C# dictionary<TKey,TValue>加入键和值后数据类型怎么就变成了KeyValuePair<TKey, TValue>，代码是怎么实现的？

Question

例如 如下图，我键保存了个字符串"one" 值保存了个时间类型，存到字典里的类型怎么就成了KeyValuePair<string,object>了，字典里保存键跟值主要调用的是private void Insert(TKey key, TValue value, bool add)方法，但是在这个方法里没看到把键和值转成KeyValuePair，请问微软是怎么把键和值转成KeyValuePair的？

Answer 1

首先：不能直接用对象当成布尔类型用作if判断，应该是使用：

if(discusOne!=null)
{
  ……
}

其次：你的 Dictionary的Value类型应该是DateTime类型，不是object类型：

Dictionary<string,DateTime> dic1 = new Dictionary<string,DateTime>();

---

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Answer 2

首先：不能直接用对象当成布尔类型用作if判断，应该是使用：

if(discusOne!=null)
{
  ……
}

其次：你的 Dictionary的Value类型应该是DateTime类型，不是object类型：

Dictionary<string,DateTime> dic1 = new Dictionary<string,DateTime>();

---

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Answer 3

这是继承 IDictionary 接口的原因。

IEnumerator< T > 中返回了 KeyValuePair 。

                       current = new KeyValuePair<TKey, TValue>(dictionary.entries[index].key, dictionary.entries[index].value);

Answer 4

 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);

关键是dictionary<TKey,TValue>在哪里调用的这方法看不到

Answer 5

因为Enumerate 的时候是使用GetEnumerator函数，而且实现了 IEnumerable<KeyValuePair<TKey, TValue>> 接口

public Dictionary<TKey, TValue>.Enumerator GetEnumerator()
{
    return new Dictionary<TKey, TValue>.Enumerator(this, 2);
}

而Enumerator的定义是:

public struct Enumerator : IEnumerator<KeyValuePair<TKey, TValue>>, IDisposable, IDictionaryEnumerator, IEnumerator

 {
            internal const int DictEntry = 1;
            internal const int KeyValuePair = 2;
            private Dictionary<TKey, TValue> dictionary;
            private int version;
            private int index;
            private KeyValuePair<TKey, TValue> current;
            private int getEnumeratorRetType;
            /// <summary>Gets the element at the current position of the enumerator.</summary>
            /// <returns>The element in the <see cref="T:System.Collections.Generic.Dictionary`2" /> at the current position of the enumerator.</returns>
            [__DynamicallyInvokable]
            public KeyValuePair<TKey, TValue> Current
            {
                [__DynamicallyInvokable, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
                get
                {
                    return this.current;
                }
            }

.....

当调试器去取值的时候，是使用的Enumerate， 取到的数据类型就是KeyValuePair<TKey, TValue>了。

Answer 6

非常感谢   Simon YunZhi Cai，我认为你说的是正确的。