加的键/值
public void Add(KeyValuePair item)
{
var key = item.Key;
var value = item.Value;
_lockDictionary.PerformUsingWriteLock(() => _mDictionary.Add(key, value));
}
///
/// 如果值不存在，则添加该值。 返回如果值已添加，则为true
///
/// 检查的关键，添加
/// 如果键不存在，则添加的值
public bool AddIfNotExists(TKey key, TValue value)
{
bool rVal = false;
_lockDictionary.PerformUsingWriteLock(() =>
{
// 如果不存在，则添加它
if (!_mDictionary.ContainsKey(key))
{
// 添加该值并设置标志
_mDictionary.Add(key, value);
rVal = true;
}
});
return rVal;
}
///
/// 如果键不存在，则添加值列表。
///
/// 要检查的键，添加
/// 如果键不存在，则添加的值
public void AddIfNotExists(IEnumerable keys, TValue defaultValue)
{
_lockDictionary.PerformUsingWriteLock(() =>
{
foreach (TKey key in keys)
{
// 如果不存在，则添加它
if (!_mDictionary.ContainsKey(key))
_mDictionary.Add(key, defaultValue);
}
});
}
// 添加如果不存在
///
/// 如果值不存在，则添加该值。返回值如果值已添加，则返回true。如果键已经存在，则其值将更新并返回false。
///
/// 检查的关键，添加
/// 如果键不存在，则添加的值
public bool AddIfNotExistsElseUpdate(TKey key, TValue value)
{
var rVal = false;
_lockDictionary.PerformUsingWriteLock(() =>
{
// 如果不存在，则添加它
if (!_mDictionary.ContainsKey(key))
{
// 添加该值并设置标志
_mDictionary.Add(key, value);
rVal = true;
}
else
_mDictionary[key] = value;
});
return rVal;
}
///
/// 如果键存在，则更新键的值。 如果更新，则返回true
///
///
///
public bool UpdateValueIfKeyExists(TKey key, TValue newValue)
{
bool rVal = false;
_lockDictionary.PerformUsingWriteLock(() =>
{
// 如果我们有密钥，然后更新它
if (!_mDictionary.ContainsKey(key)) return;
_mDictionary[key] = newValue;
rVal = true;
});
return rVal;
}
///
/// 如果键值对存在于字典中，则返回true
///
/// 键值对查找
public bool Contains(KeyValuePair item)
{
return _lockDictionary.PerformUsingReadLock(() => ((_mDictionary.ContainsKey(item.Key)) &&
(_mDictionary.ContainsValue(item.Value))));
}
///
/// 如果键存在于字典中，则返回true
///
/// 在字典中找到的关键
public bool ContainsKey(TKey key)
{
return _lockDictionary.PerformUsingReadLock(() => _mDictionary.ContainsKey(key));
}
///
/// 如果字典包含此值，则返回true
///
/// 找到的值
public bool ContainsValue(TValue value)
{
return _lockDictionary.PerformUsingReadLock(() => _mDictionary.ContainsValue(value));
}
///
/// 将键作为集合返回
///
public ICollection Keys
{
get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.Keys); }
}
///
/// 删除具有此键名称的元素
///
/// 删除的关键
public bool Remove(TKey key)
{
return _lockDictionary.PerformUsingWriteLock(() => (!_mDictionary.ContainsKey(key)) || _mDictionary.Remove(key));
}
///
/// 删除具有此键名称和值的元素。 返回如果项目已删除，则为true。
///
/// 删除的键
public bool Remove(KeyValuePair item)
{
return _lockDictionary.PerformUsingWriteLock(() =>
{
// 如果键不存在则跳过
TValue tempVal;
if (!_mDictionary.TryGetValue(item.Key, out tempVal))
return false;
//如果值不匹配，请跳过
return tempVal.Equals(item.Value) && _mDictionary.Remove(item.Key);
});
}
///
/// 从字典中删除与模式匹配的项。返回true成功
///
/// 基于键的可选表达式
/// 基于值的选项表达式
public bool Remove(Predicate predKey, Predicate predValue)
{
return _lockDictionary.PerformUsingWriteLock(() =>
{
// 如果没有键退出
if (_mDictionary.Keys.Count == 0)
return true;
//保存要删除的项目列表
var deleteList = new List();
// 过程密钥
foreach (var key in _mDictionary.Keys)
{
var isMatch = false;
//如果项匹配谓词，则将该项添加到列表中
if (predKey != null)
isMatch = (predKey(key));
// 如果此项目的值匹配，请添加它
if ((!isMatch) && (predValue != null) && (predValue(_mDictionary[key])))
isMatch = true;
// 如果我们有匹配，添加到列表
if (isMatch)
deleteList.Add(key);
}
// 从列表中删除所有项目
foreach (var item in deleteList)
_mDictionary.Remove(item);
return true;
});
}
///
/// 尝试返回在元素中找到的值 如果未找到任何值，则返回false
///
/// 找到的关键
/// 如果找到该键，则返回值
public bool TryGetValue(TKey key, out TValue value)
{
_lockDictionary.EnterReadLock();
try
{
return _mDictionary.TryGetValue(key, out value);
}
finally
{
_lockDictionary.ExitReadLock();
}
}
// 尝试获取值
///
///返回字典中值的集合
///
public ICollection Values
{
get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.Values); }
}
///
/// 值
///
///
///
public TValue this[TKey key]
{
get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary[key]); }
set { _lockDictionary.PerformUsingWriteLock(() => _mDictionary[key] = value); }
}
///
/// 清除字典
///
public void Clear()
{
_lockDictionary.PerformUsingWriteLock(() => _mDictionary.Clear());
}
///
/// 将字典的项目复制到键值对数组
///
/// 将键值对集合复制到
/// 开始复制的索引
public void CopyTo(KeyValuePair[] array, int arrayIndex)
{
_lockDictionary.PerformUsingReadLock(() => _mDictionary.ToArray().CopyTo(array, arrayIndex));
}
///
/// 返回字典中的项目数
///
public int Count
{
get { return _lockDictionary.PerformUsingReadLock(() => _mDictionary.Count); }
}
///
///始终返回false
///
public bool IsReadOnly
{
get { return false; }
}
///
/// 枚举器
///
///
public IEnumerator> GetEnumerator()
{
Dictionary localDict = null;
_lockDictionary.PerformUsingReadLock(() => localDict = new Dictionary(_mDictionary));
// 获取枚举器
return ((IEnumerable>)localDict).GetEnumerator();
}
///
///获取枚举器
///
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
Dictionary localDict = null;
_lockDictionary.PerformUsingReadLock(() => localDict = new Dictionary(_mDictionary));
return localDict.GetEnumerator();
}
}
以上创建安全的字典方法中，主要对字典的一些方法和属性进行重写操作，对某些方法进行锁设置。
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