Shared array

Sometimes we want data to belong to a Class instance—each instantiation has its own data. But in VB.NET, sometimes an array is best shared between many class instances.

By specify the Shared modifier on an array, we can reuse that array's data throughout all instances. We can read and modify this global data.

Example

This program introduces an Example class, and in the class we declare and initialize 2 Shared arrays. The first one (values) has Integers and the second has Strings.

Class Example
    Shared Dim values() = {10, 20, 30, 40, 50}

    Shared Dim colors() As String = {"blue", "yellow", "orange", "red"}

    Public Shared Sub AddValues()
        ' Modify the elements in the Shared integer array.
        For i = 0 To values.Length - 1
            values(i) += 1
        Next
    End Sub

    Public Shared Sub ReassignColors()
        ' Create new colors array.
        colors = {"tan", "magenta", "grey"}
    End Sub

    Public Shared Sub PrintAll()
        ' Write contents of arrays to console.
        For Each value in values
            Console.WriteLine(value)
        Next        
        For Each color in colors
            Console.WriteLine(color)
        Next
        Console.WriteLine("...")
    End Sub
End Class

Module Module1
    Sub Main()
        ' Step 1: print the contents of the shared arrays.
        Example.PrintAll()

        ' Step 2: modify the elements within a shared array.
        Example.AddValues()

        ' Step 3: reassign the colors array to a new array.
        Example.ReassignColors()

        ' Step 4: print all changed data.
        Example.PrintAll()
    End Sub
End Module
10
20
30
40
50
blue
yellow
orange
red
...
11
21
31
41
51
tan
magenta
grey
...

Shared arrays are an ideal way to store data that it used throughout many class instances. This can reduce memory usage, speed up class construction, and make programs simpler.