ArrayList: Dynamic array in .NET  by: juliet

ArrayList: Dynamic array in .NET

by:

This simple tutorial teaches you how to work with an ArrayList class. Many people who switches from the C/C++ world found that there is no dynamic memory allocation in the arrays of C#. Actually there is a class in .NET which allows you to do the same functionality as dynamic memory allocation but is much simpler to use - the ArrayList class. With ArrayList, you no longer need to worry about freeing up memory after allocation of memory and array bound overflow.

Here is the code to build an ArrayList, and retrieve content from it: using System;using System.Collections;

class TestArrayList { public static void Main() { ArrayList myList = new ArrayList(); int i; for(i=0; i<5; i++) myList.Add(i); myList.Add("Hello"); for(i=0; iConsole.WriteLine("Array Index [{0}]: {1}", i, myList[i].ToString()); }}

To use it, you must "using" the System.Collections namespace since the ArrayList class is defined in it. The Add() method of the ArrayList accept an Object instance as its argument, therefore, as you can see, you can put into it an integer or a string alike, or any user-defined class.

In the second for loop, you would see I had used the Count property of the ArrayList class to retrieve the number of element in it. It is very convenient since you do not have to book keep the number of element in this array. Finally, remember when you print the content of the ArrayList to the screen, you have to use the ToString() method of the element, since retrieval of an myList[i] element would return an Object type.

1 

VB.NET ArrayList ExamplesYou want to use the ArrayList type in the VB.NET programming language. Although an array type may offer superior performance, the ArrayList can be expanded automatically by built-in code, making a dynamic array. Here, we describe the ArrayList type in the VB.NET language, which is one of the easiest and more useful data types.

Using AddFirst, the Add method on the VB.NET ArrayList instance type is very commonly used. The Add method appends the object argument to the very end of the internal ArrayList data structure. You do not need to check to see if there is room before adding the element; there will always be room except in extreme circumstances such as out-of-memory situations. This program adds three elements to the ArrayList.

--- Program that uses ArrayList and Add (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

Using parameterHere, we describe how it is possible and often useful to receive an ArrayList type as a parameter to a method Sub. This enables you to exploit structured programming with the ArrayList type to a larger extent. 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 of the program ---

5

7

Using AddRangeIt 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 method. The AddRange method receives one argument, which is an ArrayList type that contains elements you want to add to the end of the instance ArrayList you call the method on. In this example, the two array lists are effectively concatenated.

--- 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 of the program ---

5

7

10

13

Using Count and ClearOften when programming with the ArrayList type, 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. Also, this example demonstrates the Clear method. After you call the Clear method, the Count property will return zero elements: this is because all of the elements were removed.

--- 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 of the program ---

2

0

Adding and removing elementsIn this section, we demonstrate how you can 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 in this article. 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, the RemoveRange methods receives two arguments: 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 of the program ---

Perls

Using TryCast

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 of the program ---

man

woman

plant

Using GetRangeIn 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. The GetRange uses the standard pattern for range-based methods: it receives the starting index from which you want to copy, and then the count of elements you want to get.

--- 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 of the program ---

bird

plant

Use array and ArrayList (VB.net)

<%@ Page Language="VB" %><script runat="server">    Dim ColorList(6) as String    Dim FontList as new ArrayList()        Sub Page_Load      ' Add the colors to the array      ColorList(0) = "Red"      ColorList(1) = "Orange"      ColorList(2) = "Yellow"      ColorList(3) = "Green"      ColorList(4) = "Blue"      ColorList(5) = "Indigo"      ColorList(6) = "Violet"          FontList.Add("Times New Roman")      FontList.Add("Arial")      FontList.Add("Verdana")      FontList.Add("Comic Sans MS")          If Not Page.IsPostback        Dim ColorName as String            For Each ColorName in ColorList          ddlColorList.Items.Add(ColorName)        Next            ddlFontList.DataSource = FontList        ddlFontList.DataBind()          End If    End Sub        Sub btnSelectColor_Click(sender As Object, e As EventArgs)      lblOutputMessage.Text = "You selected " & _        ddlColorList.SelectedItem.Value & " text written in " & _        ddlFontList.SelectedItem.Value      lblOutputMessage.ForeColor = _        System.Drawing.Color.FromName(ddlColorList.SelectedItem.Text)      lblOutputMessage.Font.Name = _        ddlFontList.SelectedItem.Text

        End Sub

</script><html><head></head><body>    <form runat="server">        <p>            Select a color from the list:<asp:DropDownList id="ddlColorList" runat="server"        </p>        <p>            Then select a font sytle from the list:             <asp:DropDownList id="ddlFontList" runat="server"></asp:DropDownList>        </p>        <p>            &nbsp;<asp:Button id="btnSelectColor" onclick="btnSelectColor_Click" runat=        </p>        <p>            <asp:Label id="lblOutputMessage" runat="server"></asp:Label>        </p>    </form></body></html>

           

ArrayList is one of the most flixible data structure from VB.NET Collections. ArrayList contains a simple list of values. Very easily we can add , insert , delete , view etc.. to do with ArrayList. It is very flexible becuse we can add without any size information , that is it grow dynamically and also shrink .

