C# Array.CreateInstance Method

You want to create an array that has elements of a certain type, which may not be known at compile-time, and also of a certain size. Using the Array.CreateInstance factory method, you can create arrays using a Type reference and some integers for the size.

Example

This program is divided into two sections: in the first section, we create a single-dimensional array of integers; in the second, we create a two-dimensional array. To call Array.CreateInstance, you must pass a Type pointer as the first argument; you could pass a variable reference of type Type instead of the typeof() operator result. To create a one-dimensional array, only pass one integer after the type; to create a two-dimensional array, pass two integers.

This C# example program uses the Array.CreateInstance method.

Program that uses Array.CreateInstance method [C#]

using System;

class Program
{
    static void Main()
    {
	// [1] Create a one-dimensional array of integers.
	{
	    Array array = Array.CreateInstance(typeof(int), 10);
	    int[] values = (int[])array;
	    Console.WriteLine(values.Length);
	}
	// [2] Create a two-dimensional array of bools.
	{
	    Array array = Array.CreateInstance(typeof(bool), 10, 2);
	    bool[,] values = (bool[,])array;
	    values[0, 0] = true;
	    Console.WriteLine(values.GetLength(0));
	    Console.WriteLine(values.GetLength(1));
	}
    }
}

Output

10
10
2

Why?

So why would you want to ever use the Array.CreateInstance method? Perhaps your program does not know the type of elements you want to create an array of at compile-time. You could pass any Type reference to the Array.CreateInstance; this does not need to be statically determined by the C# compiler. With newer versions of the C# language, generic types have alleviated this requirement.

Summary

The Array.CreateInstance method provides a way to construct arrays in memory using parameters. You do not need to know at compile-time what type of array will be created. As a factory method, the Array.CreateInstance returns the abstract base class Array; you can cast this to a specific type of array.