Hashtable.GetEnumerator方法用于返回迭代Hashtable的IDictionaryEnumerator。
句法:
public virtual System.Collections.IDictionaryEnumerator GetEnumerator ();
返回值:它返回哈希表的IDictionaryEnumerator。
下面的程序说明了Hashtable.GetEnumerator方法的用法:
范例1:
// C# code to get an IDictionaryEnumerator
// that iterates through the Hashtable
using System;
using System.Collections;
class GFG {
// Driver code
public static void Main()
{
// Creating a Hashtable named myhash
Hashtable myhash = new Hashtable();
// Adding key/value pairs in myhash
myhash.Add("A", "Apple");
myhash.Add("B", "Banana");
myhash.Add("C", "Cat");
myhash.Add("D", "Dog");
myhash.Add("E", "Elephant");
myhash.Add("F", "Fish");
// To get an IDictionaryEnumerator
// for the Hashtable.
IDictionaryEnumerator myEnumerator = myhash.GetEnumerator();
// If MoveNext passes the end of the
// collection, the enumerator is positioned
// after the last element in the collection
// and MoveNext returns false.
while (myEnumerator.MoveNext())
Console.WriteLine(myEnumerator.Key + " --> "
+ myEnumerator.Value);
}
}
输出:
B --> Banana
C --> Cat
A --> Apple
F --> Fish
D --> Dog
E --> Elephant
范例2:
// C# code to get an IDictionaryEnumerator
// that iterates through the Hashtable
using System;
using System.Collections;
class GFG {
// Driver code
public static void Main()
{
// Creating a Hashtable named myhash
Hashtable myhash = new Hashtable();
// Adding key/value pairs in myhash
myhash.Add("I", "first");
myhash.Add("II", "second");
myhash.Add("III", "third");
myhash.Add("IV", "fourth");
myhash.Add("V", "fifth");
// To get an IDictionaryEnumerator
// for the Hashtable.
IDictionaryEnumerator myEnumerator = myhash.GetEnumerator();
// If MoveNext passes the end of the
// collection, the enumerator is positioned
// after the last element in the collection
// and MoveNext returns false.
while (myEnumerator.MoveNext())
Console.WriteLine(myEnumerator.Key + " --> "
+ myEnumerator.Value);
}
}
输出:
III --> third
IV --> fourth
V --> fifth
II --> second
I --> first
笔记:
- C#语言的foreach语句隐藏了枚举器的复杂性。因此,建议使用foreach,而不是直接操作枚举器。
- 枚举数可用于读取集合中的数据,但不能用于修改基础集合。
- 在调用MoveNext或Reset之前,Current返回相同的对象。 MoveNext将Current设置为下一个元素。
- 只要集合保持不变,枚举数将保持有效。如果对集合进行了更改(例如添加,修改或删除元素),则枚举数将无法恢复,并且其行为是不确定的。
- 此方法是O(1)操作。
参考:
- https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.hashtable.getenumerator?view=netframework-4.7.2