Convert ArrayList, Array

In VB.NET an ArrayList can be converted to an array. This is possible with the ToArray Function. With it we get an Object array from an ArrayList.

ToArray is useful—it is not the same as the ToArray extension from System.Linq. We can perform the conversion with just one line of code.

Example

To start, we create an ArrayList. All the elements in the ArrayList are of type String. This is important—when we call ToArray, we get an Object array, not a String array.

Module Module1
    Sub Main()
        ' Create ArrayList.
        Dim list As ArrayList = New ArrayList()
        list.Add("Dot")
        list.Add("Net")
        list.Add("Perls")

        ' Get array of objects.
        Dim array() As Object = list.ToArray()

        For Each element In array
            ' Cast object to string.
            Dim value As String = element
            Console.WriteLine(value)
        Next
    End Sub
End Module
Dot
Net
Perls
Unhandled Exception: System.InvalidCastException: Unable to cast object of type 'System.Object[]'
to type 'System.String[]'.

Discussion

The ArrayList makes converting your collection to an array more difficult. If you use the List type, you can convert to a typed array such as String(). This results in clearer code.

We used the ToArray function on the ArrayList type to convert an ArrayList to an Object() array. We looked at the exception that is thrown when you try to cast the result array.