Array.Resize

A VB.NET array can be resized. This will either remove elements at the end if you resize it to be smaller, or add elements at the end if you resize it to be bigger.

Resize notes

The Resize method logically allocates a new array, and then copies to it. You can use Array.Resize to develop your own resizable collections.

Shrink example

To begin, we use Array.Resize on a 4-element integer array. We reduce (shrink) the size to 2 elements. The last 2 elements are erased.

Module Module1
    Sub Main()
        ' Create an array.
        Dim arr(3) As Integer
        arr(0) = 10
        arr(1) = 20
        arr(2) = 30
        arr(3) = 40

        ' Call Array.Resize to shrink the array.
        Array.Resize(arr, 2)

        ' Display.
        For Each value As Integer In arr
            Console.WriteLine(value)
        Next
    End Sub
End Module
10
20

Grow example

This program first declares an array of integers with 3 elements. Then, it displays the elements and also the array's total length.

Module Module1
    Sub Main()
        ' Create array of three elements.
        Dim arr(2) As Integer
        arr(0) = 1
        arr(1) = 2
        arr(2) = 3

        ' Display all elements and the length.
        For Each value As Integer In arr
            Console.Write(value)
            Console.Write(" ")
        Next
        Console.Write("- ")
        Console.WriteLine(arr.Length)

        ' Call Array.Resize.
        Array.Resize(arr, 6)

        ' Display all elements and the length.
        For Each value As Integer In arr
            Console.Write(value)
            Console.Write(" ")
        Next
        Console.Write("- ")
        Console.WriteLine(arr.Length)
    End Sub
End Module
1 2 3 - 3
1 2 3 0 0 0 - 6

Zero elements

Why are the elements zero? The default value of an integer on the heap is the value zero. All the bits are set to zeros.

Summary

Array.Resize() is used in many collections. When a collection such as a List or Dictionary needs to become larger, it calls Array.Resize to resize its internal buffers, which are arrays.