Built-In Collection Classes

Introduction to List Classes

Overview

Instead of creating a collection class from scratch or instead of deriving a collection, you can use one of the built-in collection classes of the .NET Framework. To support the creation of any kinds of list, the Microsoft .NET Framework provides the ArrayList and the generic List classes. 

The ArrayList class is defined in the System.Collections namespace while the generic List class is part of the System.Collections.Generic namespace. Therefore, in order to use one of these classes in your application, you can first include its namespace in the file that would perform the list-related operations.

The ArrayList class implements the IList, the ICollection, and the IEnumerable interfaces. The List class implements the generic IList(Of Type), the generic ICollection(Of Type), the generic IEnumerable(Of Type), the IList, the ICollection, and the IEnumerable interfaces.

The ArrayList class is founded as follows:

Public Class ArrayList _
	Implements IList, ICollection, IEnumerable, ICloneable

The generic List class is founded as follows:

Public Class List(Of T) _
	Implements IList(Of T), ICollection(Of T),  _
	IEnumerable(Of T), IList, ICollection, IEnumerable

You can use either the ArrayList or the generic List class to create and manage values for a list. Here is an example of declaring an ArrayList variable:

Imports System.Collections

Public Class Exercise
    Private ListOfNames As ArrayList

    Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        ListOfNames = New ArrayList
    End Sub
End Class

Besides the ability to create a list, both the ArrayList and the List classes have the built-in mechanism for serialization.

The default constructor allows you to create an empty list before adding values to it. If you already have an ICollection-based list, that is, a list created from a class that implements the ICollection interface, you can initialize your ArrayList list with it. To support this, the ArrayList class is equipped with the following constructor:

Public Sub New(c As ICollection)

Here is an example:

Imports System.Collections

Public Class Exercise
    Private ListOfNames As ArrayList

    Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        Dim cbx As ComboBox = New ComboBox

        cbx.Items.Add("Paul Bertrand Yamaguchi")
        cbx.Items.Add("Helene Mukoko")
        cbx.Items.Add("John Hancock")
        cbx.Items.Add("Gertrude Monay")

        ListOfNames = New ArrayList(cbx.Items)
    End Sub
End Class

1. Start Microsoft Visual Basic and create a new Windows Forms Application named CollegeParkAutoParts1
2. To create a dialog box, on the main menu, click Project -> Add Windows Form...
3. Set the name to MakeEditor and click Add
4. Design the form as follows:
    

   Control Text Name Other Properties Label &Make:     TextBox   txtMake Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
   Form Property	Value
   FormBorderStyle	FixedDialog
   Text	Make Editor
   StartPosition	CenterScreen
   AcceptButton	btnOK
   CancelButton	btnCancel
   MaximizeBox	False
   MinimizeBox	False
   ShowInTaskbar	False

5. To create a dialog box, on the main menu, click Project -> Add Windows Form...
6. Set the name to ModelEditor and click Add
7. Design the form as follows:
    

   Control Text Name Other Properties Label &Model:     TextBox   txtModel Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
   Form Property	Value
   FormBorderStyle	FixedDialog
   Text	Model Editor
   StartPosition	CenterScreen
   AcceptButton	btnOK
   CancelButton	btnCancel
   MaximizeBox	False
   MinimizeBox	False
   ShowInTaskbar	False

8. To create a dialog box, in the Solution Explorer, right-click CollegeParkAutoParts1 -> Add -> Windows Form...
9. Set the name to CategoryEditor and click Add
10. Design the form as follows:
     

    Control Text Name Other Properties Label &Category:     TextBox   txtCategory Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
    Form Property	Value
    FormBorderStyle	FixedDialog
    Text	Category Editor
    StartPosition	CenterScreen
    AcceptButton	btnOK
    CancelButton	btnCancel
    MaximizeBox	False
    MinimizeBox	False
    ShowInTaskbar	False

11. On the main menu, click Project -> Add Windows Form...
12. Set the Name to NewStoreItem and click Add
13. Design the form as follows:
     

    Control Text Name Other Properties Label &Year:     TextBox   txtItemNumber   Label &Make:     ComboBox   cbxMakes   Button New C&ategory... btnNewMake   Label M&odel:     ComboBox   cbxModels   Button New Mo &del... btnNewModel   Label &Category:     ComboBox   cbxCategories   Button New Ca&tegory btnNewCategory   Label &Unit Price:     TextBox 0.00 txtUnitPrice TextAlign: Right Label Part #:     TextBox   txtPartNumber   Label &Part Name:     TextBox   txtPartName   Button Submit btnSubmit   Button Close btnClose DialogResult: Cancel
    Form Property	Value
    FormBorderStyle	FixedDialog
    Text	College Park Auto -Parts: Part Editor
    StartPosition	CenterScreen
    MaximizeBox	False
    MinimizeBox	False
    ShowInTaskbar	False

14. Right-click the form and click View Code
15. In the Class Name combo box, select btnNewMake
16. In the Method Name combo box, select Click and implement the event as follows:
      

    Private Sub btnNewMake_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewMake.Click Dim Editor As MakeEditor = New MakeEditor If Editor.ShowDialog() = DialogResult.OK Then If Editor.txtMake.Text.Length > 0 Then Dim strMake As String = Editor.txtMake.Text ' Make sure the category is not yet in the list If cbxMakes.Items.Contains(strMake) Then MsgBox(strMake & " is already in the list") Else ' Since this is a new category, add it to the combo box cbxMakes.Items.Add(strMake) End If cbxMakes.Text = strMake End If End If End Sub

17. In the Class Name combo box, select btnNewModel
18. In the Method Name combo box, select Click and implement the event as follows:
      

    Private Sub btnNewModel_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewModel.Click Dim Editor As ModelEditor = New ModelEditor If Editor.ShowDialog() = DialogResult.OK Then If Editor.txtModel.Text.Length > 0 Then Dim strModel As String = Editor.txtModel.Text ' Make sure the category is not yet in the list If cbxModels.Items.Contains(strModel) Then MsgBox(strModel & " is already in the list") Else ' Since this is a new category, add it to the combo box cbxModels.Items.Add(strModel) End If cbxModels.Text = strModel End If End If End Sub