Important functions in ArrayListAdd : Add an Item in an ArrayList

Insert : Insert an Item in a specified position in an ArrayList

Remove : Remove an Item from ArrayList

RemoveAt: remeove an item from a specified position

Sort : Sort Items in an ArrayList

How to add an Item in an ArrayList ?

Syntax : ArrayList.add(Item)

Item : The Item to be add the ArrayList

Dim ItemList As New ArrayList()

ItemList.Add("Item4")

How to Insert an Item in an ArrayList ?

Syntax : ArrayList.insert(index,item)

index : The position of the item in an ArrayList

Item : The Item to be add the ArrayList

ItemList.Insert(3, "item6")

How to remove an item from arrayList ?

Syntax : ArrayList.Remove(item)

Item : The Item to be add the ArrayList

ItemList.Remove("item2")

How to remove an item in a specified position from an ArrayList ?

Syntax : ArrayList.RemoveAt(index)

index : the position of an item to remove from an ArrayList

ItemList.RemoveAt(2)

How to sort ArrayList ?

Syntax : ArrayListSort()

The following VB.NET source code shows some function in ArrayList

         VB.NET Source Code Download           Print Source Code

         How to VB.NET ArrayList - Download

         VB.Net Tutorial

Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles Button1.Click Dim i As Integer Dim ItemList As New ArrayList() ItemList.Add("Item4") ItemList.Add("Item5") ItemList.Add("Item2") ItemList.Add("Item1") ItemList.Add("Item3") MsgBox("Shows Added Items") For i = 0 To ItemList.Count - 1 MsgBox(ItemList.Item(i)) Next 'insert an item ItemList.Insert(3, "Item6") 'sort itemms in an arraylist ItemList.Sort()

'remove an item ItemList.Remove("Item1") 'remove item from a specified index ItemList.RemoveAt(3) MsgBox("Shows final Items the ArrayList") For i = 0 To ItemList.Count - 1 MsgBox(ItemList.Item(i)) Next End SubEnd Class

When you execute this program , at first add five items in the arraylist and displays. Then again one more item inserted in the third position , and then sort

all items. Next it remove the item1 and also remove the item in the third position . Finally it shows the existing items.

Work with VB.NET's ArrayList methods and properties

By Irina Medvinskaya, TechRepublic | 2006/10/16 10:46:02

Tags: .net, arraylist, vb

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The ability to use collections is important in any language and practical for any application. Collections allow you to manage groups of objects.

In this article, I'll look at how to use an ArrayList class, which provides basic functionality that is useful to most applications. I'll also cover the basics about the methods

within the class.

An ArrayList classAn ArrayList class represents a dynamically sized, index-based collection of objects. In the cases where you don't know the number of objects that you would store, an

ArrayList class is a good option to utilize.

The System.Collections.ArrayList class provides general collection functionality that is suitable for many uses. The class allows you to dynamically add and remove items

from a list. Items are accessed by using an index of the item.

The following example shows how to create a new instance of an ArrayListclass:

Dim arrayListInfo As New System.Collections.ArrayList()

The Add methodOnce instantiated, you can add items to an ArrayList class using the Add method. For example, the following code shows how to add items to an existing ArrayList class:

Dim arrayListInfo As New ArrayList()

ArrayListInfo.Add("Item1")

arrayListInfo.Add("Item2")

arrayListInfo.Add("Item3")

An ArrayList class is a zero-based collection; therefore, the first object added to the list is assigned the index zero, and all subsequent objects are assigned to the next

available index.

The Item property indexerThe Item property of an ArrayList class gets or sets the element at the specified index. You can retrieve an item from an ArrayList class at a particular index by using the

Item property.

This is the default property for collections in VB.NET. This means you can access it without using the Item property name, allowing syntax similar to that of an array.

The following example shows how to retrieve a reference to an object in a collection:

Dim objItem As Object

objItem = arrayListInfo(0)

or

Dim objItem As Object

objItem = arrayListInfo.Item(0)

The Remove and RemoveAt methodsIn order to remove an item from a collection, you can utilize either the Remove or RemoveAt method. The Remove method requires a reference to an object contained

within the collection as a parameter and removes that object from the collection. The RemoveAtmethod allows you to remove an object at a particular index.

