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VB.NET ArrayList ExamplesUse the ArrayList type, a resizable array. Add, remove and get elements.
ArrayList. This 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.
List
Functions. 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.
Add example. First the Add subroutine is often used. It appends the object argument to the end of the internal ArrayList data structure. This program adds 3 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.
VB.NET program that uses Add, ArrayList
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. It 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.
Tip The Example method here could be used with any ArrayList instance, with any elements in its internal storage.
VB.NET program that uses ArrayList with method
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
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AddRange. 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.
Argument 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.
VB.NET program that uses AddRange method
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
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Count, Clear. Often with ArrayList, you will not be sure how many elements are in the current instance. Fortunately, the ArrayList offers the Count property.
Count This is a property. Count quickly returns the number of elements in the ArrayList.
Property
Clear This example uses the Clear method. After you call the Clear method, the Count property will return zero elements.
VB.NET program that uses ArrayList and Count property
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
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Insert, Remove. We show how to use the Add, RemoveAt, Insert, and RemoveRange methods. We have already seen the Add method in the first example.
RemoveAt We see how the RemoveAt method works. It receives an index argument, which corresponds to the element index you want to remove.
Insert The Insert method receives two arguments: the position you want to insert at, and the object reference itself.
RemoveRange Finally, RemoveRange receives the index you want to start removing at, and the number of elements you want to remove.
VB.NET program that uses Add, RemoveAt, Insert, RemoveRange
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
Perls
TryCast. In 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.
Operator TryCast receives two arguments: the element we want to cast from the ArrayList, and the type to which we want to cast.
Warning The TryCast operator will not throw exceptions, as it uses the tester-doer pattern.
VB.NET program that uses TryCast, ArrayList
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
man woman plant
GetRange. Here we extract one part of an ArrayList into another. To do this, please use the GetRange method on the original ArrayList instance.
Then Assign the result of the GetRange method call to a new ArrayList variable reference.
Note GetRange receives the starting index from which you want to copy, and then the count of elements you want to get.
Integer
VB.NET program that uses ArrayList and GetRange
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. Dim str As String For Each str In list2 Console.WriteLine(str) Next End Sub End Module
bird plant
Hashtable. The ArrayList is similar to the Hashtable. For newer generic collections we have the List and Dictionary types. These are often used together in programs.
Hashtable
A consideration. There is rarely a need to use ArrayList in modern programs. Instead the List is used. It is faster and has clearer syntax (once you get past the generic declarations).
A summary. We 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.
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