19. In the Class Name combo box, select btnNewCategory
20. In the Method Name combo box, select Click and implement the event as follows:
      

    Private Sub btnNewCategory_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewCategory.Click Dim Editor As CategoryEditor = New CategoryEditor If Editor.ShowDialog() = DialogResult.OK Then If Editor.txtCategory.Text.Length > 0 Then Dim strCategory As String = Editor.txtCategory.Text ' Make sure the category is not yet in the list If cbxCategories.Items.Contains(strCategory) Then MsgBox(strCategory & " is already in the list") Else ' Since this is a new category, add it to the combo box cbxCategories.Items.Add(strCategory) End If cbxCategories.Text = strCategory End If End If End Sub

21. Save the file
22. To create an icon, on the main menu, click Project -> Add New Item...
23. In the Templates list, click Icon File
24. Set the Name to cpap1 and click Add
25. Right-click the white area and click Delete Image Type
26. Design the 16x16, 16 colors version of the icon as follows:
     
    
27. On the main menu, click File -> Save cpap1.ico As
28. Select the bin\Debug folder of the current folder and click Save
29. On the main menu, click File -> Close
30. In the Solution Explorer, expand bin and expand Debug
31. In the Solution Explorer, right-click the Debug folder -> Add -> New Item...
32. In the Templates list, make sure Icon File is selected.
    Set the Name to cpap2 and click Add
33. Right-click the white area and click Delete Image Type
34. Design the 16x16, 16 colors version of the icon as follows:
     
    
35. Save the file and close the icon window
36. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
37. In the Templates list, make sure Icon File is selected.
    Set the Name to year1 and click Add
38. Right-click the white area and click Delete Image Type
39. Design the 16x16, 16 colors version of the icon as follows:
     
    
40. Save the file and close the icon window
41. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
42. In the Templates list, make sure Icon File is selected.
    Set the Name to year2 and click Add
43. Right-click the white area and click Delete Image Type
44. Design the 16x16, 16 colors version of the icon as follows:
     
    
45. Save the file and close the icon window
46. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
47. In the Templates list, make sure Icon File is selected.
    Set the Name to make1 and click Add
48. Right-click the white area and click Delete Image Type
49. Design the 16x16, 16 colors version of the icon as follows:
     
    
50. Save the file and close the icon window
51. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
52. In the Templates list, make sure Icon File is selected.
    Set the Name to make2 and click Add
53. Right-click the white area and click Delete Image Type
54. Design the 16x16, 16 colors version of the icon as follows:
     
    
55. Save the file and close the icon window
56. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
57. In the Templates list, make sure Icon File is selected.
    Set the Name to model1 and click Add
58. Right-click the white area and click Delete Image Type
59. Design the 16x16, 16 colors version of the icon as follows:
     
    
60. Save the file and close the icon window
61. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
62. In the Templates list, make sure Icon File is selected.
    Set the Name to model2 and click Add
63. Right-click the white area and click Delete Image Type
64. Design the 16x16, 16 colors version of the icon as follows:
     
    
65. Save the file and close the icon window
66. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
67. In the Templates list, make sure Icon File is selected.
    Set the Name to category1 and click Add
68. Right-click the white area and click Delete Image Type
69. Design the 16x16, 16 colors version of the icon as follows:
     
    
70. Save the file and close the icon window
71. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
72. In the Templates list, make sure Icon File is selected.
    Set the Name to category2 and click Add
73. Right-click the white area and click Delete Image Type
74. Design the 16x16, 16 colors version of the icon as follows:
     
    
75. Save the file and close the icon window
76. In the Solution Explorer, right-click Form1.vb and click Rename
77. Type Central.vb and press Enter twice to display the Central form
78. From the Components section of the Toolbox, click ImageList and click the form
79. In the Properties window, click (Name) and type AutoPartsImages
80. Click the ellipsis button of the Images field
81. In the Image Collection Editor, click Add
82. Locate the folder that contains the icons you created and display it in the Look In combo box
83. Select cpap1.ico and click Open
84. In the same way, add the other pictures in the following order: cpap2.ico, year1.ico, year2.ico, make1.ico, make2.ico, model1.ico, model2.ico, category1.ico, and category1.ico
     
    
85. Click OK
86. Design the form as follows:
     

    Control Text Name Other Properties Label College Park Auto-Parts   Font: Times New Roman, 20.25pt, style=Bold ForeColor: Blue Panel     Height: 2 GroupBox Part Identification     TreeView   tvwAutoParts ImageList: imgAutoParts GroupBox Available Parts     ListView   lvwAutoParts FullRowSelect: True GridLines: True View: Details Columns   (Name) Text TextAlign Width colPartNumber Part #     colPartName Part Name   300 colUnitPrice Unit Price Right 80 GroupBox Customer Order - Selected Parts     Label Part #     Label Part Name     Label Unit Price     Label Qty     Label Sub Total     TextBox   txtPartNumber   TextBox   txtPartName   TextBox 0.00 txtUnitPrice TextAlign: Right TextBox 0 txtQuantity TextAlign: Right TextBox 0.00 txtSubTotal TextAlign: Right Button Add/Select btnAdd ListView   lvwSelectedParts FullRowSelect: True GridLines: True View: Details Columns   (Name) Text TextAlign Width colPartNumberSelected Part #   45 colPartNameSelected Part Name   274 colUnitPriceSelected Unit Price Right 58 colQuantitySelected Qty Right 28 colSubTotalSelected Sub-Total Right 58 GroupBox Order Summary Button New Au&to Part... btnNewAutoPart   Label Receipt #:   TextBox txtSave Button Save btnSave Label Tax Rate: TextBox 7.75 txtTaxRate TextAlign: Right Label % Label Parts Total: TextBox 0.00 txtPartsTotal TextAlign: Right Button &New Customer Order btnNewCustomerOrder   Label Receipt #:   TextBox txtOpen Button Save btnSave Label Tax Amount: TextBox 0.00 txtTaxAmount TextAlign: Right Label Order Total: TextBox 0.00 txtOrderTotal TextAlign: Right Button Close btnClose

