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List Boxes
 

Introduction to List Boxes
 

Description

A list box presents a list of items to choose from. Each item displays on a line. The user makes a selection by clicking in the list. Once clicked, the item or line on which the mouse landed becomes highlighted, indicating that it is the current choice. Here is an example:

The Commands tab of the Customize dialog box of Microsoft Access

After an item has been selected, to make a different selection, the user would click another. The new clicked item becomes selected or highlighted; the previously selected item looses its highlighting attribute. The user can also change the selection by pressing the up or down arrow keys.

List boxes are categorized in two types: single and multi-selection. The second category allows a user to select more than one item by pressing Ctrl to select items at random or by pressing Shift to select items in a range.

One of the main reasons for using a list box is to display a list of items to the user. Sometimes the list would be very large. If the list is longer than the available client area of the control, the control would be equipped with a scroll bar that allows the user to navigate up and down to access all items of the list. You will have the option of deciding how many items to display on the list.

Practical Learning Practical Learning: Introducing List Boxes
  1. Start Microsoft Visual Basic and create a new Windows Application named MusicalInstrumentStore1
  2. In the Solution Explorer, right-click Form1.vb and click Rename
  3. Type MusicStore.vb and press Enter

Creating a List Box

To support list boxes, the .NET Framework provides the ListBox class. At design time, to add a list box to an application, from the Common Controls section of the Toolbox, click the ListBox control and click the form or the control that will host it. To programmatically create a list box, declare a variable of type ListBox, use the new operator to allocate memory it, and add it to the Controls property of its eventual parent. 

Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        Private lbxFamily As ListBox

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            lbxFamily = New ListBox()

            Controls.Add(lbxFamily)

        End Sub

    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module
Author Note In our applications, the names of the list-based controls will be in plural. This is not a rule and it is not based on any preconceived standard.
 

Practical Learning Practical Learning: Creating List Boxes
  1. Design the form as follows:
     
    Musical Instrument Shop - Form Design
     
    Control Text Name Other Properties
    GroupBox GroupBox Musical Instrument Selection    
    Label Label Categories    
    Label Label Types    
    Label Label Items    
    ListBox ListBox   lbxCategories  
    ListBox ListBox   lbxTypes  
    ListBox ListBox   lbxItems  
    GroupBox GroupBox Selected Items    
    Label Label   Part #  
    Label Label   Description  
    Label Label   Unit Price  
    Label Label   Qty  
    Label Label   Sub Total  
    TextBox TextBox   txtPartID1  
    TextBox TextBox   txtDescription1  
    TextBox TextBox 0.00 txtUnitPrice1 TextAlign: Right
    TextBox TextBox 0 txtQantity1 TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal1 TextAlign: Right
    Button Button Rmv btnRemove1  
    TextBox TextBox   txtPartID2  
    TextBox TextBox   txtDescription2  
    TextBox TextBox 0.00 txtUnitPrice2 TextAlign: Right
    TextBox TextBox   txtQuantity2 TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal2 TextAlign: Right
    Button Button Rmv btnRemove2  
    TextBox TextBox   txtPartID3  
    TextBox TextBox   txtDescription3  
    TextBox TextBox 0.00 txtUnitPrice3 TextAlign: Right
    TextBox TextBox 0 txtQuantity3 TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal3 TextAlign: Right
    Button Button Rmv btnRemove3  
    TextBox TextBox   txtPartID4  
    TextBox TextBox   txtDescription4  
    TextBox TextBox 0.00 txtUnitPrice4 TextAlign: Right
    TextBox TextBox   txtQuantity4 TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal4 TextAlign: Right
    Button Button Rmv btnRemove4  
    TextBox TextBox   txtPartID5  
    TextBox TextBox   txtDescription5  
    TextBox TextBox 0.00 txtUnitPrice5 TextAlign: Right
    TextBox TextBox 0 txtQuantity5 TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal5 TextAlign: Right
    Button Button Rmv btnRemove5  
    TextBox TextBox   txtPartID6  
    TextBox TextBox   txtDescription6  
    TextBox TextBox 0.00 txtUnitPrice6 TextAlign: Right
    TextBox TextBox 0 txtQuantity6 TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal6 TextAlign: Right
    Button Button Rmv btnRemove6  
    Button Button Close btnClose  
    Label Label   Order Total:  
    TextBox TextBox 0.00 txtTotalOrder TextAlign: Right
  2. Save the form

The Items of a List Box
 

Introduction

Like every control, when creating a list box, make sure you give it a name. Once the list box is positioned on a container, as done with other controls, you can move it by clicking and dragging the control. You can also resize it using any of the techniques we learned to add, position, move, and resize controls. If the list will cover many items, design it so its height can display 8 items at a time. Otherwise, for a list of 8 or less items, use only the necessary height that would accommodate all of the items.

Adding Items to a List Box

The most important characteristic of a list box is the list of items it contains. This list is represented by the Items property. The Items list is created and managed by a ListBox-nested class named ObjectCollection. ObjectCollection is a collection class that implements the IList, the ICollection, and the IEnumerable interfaces.

