The Hashtable collection in the C# language and .NET Framework provides a way to access objects based on a key quickly. But the Hashtable does not implement advanced logic for iterating over the contents. You can instead use the DictionaryEntry type in a foreach loop construct.
This example uses the Hashtable type and instantiates it upon the managed heap. Then, three key-value pairs are added to the instance. Third, we use the foreach-loop construct to loop over the contents of the Hashtable instance—this gives us a pair of values, encoded in a DictionaryEntry value. To access the key and value of a DictionaryEntry, please use the named properties.
This C# example program uses the DictionaryEntry struct with Hashtable.
Program that uses DictionaryEntry type and foreach [C#]
using System;
using System.Collections;
class Program
{
static void Main()
{
// Create hashtable with some keys and values.
Hashtable hashtable = new Hashtable();
hashtable.Add(1, "one");
hashtable.Add(2, "two");
hashtable.Add(3, "three");
// Enumerate the hashtable.
foreach (DictionaryEntry entry in hashtable)
{
Console.WriteLine("{0} = {1}", entry.Key, entry.Value);
}
}
}
Output
3 = three
2 = two
1 = one
The DictionaryEntry type is not actually tied to the Hashtable collection in any way. You can create an instance of the DictionaryEntry to store a key-value pair anywhere you want to. Because this type is a value type, it will be copied onto the evaluation stack whenever it is used as a local variable or method parameter. The DictionaryEntry stores two object pointers, which are four bytes on 32-bit operating systems but eight bytes on 64-bit operating systems.
To loop over a Hashtable collection, then, you can use a foreach-loop construct and then access the properties on each DictionaryEntry. As with many associative collections, the looping order is undefined. The DictionaryEntry type, as a value type, does not incur the overhead of objects; further, it can be instantiated anywhere in your program to store a pair of object references.
Collections