4.GetEnumerator()：返回循环访问 Dictionary<TKey, TValue> 的枚举器。
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;
}
}
}