As items are removed from a collection, the index numbers are reassigned to occupy any available spaces; so, index values are not static and might not always return the

same reference.

The Count property

The Count property returns the current number of items in a collection. The collections are always zero-based; therefore, the Count property will always return a value that is one

greater than the upper bound of the array.

Stack is one of another easy to use VB.NET Collections . Stack follows the push-pop operations. That is we can Push Items into Stack and Pop it later . And It follows the Last In First Out (LIFO) system. That is we can push the items into a stack and get it in reverse order. Stack returns the last item first.

Commonly used methods :Push : Add (Push) an item in the stack datastructure

Syntax : Stack.Push(Object)

Object : The item to be inserted.

Pop : Pop return the item last Item to insert in stack

Syntax : Stack.Pop()

Return : The last object in the Stack

Contains : Check the object contains in the stack

Syntax : Stack.Contains(Object)

Object : The specified Object to be seach

The following VB.NET Source code shows some of commonly used functions :

         VB.NET Source Code Download           Print Source Code

         How to VB.Net Stack - Download

         VB.Net Tutorial

Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles Button1.Click Dim stackTable As New Stack stackTable.Push("Sun") stackTable.Push("Mon") stackTable.Push("Tue") stackTable.Push("Wed") stackTable.Push("Thu") stackTable.Push("Fri") stackTable.Push("Sat") If stackTable.Contains("Wed") Then MsgBox(stackTable.Pop()) Else MsgBox("not exist") End If End SubEnd Class

When you execute this program add seven items in the stack . Then its checks the item "Wed" exist in the Stack. If the item exist in the Stack , it Pop the last item from Stack , else it shows the msg "Not Exist"

HashTable stores a Key Value pair type collection of data . We can retrive items from hashTable to provide the key . Both key and value are Objects.

The common functions using in Hashtable are :Add : To add a pair of value in HashTable

Syntax : HashTable.Add(Key,Value)

Key : The Key value

Value : The value of corrosponding key

ContainsKey : Check if a specified key exist or not

Synatx : HashTable.ContainsKey(key)

Key : The Key value for search in HahTable

ContainsValue : Check the specified Value exist in HashTable

Synatx : HashTable.ContainsValue(Value)

Value : Search the specified Value in HashTable

Remove : Remove the specified Key and corrosponding Value

Syntax : HashTable.Remove(Key)

Key : The argument key of deleting pairs

The following source code shows all important operations in a HashTable

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         How to VB.Net HashTable - Download

         VB.Net Tutorial

Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles Button1.Click Dim weeks As New Hashtable Dim day As DictionaryEntry weeks.Add("1", "Sun") weeks.Add("2", "Mon") weeks.Add("3", "Tue") weeks.Add("4", "Wed") weeks.Add("5", "Thu") weeks.Add("6", "Fri") weeks.Add("7", "Sat") 'Display a single Item MsgBox(weeks.Item("5")) 'Search an Item If weeks.ContainsValue("Tue") Then MsgBox("Find") Else MsgBox("Not find") End If 'remove an Item weeks.Remove("3") 'Display all key value pairs For Each day In weeks MsgBox(day.Key " -- " day.Value) Next End SubEnd Class

Arrays are using for store similar data types grouping as a single unit. We can access Array elements by its numeric index.

Dim week(6) As String

The above Vb.Net statements means that , an Array named as week declared as a String type and it can have the capability of seven String type values.

week(0) = "Sunday"

week(1) = "Monday"

In the above statement , we initialize the values to the String Array. week(0) = "Sunday" means , we initialize the first value of Array as "Sunday" ,

Dim weekName as String = week(1)

We can access the Arrays elements by providing its numerical index, the above statement we access the second value from the week Array.

In the following program , we declare an Array "week" capability of seven String values and assigns the seven values as days in a week . Next step is to retrieve the elements of the Array using a For loop. For finding the end of an Array we used the Length function of Array Object.

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Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles Button1.Click Dim i As Integer Dim week(6) As String week(0) = "Sunday" week(1) = "Monday" week(2) = "Tuesday" week(3) = "Wednesday" week(4) = "Thursday" week(5) = "Friday" week(6) = "Saturday"

For i = 0 To week.Length - 1 MsgBox(week(i)) Next

End SubEnd Class

The Queue is another adtastructure from VB.NET Collections . It works like FIFO system. That is First In First Out, The item added in Queue is , first get out from Queue. We can Enqueue (add) items in Queue and we can Dequeue (remove from Queue ) or we can Peek (that is get the reference of first item added in Queue ) the item from Queue.

