ArrayListThis VB.NET collection 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.
ArrayList has many functions that help manage a linear collection. We add objects, we remove and insert things, and we count the number of elements.
First the Add() subroutine is often used. It appends the object argument to the end of the internal ArrayList data structure. This program adds three elements to the ArrayList.
out-of-memory situations.Module Module1
Sub Main()
' Create a new ArrayList, and add 3 strings to it.
Dim list As New ArrayList
list.Add("One")
list.Add("Two")
list.Add("Three")
Console.WriteLine(list.Count)
End Sub
End Module3It is possible and often useful to receive an ArrayList as a parameter to a Sub. We can specify it as a parameter with "As ArrayList." The syntax is simple.
ArrayList instance, with any elements in its internal storage.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)
For Each num As Integer In list
Console.WriteLine(num)
Next
End Sub
End Module5
7AddRangeIt 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.AddRange Sub.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.
For Each num As Integer In list1
Console.WriteLine(num)
Next
End Sub
End Module5
7
10
13Count, ClearOften with ArrayList, you will not be sure how many elements are in the current instance. Fortunately, the ArrayList offers the Count property.
Count is a property. Count quickly returns the number of elements in the ArrayList.Count property will return zero elements.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 Module2
0Insert, RemoveWe show how to use the Add(), RemoveAt(), Insert(), and RemoveRange() methods. We have already seen the Add() method in the first example.
RemoveAt method works. It receives an index argument, which corresponds to the element index you want to remove.Insert method receives two arguments: the position you want to insert at, and the object reference itself.RemoveRange receives the index you want to start removing at, and the number of elements you want to remove.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.
For Each str As String In list
Console.WriteLine(str)
Next
End Sub
End ModulePerlsTryCastIn the ArrayList, elements are not directly stored with a type. Instead they are accessed through the Object base type. To cast an Object to a more derived type, use TryCast.
TryCast receives 2 arguments: the element we want to cast from the ArrayList, and the type to which we want to cast.TryCast operator will not throw exceptions, as it uses the tester-doer pattern.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.
For i As Integer = 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 Moduleman
woman
plantGetRangeHere we extract one part of an ArrayList into another. To do this, please use the GetRange method on the original ArrayList instance.
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.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.
' ... Fill it with the range from the first one.
Dim list2 As New ArrayList
list2 = list1.GetRange(2, 2)
' Loop over the elements.
For Each str As String In list2
Console.WriteLine(str)
Next
End Sub
End Modulebird
plantWe examined the ArrayList type—this is a core class in .NET. It is harder to use in VB.NET due to the casting syntax required, but older programs often need it.