In C#, the ListDictionary class is the part of the System.Collections.Specialized namespace. It is a collection that stores key-value pairs. It is used in scenarios where the number of elements is relatively small and the order of insertion needs to be preserved.
- It uses a single LinkedList to store key-value pairs.
- It preserves insertion order.
- The key cannot be null, but values can be null.
- It is not suitable for large datasets due to performance limitations.
Example: This example demonstrates how to add elements to a ListDictionary and then display its elements.
C#
// C# program to add elements to a ListDictionary
using System;
using System.Collections.Specialized;
using System.Collections;
class Geeks
{
static void Main()
{
// Create a new ListDictionary
ListDictionary ld = new ListDictionary();
// Add key-value pairs to the ListDictionary
ld.Add("Geek1", 1);
ld.Add("Geek2", 2);
ld.Add("Geek3", 3);
// Display the elements in the ListDictionary
Console.WriteLine("Elements in the ListDictionary:");
foreach (DictionaryEntry i in ld)
{
Console.WriteLine($"{i.Key}: {i.Value}");
}
}
}
OutputElements in the ListDictionary:
Geek1: 1
Geek2: 2
Geek3: 3
Declarartion of ListDictionary
In C#, the declaration of Dictionary can be done as:
ListDictionary variableName = new ListDictionary();
Constructors
| Constructors | Description |
|---|
| ListDictionary() | Creates an empty ListDictionary using the default comparer. |
| ListDictionary(IComparer) | Creates an empty ListDictionary using the specified compare |
Example: This example demonstrates how to retrieve the count of pairs and displaying the key-value pair.
C#
// C# program to demonstrates the
// working of Count property
using System;
using System.Collections;
using System.Collections.Specialized;
class Geeks {
public static void Main()
{
// Creating a ListDictionary named ld
ListDictionary ld = new ListDictionary();
// Adding key/value pairs
ld.Add("Java", "1");
ld.Add("C++", "2");
ld.Add("Js", "3");
ld.Add("Python", "4");
// To get count of key-value pairs
Console.WriteLine("Total number of Key-value pairs: "
+ ld.Count);
// Displaying the key-value pairs
Console.WriteLine("Displaying the key-value pair: ");
foreach(DictionaryEntry i in ld)
{
Console.WriteLine("Key: "+i.Key + " , "+ "Value: "
+ i.Value);
}
}
}
OutputTotal number of Key-value pairs: 4
Displaying the key-value pair:
Key: Java , Value: 1
Key: C++ , Value: 2
Key: Js , Value: 3
Key: Python , Value: 4
Properties
| Properties | Description |
|---|
| Count | Gets the number of key/value pairs contained in the ListDictionary. |
| IsFixedSize | Gets a value indicating whether the ListDictionary has a fixed size. |
| IsReadOnly | Gets a value indicating whether the ListDictionary is read-only. |
| IsSynchronized | Gets a value indicating whether the ListDictionary is synchronized (thread safe). |
| Item[Object] | Gets or sets the value associated with the specified key. |
| Keys | Gets an ICollection containing the keys in the ListDictionary. |
| SyncRoot | Gets an object that can be used to synchronize access to the ListDictionary. |
| Values | Gets an ICollection containing the values in the ListDictionary. |
Example 1: This example demonstrates how to retrieve the count of pairs.
C#
// C# Program to get the number
// of key/value pairs contained
// in the ListDictionary
using System;
using System.Collections;
using System.Collections.Specialized;
class Geeks {
public static void Main()
{
// Creating a ListDictionary named ld
ListDictionary ld = new ListDictionary();
// Adding key/value pairs
ld.Add("100", "1");
ld.Add("200", "2");
ld.Add("300", "3");
ld.Add("400", "4");
// Displaying the number of key/value
// pairs contained in the ListDictionary
Console.WriteLine(ld.Count);
}
}
Example 2: This example checks if the dictionary is read-only.
C#
// C# program demonstrates the
// use of IsReadOnly properity
using System;
using System.Collections;
using System.Collections.Specialized;
class Geeks {
public static void Main() {
// Creating a ListDictionary named ld
ListDictionary ld = new ListDictionary();
// Adding key/value pairs in l
ld.Add("100", "1");
ld.Add("200", "2");
ld.Add("300", "3");
ld.Add("400", "4");
// Checking if ListDictionary is read-only
Console.WriteLine(ld.IsReadOnly);
}
}
Methods
| Methods | Description |
|---|
| Add(Object, Object) | Adds an entry with the specified key and value into the ListDictionary. |
| Clear() | Removes all entries from the ListDictionary. |
| Contains(Object) | Determines whether the ListDictionary contains a specific key. |
| CopyTo(Array, Int32) | Copies the ListDictionary entries to a one-dimensional Array instance at the specified index. |
| Equals(Object) | Determines whether the specified object is equal to the current object. |
| GetEnumerator() | Returns an IDictionaryEnumerator that iterates through the ListDictionary. |
| GetHashCode() | Serves as the default hash function. |
| GetType() | Gets the Type of the current instance. |
| MemberwiseClone() | Creates a shallow copy of the current Object. |
| Remove(Object) | Removes the entry with the specified key from the ListDictionary. |
| ToString() | Returns a string that represents the current object. |
Example: This example demonstrates how to remove all the entries using Clear() method.
C#
// C# Program to remove all entries
// from the ListDictionary
using System;
using System.Collections;
using System.Collections.Specialized;
class Geeks {
public static void Main()
{
// Creating a ListDictionary named ld
ListDictionary ld = new ListDictionary();
// Adding key/value pairs in l
ld.Add("I", "first");
ld.Add("II", "second");
// To get count of key/value pairs
Console.WriteLine("Total key-value pairs in ListDictionary are: "
+ ld.Count);
// Displaying the key/value pairs
Console.WriteLine("The key-value pairs in ListDictionary are: ");
foreach(DictionaryEntry i in ld)
{
Console.WriteLine(i.Key + " " + i.Value);
}
// Removing all entries from the ListDictionary
ld.Clear();
// To get count of key/value pairs
Console.WriteLine("Total key/value pairs in ListDictionary are: "
+ ld.Count);
}
}
OutputTotal key-value pairs in ListDictionary are: 2
The key-value pairs in ListDictionary are:
I first
II second
Total key/value pairs in ListDictionary are: 0