87. Right-click the table and click Form View
88. In the Class Name combo box, select lvwAutoParts
89. In the Method Name combo box, select DoubleClick and implement the event as follows:
     

    Private Sub lvwAutoParts_DoubleClick(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lvwAutoParts.DoubleClick Dim lviAutoPart As ListViewItem = lvwAutoParts.SelectedItems(0) If (lvwAutoParts.SelectedItems.Count = 0) Or _ (lvwAutoParts.SelectedItems.Count > 1) Then Exit Sub End If txtPartNumber.Text = lviAutoPart.Text txtPartName.Text = lviAutoPart.SubItems(1).Text txtUnitPrice.Text = lviAutoPart.SubItems(2).Text txtQuantity.Text = "1" txtSubTotal.Text = lviAutoPart.SubItems(2).Text txtQuantity.Focus() End Sub

90. In the Class Name combo box, select txtUnitPrice
91. In the Method Name combo box, select Leave and implement the event as follows:
     

    Private Sub txtUnitPrice_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtUnitPrice.Leave, _ txtQuantity.Leave Dim UnitPrice As Double Dim Quantity As Integer Dim SubTotal As Double Try UnitPrice = CDbl(txtUnitPrice.Text) Catch Exc As FormatException MsgBox("Invalid Unit Price!") End Try Try Quantity = CInt(txtQuantity.Text) Catch Exc As FormatException MsgBox("Invalid Quandtity!") End Try SubTotal = UnitPrice * Quantity txtSubTotal.Text = FormatNumber(SubTotal) End Sub Public Sub CalculateOrder() ' Calculate the current total order and update the order Dim PartsTotal As Double Dim TaxRate As Double Dim TaxAmount As Double Dim OrderTotal As Double Dim SubItem As ListViewItem.ListViewSubItem Dim lviAutoPart As ListViewItem For Each lviAutoPart In lvwSelectedParts.Items SubItem = lviAutoPart.SubItems(4) PartsTotal = PartsTotal + CDbl(SubItem.Text) Next Try TaxRate = CDbl(txtTaxRate.Text) / 100 Catch Exc As FormatException MsgBox("Invalid Tax Rate") End Try TaxAmount = PartsTotal * TaxRate OrderTotal = PartsTotal + TaxAmount txtPartsTotal.Text = FormatNumber(PartsTotal) txtTaxAmount.Text = FormatNumber(TaxAmount) txtOrderTotal.Text = FormatNumber(OrderTotal) End Sub

92. In the Class Name combo box, select lvwSelectedParts
93. In the Method Name combo box, select DoubleClick and implement the event as follows:
     

    Private Sub lvwSelectedParts_DoubleClick(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lvwSelectedParts.DoubleClick Dim lviSelectedPart As ListViewItem = lvwSelectedParts.SelectedItems(0) If (lvwSelectedParts.SelectedItems.Count = 0) Or _ (lvwSelectedParts.SelectedItems.Count > 1) Then Exit Sub End If txtPartNumber.Text = lviSelectedPart.Text txtPartName.Text = lviSelectedPart.SubItems(1).Text txtUnitPrice.Text = lviSelectedPart.SubItems(2).Text txtQuantity.Text = lviSelectedPart.SubItems(3).Text txtSubTotal.Text = lviSelectedPart.SubItems(4).Text lvwSelectedParts.Items.Remove(lviSelectedPart) CalculateOrder() End Sub

94. In the Solution Explorer, right-click CollegeParkAutoParts1 -> Add -> Class...
95. Set the name to PartDescription and press Enter
96. To create a class that can hold a structured item of a list, change the class as follows:
     

    <Serializable()> Public Class PartDescription ' These members will be used to define a car part Private ID As Long Private yr As Integer Private mk As String Private mdl As String Private cat As String Private name As String Private price As Double Public Sub New() ID = 0 yr = 1960 mk = "" mdl = "" name = "Unknown" price = 0.0 End Sub Public Sub New(ByVal code As Long, ByVal year As Integer, _ ByVal make As String, ByVal model As String, _ ByVal type As String, ByVal desc As String, _ ByVal UPrice As Double) ID = code yr = year mk = make mdl = model cat = type name = desc price = UPrice End Sub Public Property PartNumber() As Long Get Return ID End Get Set(ByVal value As Long) ID = value End Set End Property Public Property Year() As Integer Get Return yr End Get Set(ByVal value As Integer) yr = value End Set End Property Public Property Make() As String Get Return mk End Get Set(ByVal value As String) mk = value End Set End Property Public Property Model() As String Get Return mdl End Get Set(ByVal value As String) mdl = value End Set End Property Public Property Category() As String Get Return cat End Get Set(ByVal value As String) cat = value End Set End Property Public Property PartName() As String Get Return name End Get Set(ByVal value As String) name = value End Set End Property Public Property UnitPrice() As Double Get Return price End Get Set(ByVal value As Double) price = value End Set End Property Public Overrides Function ToString() As String Return PartNumber & " " & _ CStr(Year) & " " & _ Make & " " & _ Model & " " & _ Category & " " & _ PartName & " " & _ UnitPrice End Function End Class

97. In the Solution Explorer, right-click CollegeParkAutoParts1 -> Add -> Class...
98. Set the name to PartOrdered and press Enter
99. To create another class independent for a list, change the document as follows:
     

    <Serializable()> Public Class PartOrdered Public PartNumber As Long Public PartName As String Public UnitPrice As Double Public Quantity As Integer Public SubTotal As Double End Class

100. Save all

After declaring an ArrayList or a List variable, it is empty. As objects are added to it, the list grows. The list can grow tremendously as you wish. The number of items of the list is managed through the memory it occupies and this memory grows as needed. The number of items that the memory allocated is currently using is represented by the Capacity property. Here is an example of accessing the ArrayList.Capacity property:

Imports System.Collections

Public Class Exercise
    Private ListOfNames As ArrayList

    Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        ListOfNames = New ArrayList

        Text = "List Capacity: " & ListOfNames.Capacity
    End Sub
End Class

This would produce:

The capacity of a list will usually be the least of your concerns. If for some reason, you want to intervene and control the number of items that your list can contain, you can manipulate the Capacity property. For example, you can assign it a constant to set the maximum value that the list can contain. Instead of specifying the capacity after the list has been created, when declaring the list variable, you can specify its maximum capacity. To support this, both the ArrayList and the List classes are equipped with an additional constructor as follows:

Public Sub New(capacity As Integer)
Public Sub New(capacity As Integer)

Once again, you will hardly have any reason to use the Capacity property: the compiler knows what to do with it.

