Remove all entries from the ListDictionary in C#

The ListDictionary class in C# provides the Clear() method to remove all key-value pairs from the collection. This method is useful when you need to empty the entire dictionary without creating a new instance.

Syntax

Following is the syntax for the Clear() method −

listDictionary.Clear();

Parameters

The Clear() method takes no parameters.

Return Value

The method returns void and modifies the existing ListDictionary by removing all entries.

Using Clear() Method

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);
        }
        
        Console.WriteLine("Count of key/value pairs in Dictionary 2 = " + dict2.Count);
        
        ListDictionary dict3 = new ListDictionary();
        dict3 = dict2;
        Console.WriteLine("\nIs ListDictionary3 equal to ListDictionary2? = " + (dict3.Equals(dict2)));
        
        dict3.Clear();
        Console.WriteLine("Count of key/value pairs in Dictionary 3 = " + dict3.Count);
    }
}

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
Count of key/value pairs in Dictionary 2 = 6

Is ListDictionary3 equal to ListDictionary2? = True
Count of key/value pairs in Dictionary 3 = 0

Demonstrating Before and After Clear()

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 before Clear()...");
        foreach(DictionaryEntry d in dict1) {
            Console.WriteLine(d.Key + " " + d.Value);
        }
        Console.WriteLine("Count before Clear() = " + dict1.Count);
        
        dict1.Clear();
        
        Console.WriteLine("\nListDictionary1 elements after Clear()...");
        foreach(DictionaryEntry d in dict1) {
            Console.WriteLine(d.Key + " " + d.Value);
        }
        Console.WriteLine("Count after Clear() = " + dict1.Count);
    }
}

The output of the above code is −

ListDictionary1 elements before Clear()...
A Books
B Electronics
C Smart Wearables
D Pet Supplies
E Clothing
F Footwear
Count before Clear() = 6

ListDictionary1 elements after Clear()...
Count after Clear() = 0

Conclusion

The Clear() method provides an efficient way to remove all entries from a ListDictionary. After calling this method, the Count property becomes 0, and iterating through the dictionary produces no elements, effectively resetting the collection to an empty state.