The commonly using functions are follows :Enqueue : Add an Item in Queue

Syntax : Stack.Enqueue(Object)

Object : The item to add in Queue

Dequeue : Remove the oldest item from Queue (we dont get the item later)

Syntax : Stack.Dequeue()

Returns : Remove the oldest item and return.

Peek : Get the reference of the oldest item (it is not removed permenantly)

Syntax : Stack.Peek()

returns : Get the reference of the oldest item in the Queue

The following VB.NET Source code shows some of commonly used functions :

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         How to VB.Net Queue - Download

         VB.Net Tutorial

Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object,_

ByVal e As System.EventArgs) Handles Button1.Click Dim queueList As New Queue queueList.Enqueue("Sun") queueList.Enqueue("Mon") queueList.Enqueue("Tue") queueList.Enqueue("Wed") queueList.Enqueue("Thu") queueList.Enqueue("fri") queueList.Enqueue("Sat") MsgBox(queueList.Dequeue()) MsgBox(queueList.Peek()) If queueList.Contains("Sun") Then MsgBox("Contains Sun ") Else MsgBox("Not Contains Sun ") End If End SubEnd Class

When you execute the program it add seven items in the Queue. Then it Dequeue (remove) the oldest item from queue. Next it Peek() the oldest item from Queue (shows only , not remove ). Next it check the Item "Sun" contains in the Queue.

The Queue is another adtastructure from VB.NET Collections . It works like FIFO system. That is First In First Out, The item added in Queue is , first get out from Queue. We can Enqueue (add) items in Queue and we can Dequeue (remove from Queue ) or we can Peek (that is get the reference of first item added in Queue ) the item from Queue.

The commonly using functions are follows :Enqueue : Add an Item in Queue

Syntax : Stack.Enqueue(Object)

Object : The item to add in Queue

Dequeue : Remove the oldest item from Queue (we dont get the item later)

Syntax : Stack.Dequeue()

Returns : Remove the oldest item and return.

Peek : Get the reference of the oldest item (it is not removed permenantly)

Syntax : Stack.Peek()

returns : Get the reference of the oldest item in the Queue

The following VB.NET Source code shows some of commonly used functions :

         VB.NET Source Code Download           Print Source Code

         How to VB.Net Queue - Download

         VB.Net Tutorial

Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object,_

ByVal e As System.EventArgs) Handles Button1.Click Dim queueList As New Queue queueList.Enqueue("Sun")

queueList.Enqueue("Mon") queueList.Enqueue("Tue") queueList.Enqueue("Wed") queueList.Enqueue("Thu") queueList.Enqueue("fri") queueList.Enqueue("Sat") MsgBox(queueList.Dequeue()) MsgBox(queueList.Peek()) If queueList.Contains("Sun") Then MsgBox("Contains Sun ") Else MsgBox("Not Contains Sun ") End If End SubEnd Class

When you execute the program it add seven items in the Queue. Then it Dequeue (remove) the oldest item from queue. Next it Peek() the oldest item from Queue (shows only , not remove ). Next it check the Item "Sun" contains in the Queue.

Dynamic Arrays can resize the capability of the Array at runtime .when you are in a situation that you do not know exactly the number of elements to store in array while you making the program. In that situations we are using Dynamic Array .

Initial declaration

Dim scores() As Integer

Resizing

ReDim scores(1)

If you want to keep the existing items in the Array , you can use the keyword Preserve .

ReDim Preserve scores(2)

In this case the Array dynamically allocate one more String value and keep the existing values.

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         How to VB.Net Dyanamic Array - Download

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Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles Button1.Click Dim i As Integer Dim scores() As Integer

ReDim scores(1) scores(0) = 100 scores(1) = 200

For i = 0 To scores.Length - 1 MsgBox(scores(i)) Next

ReDim Preserve scores(2)

scores(2) = 300

For i = 0 To scores.Length - 1 MsgBox(scores(i)) Next End SubEnd Class

NameValueCollection is used to store data like Name, Value format. It is very similar to Vb.Net HashTable, HashTable also stores data in Key , value format . NameValueCollection can hold more than one value for a corresponding Key.

Adding new pairs

Add(ByVal name As String, ByVal value As String)

Add("High","80")

Get the value of corresponding Key

GetValues(ByVal name As String) As String()

String values() = GetValues("High")

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Imports System.Collections.SpecializedPublic Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles Button1.Click

Dim markStatus As New NameValueCollection Dim key As String Dim values() As String

markStatus.Add("Very High", "80") markStatus.Add("High", "60") markStatus.Add("medium", "50") markStatus.Add("Pass", "40")

For Each key In markStatus.Keys values = markStatus.GetValues(key) For Each value As String In values MsgBox(key & " - " & value) Next value Next key

End SubEnd Class