One of the reason for creating a list is to be able to add values to it, edit its values, retrieve a value, or delete values from it. These are the default operations. You can still limit these operations as you judge them unnecessary. For example, you may create a list and then initialize it with the values that you want the list to only have. If you do not want to have the user adding values to it, you can create the list as read-only. To do this, you can call the ArrayList.ReadOnly() method. It is overloaded with two versions as follows:

Public Shared Function ReadOnly(list As ArrayList) As ArrayList
Public Shared Function ReadOnly(list As IList) As IList

Some operations cannot be performed on a read-only list. To perform such operations, you can first find out whether an ArrayList list is read-only. This is done by checking its IsReadOnly property.

The primary operation performed on a list is to create one or more values. To do this, you have various alternatives. Both the ArrayList and the List classes are equipped with an Add() method. The syntax of the System.Collections.ArrayList.Add() method is:

Public Overridable Function Add(value As Object) As Integer

The syntax of the System.Collections.Generic.List.Add() method is:

Public Sub Add(item As T)

The argument of the method is the value to add to the list. If the method succeeds with the addition, it returns the position where the value was added in the list. Here are example for an ArrayList variable:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        ListOfNames = New ArrayList

        ListOfNames.Add("Christine Kingston")
        ListOfNames.Add("Hermine Paulson")
        ListOfNames.Add("William Harrison")
        ListOfNames.Add("Ursula Morales")
        ListOfNames.Add("Evan Lancos")
End Sub

If the method fails to add the value and if you are using the ArrayList class, the compiler would throw an error. One of the errors that could result from the ArrayList's failure of this operation would be based on the fact that either a new value cannot be added to the list because the list is read-only, or the list was already full prior to adding the new value. Normally, a list can be full only if you had specified the maximum number of items it can contain using the ArrayList.Capacity property. As mentioned above, the list can be made read-only by passing its variable to the ArrayList.ReadOnly() method.

Instead of adding one values at a time, you can first create a list of values and add that whole list at once. To support this operation, both the ArrayList and the List classes are equipped with a method named AddRange.

The syntax of the ArrayList.AddRange() method is:

Public Overridable Sub AddRange(c As ICollection)

The syntax of the List.AddRange() method is:

Public Sub AddRange(collection As IEnumerable(Of T))

The ArrayList.AddRange() method takes as argument a list created from a class that implements the ICollection interface. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        Dim cbx As ComboBox = New ComboBox
        cbx.Items.Add("Paul Bertrand Yamaguchi")
        cbx.Items.Add("Helene Mukoko")
        cbx.Items.Add("John Hancock")
        cbx.Items.Add("Gertrude Monay")

        ListOfNames = New ArrayList
        ListOfNames.AddRange(cbx.Items)
End Sub

The List.AddRange() method takes as argument a list created from a class that implements the generic IEnumerable interface.

1. In the Solution Explorer, right-click NewStoreItem and click View Code
2. Add the following lines:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class NewStoreItem Private ListOfAutoParts As List(Of PartDescription)

3. In the Class Name combo box, select btnSubmit
4. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnSubmit_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnSubmit.Click Dim stmAutoParts As FileStream Dim bfmAutoParts As BinaryFormatter = New BinaryFormatter ' If this directory doesn't exist, create it Directory.CreateDirectory("C:\College Park Auto Parts") ' This is the file that holds the list of items Dim FileName As String = "C:\College Park Auto Parts\Parts.prs" ' Create a random number that will be used to identify the item Dim RndNumber As Random = New Random() txtPartNumber.Text = RndNumber.Next(100000, 999999).ToString() ' Make sure the user had selected a make If cbxYears.Text.Length = 0 Then MsgBox("You must specify the year") cbxYears.Focus() Exit Sub End If ' Make sure the user had selected a make If cbxMakes.Text.Length = 0 Then MsgBox("You must specify the car name") cbxMakes.Focus() Exit Sub End If ' Make sure the user had selected a model If cbxModels.Text.Length = 0 Then MsgBox("You must specify the model of the car") cbxModels.Focus() Exit Sub End If ' Make sure the user had selected the part category If cbxCategories.Text.Length = 0 Then MsgBox("You must specify the part's category") cbxCategories.Focus() Exit Sub End If ' Make sure the user had entered a name/description If txtPartName.Text.Length = 0 Then MsgBox("You must enter the name (or a " & _ "short description) for the part") txtPartName.Focus() Exit Sub End If ' Make sure the user had typed a price for the item If txtUnitPrice.Text.Length = 0 Then MsgBox("You must enter the price of the item") txtUnitPrice.Focus() Exit Sub End If ' Before saving the new part, find out if there was ' already a file that holds the list of parts ' If that file exists, open it and store its parts ' in our ListOfParts variable If File.Exists(FileName) Then stmAutoParts = New FileStream(FileName, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try ' Retrieve the list of items from file ListOfAutoParts = CType(bfmAutoParts.Deserialize(stmAutoParts), _ List(Of PartDescription)) Finally stmAutoParts.Close() End Try End If ' Create the part Dim Part As PartDescription = New PartDescription Part.PartNumber = CLng(txtPartNumber.Text) Part.Year = CInt(cbxYears.Text) Part.Make = cbxMakes.Text Part.Model = cbxModels.Text Part.Category = cbxCategories.Text Part.PartName = txtPartName.Text Part.UnitPrice = CDbl(txtUnitPrice.Text) ' Call the Add method of our collection class to add the part ListOfAutoParts.Add(Part) ' Save the list stmAutoParts = New FileStream(FileName, _ FileMode.Create, _ FileAccess.Write, _ FileShare.Write) Try bfmAutoParts.Serialize(stmAutoParts, ListOfAutoParts) ' After saving the item, reset the form cbxYears.Text = "" cbxMakes.Text = "" cbxModels.Text = "" cbxCategories.Text = "" txtPartName.Text = "" txtUnitPrice.Text = "0.00" txtPartNumber.Text = RndNumber.Next(100000, 999999).ToString() Finally stmAutoParts.Close() End Try End Sub