At design time, to create a list of items, access the Properties window of the list box and click the ellipsis button of the Items field. This would open the String Collection Editor:

String Collection Editor

In the empty window, you can type an item, press Enter, add another, and so on. After creating the list, you can click OK. To programmatically add an item to the list, access the Items property, call its Add() method, and pass the new item. You can do this continually for each item. Here are examples:

Public Sub InitializeComponent()

            lbxFamily = New ListBox()
            lbxFamily.Location = New Point(12, 12)

            lbxFamily.Items.Add("Son")
            lbxFamily.Items.Add("Daughter")
            lbxFamily.Items.Add("Father")
            lbxFamily.Items.Add("Mother")

            Controls.Add(lbxFamily)

End Sub

This would produce:

You can also first create an array of items and then add that array to the collection. To support this, the ObjectCollection class provides the AddRange() method. Here is an example:

Public Sub InitializeComponent()

            lbxFamily = New ListBox()
            lbxFamily.Location = New Point(12, 12)
            lbxFamily.Items.Add("Son")
            lbxFamily.Items.Add("Daughter")
            lbxFamily.Items.Add("Father")
            lbxFamily.Items.Add("Mother")

            Dim strMembers As String() = {"Niece", "Nephew", "Uncle"}
            lbxFamily.Items.AddRange(strMembers)

            Controls.Add(lbxFamily)

End Sub
 

This would produce:

If you use either the Add() or the AddRange() method to add an item or a group of items, the item or the group would be added to the end of the list, if a list exists already. To insert a new item somewhere inside of the list, call the Insert() method.

Practical Learning Practical Learning: Adding Items to a List Box
  1. On the form, click the Categories list box
  2. In the Properties window, click Items and click its ellipsis button
  3. Type Guitars and press Enter
  4. Type Bass and press Enter
  5. Complete the list to have the following items:
     
    Guitars
    Bass
    Keyboards
    Drums & Percussion
    Band & Orchestra
    Recording & Sound
    Folk Instruments
    Books & Videos
    Accessories
  6. Click OK
  7. To programmatically add items to the list boxes, on the form, double-click an unoccupied area to access its Load event and implement it as follows:
      
    Private Sub MusicStore_Load(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles MyBase.Load
        lbxTypes.Items.Add("Electric Guitars")
        lbxTypes.Items.Add("Acoustic Guitars")
        lbxTypes.Items.Add("Acoustic-Electric Guitars")
        lbxTypes.Items.Add("Amplifiers")
        lbxTypes.Items.Add("Effects")
        lbxTypes.Items.Add("Microphones")
        lbxTypes.Items.Add("Accessories")
        lbxTypes.Items.Add("Value Packages")
End Sub
  8. Execute the application to test it
  9. After using the form, close it and return your programming environment
  10. To create a class, on the main menu, click Project -> Add Class...
  11. In the Templates list, make sure Class is select.
    Set the name to PartDescription and click Add
  12. Complete the class as follows:
      
    Imports System.Net.Mail
Public Class PartDescription
    Private number As String
    Private discr As String
    Private uprice As Double

    Property PartNumber() As String
        Get
            Return number
        End Get
        Set(ByVal value As String)
            number = value
        End Set
    End Property

    Property PartName() As String
        Get
            Return discr
        End Get
        Set(ByVal value As String)
            discr = value
        End Set
    End Property

    Public Property UnitPrice() As Double
        Get
            Return uprice
        End Get
        Set(ByVal value As Double)
            uprice = value
        End Set
    End Property

    Public Sub New()
        number = ""
        discr = ""
        uprice = 0.0
    End Sub

    Public Sub New(ByVal nbr As String, _
                   ByVal name As String, _
                   ByVal price As Double)
        number = nbr
        discr = name
        uprice = price
    End Sub

    Public Overrides Function ToString() As String
        Return PartNumber & " " & _
               PartName & " " & _
               UnitPrice.ToString()
    End Function

End Class
  13. Access the MusicStore.vb file and create a few arrays as follows:
      
    Public Class MusicStore

    Private CatBass() As String
    Private CatKeyboard() As String
    Private CatDrums() As String
    Private CatBand() As String
    Private CatAccessories() As String

    Private ElectricGuitars() As PartDescription
    Private AcousticGuitars() As PartDescription
    Private ElectricBasses() As PartDescription
    Private AcousElectBasses() As PartDescription
    Private Pianos() As PartDescription
    Private Synthetizers() As PartDescription
    Private Books() As PartDescription
    Private Cables() As PartDescription

    Private Sub MusicStore_Load(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles MyBase.Load
        lbxTypes.Items.Add("Electric Guitars")
        lbxTypes.Items.Add("Acoustic Guitars")
        lbxTypes.Items.Add("Acoustic-Electric Guitars")
        lbxTypes.Items.Add("Amplifiers")
        lbxTypes.Items.Add("Effects")
        lbxTypes.Items.Add("Microphones")
        lbxTypes.Items.Add("Accessories")
        lbxTypes.Items.Add("Value Packages")

