Hashtable.IEnumerable.GetEnumerator Hashtable.IEnumerable.GetEnumerator Hashtable.IEnumerable.GetEnumerator Method

定义

返回循环访问集合的枚举数。Returns an enumerator that iterates through a collection.

 virtual System::Collections::IEnumerator ^ System.Collections.IEnumerable.GetEnumerator() = System::Collections::IEnumerable::GetEnumerator;
System.Collections.IEnumerator IEnumerable.GetEnumerator ();
Function GetEnumerator () As IEnumerator Implements IEnumerable.GetEnumerator

返回

可用于循环访问集合的 IEnumeratorAn IEnumerator that can be used to iterate through the collection.

实现

注解

[Visual Basic, C#][Visual Basic, C#]

C# 语言的 foreach 语句(在 Visual Basic 中为 for each)隐藏了枚举数的复杂性。The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. 因此,建议使用 foreach,而不是直接操作枚举数。Therefore, using foreach is recommended, instead of directly manipulating the enumerator.

枚举器可用于读取集合中的数据,但不能用于修改基础集合。Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

最初,枚举数定位在集合中第一个元素的前面。Initially, the enumerator is positioned before the first element in the collection. Reset 也会将枚举器放回此位置。Reset also brings the enumerator back to this position. 在此位置, 调用Current会引发异常。At this position, calling Current throws an exception. 因此,在读取 MoveNext 的值之前,必须调用 Current 将枚举器向前移动到集合的第一个元素。Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

在调用 CurrentMoveNext 之前,Reset 返回同一对象。Current returns the same object until either MoveNext or Reset is called. MoveNextCurrent 设置为下一个元素。MoveNext sets Current to the next element.

如果MoveNext越过集合的末尾, 则枚举器将定位在集合中最后一个元素之后, 并MoveNext返回falseIf MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. 当枚举器位于此位置时, 对MoveNext的后续调用也将返回。 falseWhen the enumerator is at this position, subsequent calls to MoveNext also return false. 如果最后一次调用MoveNext返回false, 则Current调用会引发异常。If the last call to MoveNext returned false, calling Current throws an exception. 若要再次将 Current 设置为集合的第一个元素,可以调用 Reset 并接着调用 MoveNextTo set Current to the first element of the collection again, you can call Reset followed by MoveNext.

只要集合保持不变,枚举数就保持有效。An enumerator remains valid as long as the collection remains unchanged. 如果对集合所做的更改 (如添加、修改或删除元素), 则枚举器可以失效, 对MoveNextReset的下一个调用将引发InvalidOperationExceptionIf changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator can be invalidated and the next call to MoveNext or Reset throws an InvalidOperationException. 如果在和MoveNext Current之间修改集合, Current则将返回它设置为的元素, 即使枚举器已失效也是如此。If the collection is modified between MoveNext and Current, Current returns the element that it is set to, even if the enumerator is already invalidated.

该枚举数不具有独占访问集合的权限;因此,枚举整个集合本质上不是一个线程安全的过程。The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread safe procedure. 即使某个集合已同步,其他线程仍可以修改该集合,这会导致枚举数引发异常。Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 若要确保枚举过程中的线程安全性,可以在整个枚举期间锁定集合,或者捕获由其他线程进行的更改所导致的异常。To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

此方法为 O (1) 操作。This method is an O(1) operation.

适用于

另请参阅