5. In the Solution Explorer, right-click Central.vb and click View Code
6. Add the following namespaces in the top section of the file and declare the two variables:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class Central Private iFileName As Integer Private ListOfAutoParts As List(Of PartDescription)

7. In the Class Name combo box, select btnSaveCustomerOrder
8. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnSave_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnSave.Click Dim i As Integer Dim Part As PartsOrdered Dim bfmCustomerOrder As BinaryFormatter = New BinaryFormatter ' We will store our files in the following folder Dim FolderName As String = "C:\College Park Auto Parts\Receipts" Dim Folder As DirectoryInfo = New DirectoryInfo(FolderName) Dim strFilename As String = FolderName & "\" & txtSave.Text & ".cap" Dim ListOfOrderedParts As List(Of PartsOrdered) If lvwSelectedParts.Items.Count = 0 Then Exit Sub Else ListOfOrderedParts = New List(Of PartsOrdered) For i = 0 To lvwSelectedParts.Items.Count - 1 Part = New PartsOrdered Part.PartNumber = CLng(lvwSelectedParts.Items(i).Text) Part.PartName = lvwSelectedParts.Items(i).SubItems(1).Text Part.UnitPrice = CDbl(lvwSelectedParts.Items(i).SubItems(2).Text) Part.Quantity = CInt(lvwSelectedParts.Items(i).SubItems(3).Text) Part.SubTotal = CDbl(lvwSelectedParts.Items(i).SubItems(4).Text) ListOfOrderedParts.Add(Part) Next Dim stmCustomerOrder As FileStream = New FileStream(strFilename, _ FileMode.Create) Try bfmCustomerOrder.Serialize(stmCustomerOrder, ListOfOrderedParts) Finally stmCustomerOrder.Close() End Try End If End Sub

9. Save all

When using a list, at any time, you should be able to know the number of items that the list contains. This information is provided by the ArrayList.Count or the List.Count property.

The Capacity and the Count properties have this in common: the value of each increases as the list grows and the same value decreases if the list shrinks. It is important to know that there are various differences between the capacity of a list and the number of items it contains:

• Capacity is a read/write property. This means that you can assign a value to the capacity to fix the number of items that the list can contain. You can also retrieve the value of the Capacity
• The Count property is read-only because it is used by the compiler to count the current number of values of the list and this counting is performed without your intervention

Once a list is ready, you can perform different types of operations on it. Besides adding items, one of the most regular operations performed on a list consists of locating and retrieving its values. You have various options.

To give you access to each member of their list, both the ArrayList and the List classes are equipped with the default Item property. The first value of the list has an index of 0. The second has an index of 1, and so on. 

To retrieve a single value based on its position, you can apply the parentheses of arrays to the variable. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        Dim i As Integer
        ListOfNames = New ArrayList

        ListOfNames.Add("Christine Kingston")
        ListOfNames.Add("Hermine Paulson")
        ListOfNames.Add("William Harrison")
        ListOfNames.Add("Ursula Morales")
        ListOfNames.Add("Evan Lancos")

        For i = 0 To 4
            lbxNames.Items.Add(ListOfNames(i))
        Next

End Sub

Another issue to keep in mind is that the ArrayList.Item() property returns an Object value. Therefore, you may have to cast this value to your type of value to get it right.

Besides using the index to access a value from the list, the ArrayList and the List classes implement the IEnumerable.GetEnumerator() method. For this reason, you can use the For Each loop to access each member of the collection. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        Dim strName As String
        ListOfNames = New ArrayList

        ListOfNames.Add("Christine Kingston")
        ListOfNames.Add("Hermine Paulson")
        ListOfNames.Add("William Harrison")
        ListOfNames.Add("Ursula Morales")
        ListOfNames.Add("Evan Lancos")

        For Each strName In ListOfNames
            lbxNames.Items.Add(strName)
        Next
End Sub

You can use the Item property to change a value in the list. Because the Item property is used to access an existing value from the list, the value must have been created. If you try setting the value of a non existing item, the compiler would throw an ArgumentOutOfRangeException Exception. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        ListOfNames = New ArrayList

        ListOfNames(0) = "Paul Bertrand Yamaguchi"
End Sub

Notice that at the time the 0 item is accessed, it has not previous been created. This would produce:

A review of the Details section shows:

System.ArgumentOutOfRangeException: Index was out of range. 
Must be non-negative and less than the size of the collection.
Parameter name: index
at System.Collections.ArrayList.set_Item(Int32 index, Object value)
at Exercise.StartForm(Object sender, EventArgs e) 
in E:\Programs\vb\Exercise1\Exercise1\Exercise.cs:line 31

This means that you can use the Item property only to change the value of a previous created item.

1. In the Solution Explorer, right-click NewStoreItem.vb and click View Code
2. In the Class Name combo box, select cbxMakes
3. In the Method Name combo box, select SelectedIndexChanged and implement its event as follows:
    

   Private Sub cbxMakes_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles cbxMakes.SelectedIndexChanged cbxModels.Text = "" cbxModels.Items.Clear() Dim Part As PartDescription For Each Part In ListOfAutoParts If Part.Make = cbxMakes.Text Then If Not cbxModels.Items.Contains(Part.Model) Then cbxModels.Items.Add(Part.Model) End If End If Next End Sub

