StringEnumerator 类

定义

支持对 StringCollection 执行简单迭代。Supports a simple iteration over a StringCollection.

public ref class StringEnumerator
public class StringEnumerator
type StringEnumerator = class
Public Class StringEnumerator
继承
StringEnumerator

示例

下面的代码示例演示了的多个属性和方法 StringEnumeratorThe following code example demonstrates several of the properties and methods of StringEnumerator.

#using <System.dll>

using namespace System;
using namespace System::Collections::Specialized;
int main()
{
   
   // Creates and initializes a StringCollection.
   StringCollection^ myCol = gcnew StringCollection;
   array<String^>^myArr = {"red","orange","yellow","green","blue","indigo","violet"};
   myCol->AddRange( myArr );
   
   // Enumerates the elements in the StringCollection.
   StringEnumerator^ myEnumerator = myCol->GetEnumerator();
   while ( myEnumerator->MoveNext() )
      Console::WriteLine( "{0}", myEnumerator->Current );

   Console::WriteLine();
   
   // Resets the enumerator and displays the first element again.
   myEnumerator->Reset();
   if ( myEnumerator->MoveNext() )
      Console::WriteLine( "The first element is {0}.", myEnumerator->Current );
}

/*
This code produces the following output.

red
orange
yellow
green
blue
indigo
violet

The first element is red.

*/
using System;
using System.Collections.Specialized;

public class SamplesStringEnumerator  {

   public static void Main()  {

      // Creates and initializes a StringCollection.
      StringCollection myCol = new StringCollection();
      String[] myArr = new String[] { "red", "orange", "yellow", "green", "blue", "indigo", "violet" };
      myCol.AddRange( myArr );

      // Enumerates the elements in the StringCollection.
      StringEnumerator myEnumerator = myCol.GetEnumerator();
      while ( myEnumerator.MoveNext() )
         Console.WriteLine( "{0}", myEnumerator.Current );
      Console.WriteLine();

      // Resets the enumerator and displays the first element again.
      myEnumerator.Reset();
      if ( myEnumerator.MoveNext() )
         Console.WriteLine( "The first element is {0}.", myEnumerator.Current );
   }
}

/*
This code produces the following output.

red
orange
yellow
green
blue
indigo
violet

The first element is red.

*/
Imports System.Collections.Specialized

Public Class SamplesStringEnumerator

   Public Shared Sub Main()

      ' Creates and initializes a StringCollection.
      Dim myCol As New StringCollection()
      Dim myArr() As [String] = {"red", "orange", "yellow", "green", "blue", "indigo", "violet"}
      myCol.AddRange(myArr)

      ' Enumerates the elements in the StringCollection.
      Dim myEnumerator As StringEnumerator = myCol.GetEnumerator()
      While myEnumerator.MoveNext()
         Console.WriteLine("{0}", myEnumerator.Current)
      End While
      Console.WriteLine()

      ' Resets the enumerator and displays the first element again.
      myEnumerator.Reset()
      If myEnumerator.MoveNext() Then
         Console.WriteLine("The first element is {0}.", myEnumerator.Current)
      End If 

   End Sub

End Class


'This code produces the following output.
'
'red
'orange
'yellow
'green
'blue
'indigo
'violet
'
'The first element is red.

注解

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,调用会 Current 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,对的后续调用 MoveNext 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 ,则调用会 Current 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),则枚举器将失效且不可恢复,并且对或的下一个调用将 MoveNext Reset 引发 InvalidOperationExceptionIf changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException. 如果在和之间修改集合 MoveNext Current ,则 Current 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.

枚举数没有对集合的独占访问权;因此,从头到尾对一个集合进行枚举在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.

属性

Current

获取集合中的当前元素。Gets the current element in the collection.

方法

Equals(Object)

确定指定对象是否等于当前对象。Determines whether the specified object is equal to the current object.

(继承自 Object)
GetHashCode()

作为默认哈希函数。Serves as the default hash function.

(继承自 Object)
GetType()

获取当前实例的 TypeGets the Type of the current instance.

(继承自 Object)
MemberwiseClone()

创建当前 Object 的浅表副本。Creates a shallow copy of the current Object.

(继承自 Object)
MoveNext()

将枚举数推进到集合的下一个元素。Advances the enumerator to the next element of the collection.

Reset()

将枚举数设置为其初始位置,该位置位于集合中第一个元素之前。Sets the enumerator to its initial position, which is before the first element in the collection.

ToString()

返回表示当前对象的字符串。Returns a string that represents the current object.

(继承自 Object)

适用于

线程安全性

Shared此类型的公共静态(在 Visual Basic)成员是线程安全的。Public static (Shared in Visual Basic) members of this type are thread safe. 但不保证所有实例成员都是线程安全的。Any instance members are not guaranteed to be thread safe.

枚举整个集合本质上不是一个线程安全的过程。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.

另请参阅