C# 0 The Complete Reference

Obtaining an Array from an ArrayList 

When working with 

ArrayList

, you will sometimes want 

to obtain an actual array that contains the contents of the list. You can do this by calling 

ToArray( )

. There are several reasons why you might want to convert a collection into an 

array. Here are two: You may want to obtain faster processing times for certain operations, 

or you might need to pass an array to a method that is not overloaded to accept a collection. 

Whatever the reason, converting an 

ArrayList

 to an array is a trivial matter, as the following 

program shows:

// Convert an ArrayList into an array.

using System;

using System.Collections;

class ArrayListToArray {

  static void Main() {

    ArrayList al = new ArrayList();

    // Add elements to the array list.

    al.Add(1);

    al.Add(2);

    al.Add(3);

    al.Add(4);

    Console.Write("Contents: ");

    foreach(int i in al)

      Console.Write(i + " ");

    Console.WriteLine();

    // Get the array.

    int[] ia = (int[]) al.ToArray(typeof(int));

    int sum = 0;

    // Sum the array.

    for(int i=0; i

      sum += ia[i];

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    Console.WriteLine("Sum is: " + sum);

  }

}

The output from the program is shown here:

Contents: 1 2 3 4

Sum is: 10

The program begins by creating a collection of integers. Next,