4. In the Solution Explorer, right-click Central.vb and click View Code
5. In the Class Name, select btnAdd
6. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnAdd_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnAdd.Click Dim Part As PartDescription Dim lviSelectedPart As ListViewItem REM If the user didn't enter a part number, don't do anything If txtPartNumber.Text.Length = 0 Then MsgBox("There is no part to be added to the order") Exit Sub End If REM Since the user entered a part, check each item in the list of parts For Each Part In ListOfAutoParts REM If you find a part number that corresponds to the user's entry ... If Part.PartNumber = CLng(txtPartNumber.Text) Then REM ... display it in the Selected Parts list view lviSelectedPart = New ListViewItem(Part.PartNumber) lviSelectedPart.SubItems.Add(Part.PartName) lviSelectedPart.SubItems.Add(Part.UnitPrice) lviSelectedPart.SubItems.Add(txtQuantity.Text) lviSelectedPart.SubItems.Add(txtSubTotal.Text) lvwSelectedParts.Items.Add(lviSelectedPart) End If Next REM Update the order evaluation CalculateOrder() End Sub

7. In the Class Name, select btnOpen
8. In the Method Name combo box, select Click and implement its event as follows:
    

   Private Sub btnOpen_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnOpen.Click Dim Part As PartOrdered Dim strFilename As String Dim lviReceiptPart As ListViewItem Dim ListOfReceipts As List(Of PartOrdered) Dim ReceiptsFormatter As BinaryFormatter = New BinaryFormatter() Dim StreamReceipts As FileStream = Nothing REM Identify the folder where the receipts are stored Dim FolderName As String = "C:\College Park Auto Parts\Receipts" REM Get a reference to the receipts Dim dirReceipts As DirectoryInfo = New DirectoryInfo(FolderName) REM Get the list of receipts in the folder Dim fleReceipts() As FileInfo = dirReceipts.GetFiles() REM Check that the user entered a receipt number REM If not, don't do anything If txtOpen.Text.Length = 0 Then MsgBox("You must enter a receipt number" & vbCrLf & _ "There is no receipt number to " & _ "open a customer's order") txtOpen.Focus() Exit Sub End If REM If no receipt was created before, let the user know If fleReceipts.Length = 0 Then MsgBox("There is no customer order to open") txtOpen.Focus() Exit Sub Else REM Since there is at least one receipt, REM get ready to use it/them lvwAutoParts.Items.Clear() lvwSelectedParts.Items.Clear() REM Create a file name using the path to the folder, REM the receipt number, and the .cap extension strFilename = FolderName & "\" & txtOpen.Text & ".cap" REM Check if there is a file with that receipt number If File.Exists(strFilename) Then Try REM If so, retrieve the contents of that file StreamReceipts = New FileStream(strFilename, FileMode.Open) ListOfReceipts = CType(ReceiptsFormatter.Deserialize(StreamReceipts), _ List(Of PartOrdered)) REM And display the contents of that receipt number in REM the Selected Parts list view For Each Part In ListOfReceipts lviReceiptPart = New ListViewItem(Part.PartNumber) lviReceiptPart.SubItems.Add(Part.PartName) lviReceiptPart.SubItems.Add(FormatNumber(Part.UnitPrice)) lviReceiptPart.SubItems.Add(Part.Quantity) lviReceiptPart.SubItems.Add(FormatNumber(Part.SubTotal)) lvwSelectedParts.Items.Add(lviReceiptPart) Next Finally StreamReceipts.Close() End Try REM Just in case, update the calculation CalculateOrder() REM In case the user will modify the file that was opened, REM put its receipt number in the Save text box txtSave.Text = txtOpen.Text Else REM Since it appears that the user entered an invalid receipt number REM let him/her know MsgBox("There is no customer order with that receipt number") End If End If End Sub

9. Save the file

Instead of the parentheses that allow you to retrieve a value based on its position, you can look for a value based on its complete definition. You have various options. You can first "build" an item and ask the compiler to check whether any item in the list matches your definition. To perform this search, depending on your class, you can call either the ArrayList.Contains() or the List.Contains() method. The syntax of the System.Collections.ArrayList.Contains() method is:

Public Overridable Function Contains(item As Object) As Boolean

The syntax of the System.Collections.Generic.List.Contains() method is:

Public Function Contains(item As T) As Boolean

The value to look for is passed as argument to the method. The compiler would look for exactly the value, using its definition, in the list. If any detail of the argument fails to match any value of the list, the method would return False. If all characteristics of the argument correspond to a value of the list, the method returns True. Here is an example:

Imports System.Collections

Public Class Exercise
    Private ListOfNames As ArrayList

    Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) _
                              Handles Me.Load
        ListOfNames = New ArrayList

        ListOfNames.Add("Christine Kingston")
        ListOfNames.Add("Hermine Paulson")
        ListOfNames.Add("William Harrison")
        ListOfNames.Add("Ursula Morales")
        ListOfNames.Add("Evan Lancos")

        For Each strName As String In ListOfNames
            lbxNames.Items.Add(strName)
        Next
    End Sub

    Private Sub btnResult_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles btnResult.Click
        Dim strFind As String = txtLookFor.Text

        If ListOfNames.Contains(strFind) = True Then
            txtResult.Text = "Found"
        Else
            txtResult.Text = "Not Found"
        End If
    End Sub
End Class

1. In the Solution Explorer, right-click NewStoreItem.vb and click View Code
2. In the Class Name combo box, select (NewStoreItem Events)
3. In the Method Name combo box, select Load and implement the event as follows:
    

   Private Sub NewStoreItem_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load REM Since all values seem ready, prepare to process the item Dim i As Integer Dim Part As PartDescription Dim RndNumber As Random = New Random Dim StreamAutoParts As FileStream = Nothing Dim bfmAutoParts As BinaryFormatter = New BinaryFormatter ListOfAutoParts = New List(Of PartDescription) For i = DateTime.Today.Year + 1 To 1960 Step -1 cbxYears.Items.Add(i) Next REM Create a random number that will be used to identify the item txtPartNumber.Text = RndNumber.Next(100000, 999999) REM This is the file that holds the list of parts Dim FileName As String = "C:\College Park Auto Parts\Parts.prs" If File.Exists(FileName) Then StreamAutoParts = New FileStream(FileName, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the list of items from file ListOfAutoParts = CType(bfmAutoParts.Deserialize(StreamAutoParts), _ List(Of PartDescription)) REM Display the car manufacturers in the Make combo box For i = 0 To ListOfAutoParts.Count - 1 Part = CType(ListOfAutoParts(i), PartDescription) If Not cbxMakes.Items.Contains(Part.Make) Then cbxMakes.Items.Add(Part.Make) End If Next REM Display the pats categories in the Category combo box For i = 0 To ListOfAutoParts.Count - 1 Part = CType(ListOfAutoParts(i), PartDescription) If Not cbxCategories.Items.Contains(Part.Category) Then cbxCategories.Items.Add(Part.Category) End If Next Finally StreamAutoParts.Close() End Try End If End Sub

