VB.NET ArrayList

ArrayList

An ArrayList is a dynamic array. It resizes to fit new elements. An array type offers superior performance. But the ArrayList is sized automatically by built-in code. It provides many helpful Functions for a linear collection.

Array

Add

First, the Add subroutine on the VB.NET ArrayList instance type is commonly used. The Add subroutine appends the object argument to the end of the internal ArrayList data structure. This program adds three elements to the ArrayList.

Tip:You do not need to check to see if there is room before adding the element.

Tip 2:There will always be room except in extreme circumstances such as out-of-memory situations.

Program that uses Add, ArrayList: VB.NET

Module Module1

    Sub Main()
	' Create a new ArrayList.
	' ... Then add three strings to it.
	Dim list As New ArrayList
	list.Add("One")
	list.Add("Two")
	list.Add("Three")
    End Sub

End Module

Parameter

Sub keyword

It is possible and often useful to receive an ArrayList type as a parameter to a Sub. This enables you to exploit structured programming with the ArrayList type to a larger extent.

Tip:The Example method here could be used with any ArrayList instance, with any elements in its internal storage.

Program that uses ArrayList with method: VB.NET

Module Module1

    Sub Main()
	' Create an ArrayList and add two elements to it.
	Dim list As New ArrayList
	list.Add(5)
	list.Add(7)
	' Use ArrayList as an argument to the method.
	Example(list)
    End Sub

    ''' <summary>
    ''' Receives ArrayList as argument.
    ''' </summary>
    Private Sub Example(ByVal list As ArrayList)
	Dim num As Integer
	For Each num In list
	    Console.WriteLine(num)
	Next
    End Sub

End Module

Output

5
7

AddRange

Dots: colored circles

It is possible to add a range of elements from one ArrayList onto the end of another ArrayList. To do this, please consider using the AddRange Sub. AddRange receives one argument—an ArrayList that contains elements you want to add.

Here:In this example, the two array lists are effectively concatenated. This is done with the AddRange Sub.

Program that uses AddRange method: VB.NET

Module Module1

    Sub Main()
	' Create an ArrayList and add two elements.
	Dim list1 As New ArrayList
	list1.Add(5)
	list1.Add(7)
	' Create a separate ArrayList.
	Dim list2 As New ArrayList
	list2.Add(10)
	list2.Add(13)
	' Add this ArrayList to the other one.
	list1.AddRange(list2)
	' Loop over the elements.
	Dim num As Integer
	For Each num In list1
	    Console.WriteLine(num)
	Next
    End Sub

End Module

Output

5
7
10
13

Count, Clear

Chaos

Often with ArrayList, you will not be sure how many elements are in the current instance. Fortunately, the ArrayList offers the Count instance property. This property quickly returns the number of elements in the ArrayList.

Property

Also:This example uses the Clear method. After you call the Clear method, the Count property will return zero elements.

Program that uses ArrayList and Count property: VB.NET

Module Module1

    Sub Main()
	' Add two elements to the ArrayList.
	Dim list As New ArrayList
	list.Add(9)
	list.Add(10)
	' Write the Count.
	Console.WriteLine(list.Count)
	' Clear the ArrayList.
	list.Clear()
	' Write the Count again.
	Console.WriteLine(list.Count)
    End Sub

End Module

Output

2
0

Insert, remove

Insert method

We show how to use the Add, RemoveAt, Insert, and RemoveRange methods on the ArrayList type in the VB.NET programming language. We have already seen the Add method in the first example.

Next:We see how the RemoveAt method works. It receives an index argument, which corresponds to the element index you want to remove.

The Insert method receives two arguments: the position you want to insert at, and the object reference itself. Finally, RemoveRange receives the index you want to start removing at, and the number of elements you want to remove.

Program that uses Add, RemoveAt, Insert, RemoveRange: VB.NET

Module Module1

    Sub Main()
	' Create an ArrayList and add three strings to it.
	Dim list As New ArrayList
	list.Add("Dot")
	list.Add("Net")
	list.Add("Perls")
	' Remove a string.
	list.RemoveAt(1)
	' Insert a string.
	list.Insert(0, "Carrot")
	' Remove a range.
	list.RemoveRange(0, 2)
	' Display.
	Dim str As String
	For Each str In list
	    Console.WriteLine(str)
	Next
    End Sub

End Module

Output

Perls

TryCast

Try keyword

In the ArrayList type, elements are not stored with a type directly. Instead they are accessed through the object base type. To cast an object to the more derived type you want to use, please use the TryCast operator.

The syntax for this operator receives two arguments: the element you want to cast from the ArrayList, and then the type to which you want to cast. The TryCast operator will not throw exceptions, as it uses the tester-doer pattern.

Program that uses ArrayList and TryCast: VB.NET

Module Module1

    Sub Main()
	' Create a new ArrayList.
	Dim list As New ArrayList
	list.Add("man")
	list.Add("woman")
	list.Add("plant")
	' Loop over the ArrayList with a For-loop.
	Dim i As Integer
	For i = 0 To list.Count - 1
	    ' Cast to a string.
	    Dim str As String = TryCast(list.Item(i), String)
	    Console.WriteLine(str)
	Next i
    End Sub

End Module

Output

man
woman
plant

GetRange

Steps

In this example, we look at how you can programmatically extract one part of an ArrayList instance into another ArrayList instance. To do this, please use the GetRange instance method on the original ArrayList instance.

Then, assign the result of the GetRange method call to a new ArrayList variable reference. GetRange receives the starting index from which you want to copy, and then the count of elements you want to get.

Integer
Program that uses ArrayList and GetRange: VB.NET

Module Module1

    Sub Main()
	' Create new ArrayList.
	Dim list1 As New ArrayList
	list1.Add("fish")
	list1.Add("amphibian")
	list1.Add("bird")
	list1.Add("plant")
	' Create a new ArrayList and fill it with the range from the first one.
	Dim list2 As New ArrayList
	list2 = list1.GetRange(2, 2)
	' Loop over the elements.
	Dim str As String
	For Each str In list2
	    Console.WriteLine(str)
	Next
    End Sub

End Module

Output

bird
plant

Summary

The VB.NET programming language

We examined the ArrayList type as used in the VB.NET programming language. The ArrayList type is a core class in the .NET Framework. Its usage in VB.NET is nuanced due to the casting syntax in this high-level language.

Review:This article does not cover all aspects of the ArrayList. It provides a tutorial for many common operations.


VB.NET: Collections