Remove all elements from the ArrayList in C#

To remove all elements from an ArrayList in C#, you can use the Clear() method. This method removes all elements from the ArrayList and sets the Count property to zero.

Syntax

Following is the syntax for the Clear() method −

arrayList.Clear();

Parameters

The Clear() method does not take any parameters.

Return Value

The Clear() method does not return any value. It is a void method that modifies the ArrayList in-place.

Using Clear() to Remove All Elements

The following example demonstrates how to use the Clear() method to remove all elements from an ArrayList −

using System;
using System.Collections;

public class Demo {
   public static void Main(string[] args) {
      ArrayList arrList = new ArrayList();
      arrList.Add("One");
      arrList.Add("Two");
      arrList.Add("Three");
      arrList.Add("Four");
      arrList.Add("Five");
      
      Console.WriteLine("Elements in ArrayList...");
      foreach (string res in arrList) {
         Console.WriteLine(res);
      }
      
      Console.WriteLine("Count of elements in ArrayList = " + arrList.Count);
      arrList.Clear();
      Console.WriteLine("Count of elements in ArrayList (After Clear) = " + arrList.Count);
   }
}

The output of the above code is −

Elements in ArrayList...
One
Two
Three
Four
Five
Count of elements in ArrayList = 5
Count of elements in ArrayList (After Clear) = 0

Clear() vs Reference Assignment

The following example shows the difference between Clear() method and reference assignment when multiple variables reference the same ArrayList −

using System;
using System.Collections;

public class Demo {
   public static void Main(string[] args) {
      ArrayList list1 = new ArrayList();
      list1.Add("A");
      list1.Add("B");
      list1.Add("C");
      
      ArrayList list2 = list1; // Both reference same ArrayList
      
      Console.WriteLine("Before Clear:");
      Console.WriteLine("List1 Count = " + list1.Count);
      Console.WriteLine("List2 Count = " + list2.Count);
      Console.WriteLine("Are they the same object? " + ReferenceEquals(list1, list2));
      
      list1.Clear(); // Clears the ArrayList that both variables reference
      
      Console.WriteLine("\nAfter Clear:");
      Console.WriteLine("List1 Count = " + list1.Count);
      Console.WriteLine("List2 Count = " + list2.Count);
   }
}

The output of the above code is −

Before Clear:
List1 Count = 3
List2 Count = 3
Are they the same object? True

After Clear:
List1 Count = 0
List2 Count = 0

Conclusion

The Clear() method is the most efficient way to remove all elements from an ArrayList in C#. It instantly removes all elements and resets the Count to zero, making it useful when you need to reuse an existing ArrayList without creating a new instance.