4. In the Solution Explorer, right-click Central.vb and click View Code
5. In the Class Name combo box, select txtPartNumber
6. In the Method name combo box, select Leave and implement the event as follows:
    

   Private Sub txtPartNumber_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtPartNumber.Leave Dim Part As PartDescription ' We will allow the user to enter a part number ' In the beginning, we assume that the user ' had entered an invalid number Dim Found As Boolean = False ' This will represent the part found, if any Dim PartFound As PartDescription = Nothing ' After the user had entered a part number, ' check the whole list of parts For Each Part In ListOfAutoParts ' If you find a part that holds the number the user had entered If Part.PartNumber = CLng(txtPartNumber.Text) Then ' Mark that part PartFound = Part ' And update the flag that specifies that the part has been found Found = True End If ' If the part number was not found, check the next Next ' If no part has that number, the found flag keeps marked as False ' If a part with that number was found... If Found = True Then ' Show the corresponding part name and unit price txtPartName.Text = PartFound.PartName txtUnitPrice.Text = FormatNumber(PartFound.UnitPrice) txtQuantity.Text = "1" txtSubTotal.Text = FormatNumber(PartFound.UnitPrice) ' Give focus to the quantity in case the user was to increase it txtQuantity.Focus() Else ' Since no part with that number was found, ' reset the text boxes txtPartName.Text = "" txtUnitPrice.Text = "0.00" txtQuantity.Text = "0" txtSubTotal.Text = "0.00" ' Let the user know that the part number that ' was entered is not in the list MsgBox("There is no part with that number") End If End Sub

7. Under the above End Sub line, create the following procedure:
    

   Public Sub ShowAutoParts() Dim Years As Integer Dim NodeYear Dim NodeMake As TreeNode Dim NodeModel As TreeNode Dim Part As PartDescription Dim StreamAutoParts As FileStream Dim bfmAutoParts As BinaryFormatter = New BinaryFormatter tvwAutoParts.Nodes.Clear() Dim RootElement As TreeNode = _ tvwAutoParts.Nodes.Add("College Park Auto-Parts", _ "College Park Auto-Parts", 0, 1) ' Show the years nodes For Years = DateTime.Today.Year + 1 To 1960 Step -1 RootElement.Nodes.Add(CStr(Years), CStr(Years), 2, 3) Next tvwAutoParts.SelectedNode = RootElement ' Expand the root node tvwAutoParts.ExpandAll() ListOfAutoParts = New List(Of PartDescription) ' This is the file that holds the list of auto parts Dim Filename As String = "C:\College Park Auto Parts\Parts.prs" If File.Exists(FileName) Then StreamAutoParts = New FileStream(Filename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try ' Retrieve the list of parts from file ListOfAutoParts = CType(bfmAutoParts.Deserialize(StreamAutoParts), _ List(Of PartDescription)) ' Show the makes nodes For Each NodeYear In RootElement.Nodes Dim ListOfMakes As List(Of String) = New List(Of String) For Each Part In ListOfAutoParts If NodeYear.Text = Part.Year.ToString() Then If Not ListOfMakes.Contains(Part.Make) Then ListOfMakes.Add(Part.Make) End If End If Next For Each strMake As String In ListOfMakes NodeYear.Nodes.Add(strMake, strMake, 4, 5) Next Next ' Showing the models nodes For Each NodeYear In RootElement.Nodes For Each NodeMake In NodeYear.Nodes Dim ListOfModels As List(Of String) = New List(Of String) For Each Part In ListOfAutoParts If (NodeYear.Text = CStr(Part.Year)) And _ (NodeMake.Text = Part.Make) Then If Not ListOfModels.Contains(Part.Model) Then ListOfModels.Add(Part.Model) End If End If Next For Each strModel As String In ListOfModels NodeMake.Nodes.Add(strModel, strModel, 6, 7) Next Next Next ' Showing the categories nodes For Each NodeYear In RootElement.Nodes For Each NodeMake In NodeYear.Nodes For Each NodeModel In NodeMake.Nodes Dim ListOfCategories As List(Of String) = New List(Of String) For Each Part In ListOfAutoParts If (NodeYear.Text = CStr(Part.Year)) And _ (NodeMake.Text = Part.Make) And _ (NodeModel.Text = Part.Model) Then If Not ListOfCategories.Contains(Part.Category) Then ListOfCategories.Add(Part.Category) End If End If Next For Each strCategory As String In ListOfCategories NodeModel.Nodes.Add(strCategory, strCategory, 8, 9) Next Next Next Next Finally StreamAutoParts.Close() End Try End If End Sub

8. In the Class Name combo box, select btnNewAutoPart
9. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnNewAutoPart_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewAutoPart.Click Dim Editor As NewStoreItem = New NewStoreItem If Editor.ShowDialog() = DialogResult.Cancel Then ShowAutoParts() End If End Sub

10. In the Class Name combo box, select btnNewCustomerOrder
11. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnNewCustomerOrder_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewCustomerOrder.Click ' We will store our files in the following folder Dim FolderName As String = "C:\College Park Auto Parts\Receipts" Dim Folder As DirectoryInfo = Directory.CreateDirectory(FolderName) ' Get the list of files, if any, from our directory Dim ListOfFiles() As FileInfo = Folder.GetFiles() ' If there is no file in the directory, ' then we will use 1000 as the first file name If ListOfFiles.Length = 0 Then iFileName = 1000 Else ' If there was at least one file in the directory ' Get a reference to the last file Dim LastFile As FileInfo = ListOfFiles(ListOfFiles.Length - 1) ' Get the name of the last file without its extension Dim fwe As String = Path.GetFileNameWithoutExtension(LastFile.FullName) ' Increment the name of the file by 1 iFileName = CInt(fwe) + 1 End If txtSave.Text = iFileName.ToString() lvwAutoParts.Items.Clear() lvwSelectedParts.Items.Clear() End Sub

