ListDictionary Class in C#

The ListDictionary class in C# implements the IDictionary interface using a singly linked list. It is optimized for small collections and is recommended for collections that typically contain fewer than 10 items. For larger collections, it's better to use Hashtable or Dictionary<TKey, TValue> for better performance.

Syntax

Following is the syntax for creating a ListDictionary −

ListDictionary dict = new ListDictionary();
dict.Add(key, value);

Key Properties

Common Methods

Using ListDictionary Properties

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      ListDictionary dict1 = new ListDictionary();
      dict1.Add("A", "Books");
      dict1.Add("B", "Electronics");
      dict1.Add("C", "Smart Wearables");
      dict1.Add("D", "Pet Supplies");
      dict1.Add("E", "Clothing");
      dict1.Add("F", "Footwear");
      
      Console.WriteLine("ListDictionary1 elements...");
      foreach(DictionaryEntry d in dict1) {
         Console.WriteLine(d.Key + " " + d.Value);
      }
      
      Console.WriteLine("Is the ListDictionary1 having fixed size? = " + dict1.IsFixedSize);
      Console.WriteLine("If ListDictionary1 read-only? = " + dict1.IsReadOnly);
      Console.WriteLine("Is ListDictionary1 synchronized = " + dict1.IsSynchronized);
      Console.WriteLine("The ListDictionary1 has the key M? = " + dict1.Contains("M"));
      
      ListDictionary dict2 = new ListDictionary();
      dict2.Add("1", "One");
      dict2.Add("2", "Two");
      dict2.Add("3", "Three");
      dict2.Add("4", "Four");
      dict2.Add("5", "Five");
      dict2.Add("6", "Six");
      
      Console.WriteLine("\nListDictionary2 key-value pairs...");
      IDictionaryEnumerator demoEnum = dict2.GetEnumerator();
      while (demoEnum.MoveNext())
         Console.WriteLine("Key = " + demoEnum.Key + ", Value = " + demoEnum.Value);
      
      Console.WriteLine("Is the ListDictionary2 having fixed size? = " + dict2.IsFixedSize);
      Console.WriteLine("If ListDictionary2 read-only? = " + dict2.IsReadOnly);
      Console.WriteLine("Is ListDictionary2 synchronized = " + dict2.IsSynchronized);
      Console.WriteLine("The ListDictionary2 has the key 5? = " + dict2.Contains("5"));
   }
}

The output of the above code is −

ListDictionary1 elements...
A Books
B Electronics
C Smart Wearables
D Pet Supplies
E Clothing
F Footwear
Is the ListDictionary1 having fixed size? = False
If ListDictionary1 read-only? = False
Is ListDictionary1 synchronized = False
The ListDictionary1 has the key M? = False

ListDictionary2 key-value pairs...
Key = 1, Value = One
Key = 2, Value = Two
Key = 3, Value = Three
Key = 4, Value = Four
Key = 5, Value = Five
Key = 6, Value = Six
Is the ListDictionary2 having fixed size? = False
If ListDictionary2 read-only? = False
Is ListDictionary2 synchronized = False
The ListDictionary2 has the key 5? = True

Comparing ListDictionary Objects

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      ListDictionary dict1 = new ListDictionary();
      dict1.Add("A", "Books");
      dict1.Add("B", "Electronics");
      dict1.Add("C", "Smart Wearables");
      dict1.Add("D", "Pet Supplies");
      dict1.Add("E", "Clothing");
      dict1.Add("F", "Footwear");
      
      Console.WriteLine("ListDictionary1 elements...");
      foreach(DictionaryEntry d in dict1) {
         Console.WriteLine(d.Key + " " + d.Value);
      }
      
      ListDictionary dict2 = new ListDictionary();
      dict2.Add("1", "One");
      dict2.Add("2", "Two");
      dict2.Add("3", "Three");
      dict2.Add("4", "Four");
      dict2.Add("5", "Five");
      dict2.Add("6", "Six");
      
      Console.WriteLine("\nListDictionary2 elements...");
      foreach(DictionaryEntry d in dict2) {
         Console.WriteLine(d.Key + " " + d.Value);
      }
      
      ListDictionary dict3 = new ListDictionary();
      dict3 = dict2;
      Console.WriteLine("\nIs ListDictionary3 equal to ListDictionary2? = " + (dict3.Equals(dict2)));
   }
}

The output of the above code is −

ListDictionary1 elements...
A Books
B Electronics
C Smart Wearables
D Pet Supplies
E Clothing
F Footwear

ListDictionary2 elements...
1 One
2 Two
3 Three
4 Four
5 Five
6 Six

Is ListDictionary3 equal to ListDictionary2? = True

Performance Characteristics

Conclusion

ListDictionary is ideal for small collections (under 10 items) due to its simple linked list structure. While it has O(n) lookup time, its low overhead makes it efficient for small datasets. For larger collections, consider using Dictionary<TKey, TValue> or Hashtable which provide O(1) average lookup performance.