12. In the Class Name combo box, select (Central Events)
13. In the Method Name combo box, select Load and implement the event as follows:
     

    Private Sub Central_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load ShowAutoParts() btnNewCustomerOrder_Click(sender, e) End Sub

14. In the Class Name combo box, select tvwAutoParts
15. In the Method Name combo box, select NodeMouseClick and implement the event as follows:
     

    Private Sub tvwAutoParts_NodeMouseClick(ByVal sender As Object, _ ByVal e As System.Windows.Forms.TreeNodeMouseClickEventArgs) _ Handles tvwAutoParts.NodeMouseClick Dim Part As PartDescription Dim lviAutoPart As ListViewItem Dim NodeClicked As TreeNode = e.Node If NodeClicked.Level = 4 Then lvwAutoParts.Items.Clear() End If Try For Each Part In ListOfAutoParts If (Part.Category = NodeClicked.Text) And _ (Part.Model = NodeClicked.Parent.Text) And _ (Part.Make = NodeClicked.Parent.Parent.Text) And _ (CStr(Part.Year) = NodeClicked.Parent.Parent.Parent.Text) Then lviAutoPart = New ListViewItem(Part.PartNumber) lviAutoPart.SubItems.Add(Part.PartName) lviAutoPart.SubItems.Add(FormatNumber(Part.UnitPrice)) lvwAutoParts.Items.Add(lviAutoPart) End If Next Catch Exc As NullReferenceException End Try End Sub

16. In the Class Name combo box, select btnClose
17. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub

18. Execute the application
19. Click the New Auto Part button and use the Part Editor to create a few parts (let the computer generate the part numbers)
     
20. Close the Part Editor
21. Create a few customer part orders and save them:
     
    
     
    
22. Close the forms and return to your programming environment
23. Execute the application again and open a previously saved order
24. Close the forms and return to your programming environment

Another option to look for an item in a list consists of calling the BinarySearch() method of either the ArrayList or the List class. It is overloaded in three versions and one of them uses the following syntax:

Public Overridable Function BinarySearch(value As Object) As Integer
Public Function BinarySearch(item As T) As Integer

The value to look for is passed argument to the method. Here is an example:

Private Sub btnResult_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles btnResult.Click
        Dim strFind As String = txtLookFor.Text

        If ListOfNames.BinarySearch(strFind) > 0 Then
            txtResult.Text = "Found"
        Else
            txtResult.Text = "Not Found"
        End If
End Sub

To remove all items from a list at once, you can call the Clear() method of either the ArrayList or the List class. Its syntax is:

Public Overridable Sub Clear

As opposed to adding a value to a list, you may want to remove one. To perform this operation, you have various options. You can ask the compiler to look for an item in the list and if, or once, the compiler finds it, it would delete the value. To perform this type of deletion, you can call the Remove() method of either the ArrayList or the List class. Its syntax is:

Public Overridable Sub Remove(obj As Object)
Public Function Remove(item As T) As Boolean

This method accepts as argument the value that you want to delete from the list. To perform this operation, the list must not be read-only. Here is an example:

Private Sub btnDelete_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles btnDelete.Click
        ListOfNames.Remove("Ursula Morales")
        lbxNames.Items.Clear()

        For Each strName As String In ListOfNames
            lbxNames.Items.Add(strName)
        Next
End Sub

The Remove() method allows you to specify the exact value you want to delete from a list. Another option you have consists of deleting a value based on its position. This is done using the RemoveAt() method whose syntax is:

Public Overridable Sub RemoveAt(index As Integer)

With this method, the position of the item is passed as argument. Here is an example:

Private Sub btnDelete_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles btnDelete.Click
        ListOfNames.RemoveAt(1)
        lbxNames.Items.Clear()

        For Each strName As String In ListOfNames
            lbxNames.Items.Add(strName)
        Next
End Sub

If the position is not valid because either it is lower or higher than the current Count, the compiler would throw an ArgumentOutOfRangeException exception.

1. Create a Windows Application named MusicInstrumentStore3
2. Follow the instructions from the previous lesson to design the forms
3. Use the ArrayList class to create and manage the list of store items
4. Configure the application so that, if the user double-clicks an object in the Available Items list view:
   1. The Item Editor would open and display the information about the item that was clicked
   2. The Create button would display a caption as Submit
   3. The Close button would display a caption as Cancel
   4. The user can then change any detail about the item and click
   5. If the user clicks Submit, the (same) item would be updated in the database
   6. If the user clicks Cancel, the dialog box would be closed and the item would not receive any change
5. Configure the Available Items list view so that, if the user clicks an item and presses Delete:
   1. A message box would ask the user, "Are you sure you want to remove this item from the database?" and would display two buttons: Yes and No
   2. If the user clicks Yes, the item would be removed from the database
   3. If the user clicks No, nothing would happen

1. Open the CollegeParkAutoParts1 application from this lesson
2. Add a context menu for the Available Parts list view with the items: Select, Edit..., and Delete
    
   
3. Configure the context menu so that
   1. If the user clicks Select, the behavior would be the same as if the user had double-clicked the item
   2. If the user clicks Edit..., the Part Editor dialog box would display with the part in it. The user can then edit any part (year, make, model, category, part name, or unit price) except the part number. Then the user can save the changed part
   3. If the user clicks Delete, a message box would warn the user and ask for confirmation with Yes/No answers. If the user clicks Yes, the part would be deleted from the list of auto parts
4. Configure the application so that the user can open an order, add new parts to it, or delete parts from it, then save the order
5. Extend the application so that the store can also sell items that are, or are not, car-related, such as books, t-shirts, cleaning items, maintenance items (steering oils, brake oils, etc), license plates, etc. Every item in the store should have an item number. The user can enter that item number in the Part # text box and press Tab or Enter. The corresponding item would then be retrieved from the database and displayed on the form. If there is no item with that number, a message box should let the user know