        CatBass = New String() { _
            "Electric Bass", "Acoustic-Electric Bass", _
            "Amplifiers", "Effects", "Accessories"}

        CatKeyboard = New String() { _
            "Pianos", "Organs", "Synthesizers", _
            "Portable", "Workstations", "Arrangers", _
            "Stands", "Amps", "Pedals", "Accessories"}

        CatDrums = New String() { _
                  "Acoustic Drums", "Cymbals", _
                  "Electronic Percussion", "World Percussion"}

        CatBand = New String() { _
                   "Trumpets", "Trombones", "Saxophones", _
                   "Clarinets", "Flutes", "Baritones", "Tubas", _
                   "Oboes", "Recorders", "Accessories"}

        CatAccessories = New String() { _
                  "Headphones", "Strings", "Slides", "Metronomes", _
                  "Tuners", "Music Stands", "Cases", "Cables", _
                  "Hearing Protection", "Electric Guitar Bags", _
                  "Guitar Pedals", "Cleaning/Care"}

        ElectricGuitars = New PartDescription() _
        { _
            New PartDescription("293027", _
                                "Gibson Les Paul Vintage Solid Guitar", _
                                850.75), _
            New PartDescription("972355", _
                        "Fender Standard Stratocaster Electric Guitar", _
                        435.95), _
            New PartDescription("390057", _
             "Gibson Les Paul Standard Left-Handed 50s Neck Electric Guitar", _
            2400.0), _
            New PartDescription("297548", _
                "Schecter C-1 Hellraiser Electric Guitar", _
                649.95), _
            New PartDescription("284704", _
            "Gretsch Guitars G5120 Electromatic Hollowbody Electric Guitar", _
            595.95), _
            New PartDescription("293472", _
            "Rickenbacker 360 12-String Electric Guitar", _
            2195.95), _
            New PartDescription("208476", _
            "Steinberger Synapse ST-2FPA TranScale Custom Electric Guitar", _
            1045.5), _
            New PartDescription("253463", _
            "Gibson EDS 1275 Double-Neck Electric Guitar", _
            3050.25), _
            New PartDescription("225747", _
            "Fender American Stratocaster Left-Handed Electric Guitar", _
            950.5), _
            New PartDescription("274875", _
            "Epiphone Dot Studio Semi-Hollow Electric Guitar", _
            295.25) _
        }

        AcousticGuitars = New PartDescription() _
        { _
            New PartDescription("224885", _
            "Epiphone Hummingbird Acoustic Guitar", 245.55), _
            New PartDescription("283407", _
            "Dean V Coustic Thin Body Acoustic-Electric Guitar", 205.5), _
            New PartDescription("275111", _
            "Yamaha FG720S 12-String Acoustic Guitar", 325.55), _
            New PartDescription("249036", _
            "Rogue RA-100D Dreadnought Acoustic Guitar", 82.95), _
            New PartDescription("285507", _
            "Alvarez RD8 Regent Series Dreadnought Acoustic Guitar", 220.5), _
            New PartDescription("283746", _
            "Epiphone EJ-200 Acoustic Guitar", 350.5) _
        }

        ElectricBasses = New PartDescription() _
              { _
                  New PartDescription("248780", _
                  "Epiphone Thunderbird IV Bass", 325.5), _
                  New PartDescription("203487", _
                  "Squier® Vintage Modified '70s Jazz Bass", 305.95), _
                  New PartDescription("204633", _
                  "Fender Standard Precision Bass", 450.75), _
                  New PartDescription("297548", _
                  "Music Man StingRay 5-String Bass Guitar", 1485.95) _
              }

        AcousElectBasses = New PartDescription() _
             { _
                 New PartDescription("248780", _
                 "Ibanez AEB10E Acoustic-Electric Bass Guitar with Onboard Tuner", _
                 335.5), _
                 New PartDescription("203487", _
                 "Dean Playmate EABC 5-String Cutaway Acoustic-Electric Bass", _
                 285.95), _
                 New PartDescription("204633", _
                 "Fender BG-32 Acoustic/Electric Bass Guitar", _
                 495.75), _
                 New PartDescription("634974", _
                 "Gibson Thunderbird IV Bass", 1500.0), _
                 New PartDescription("674950", _
                 "Rogue VB-100 Violin Bass", 255.95), _
                 New PartDescription("634742", _
                 "Squier Standard P Bass 4-String Bass", _
                 220.75), _
                 New PartDescription("637904", _
                 "Peavey Millennium BXP 4-String Bass", 210.95) _
             }

        Pianos = New PartDescription() _
              { _
                  New PartDescription("584603", _
                  "Williams ETUDE Console Piano", 450.95), _
                  New PartDescription("504724", _
                  "Rolan EP-760C Digital Piano w/Stand", 650.95) _
              }

        Synthetizers = New PartDescription() _
              { _
                  New PartDescription("582970", _
                  "Alesis ION 49-Key 1K DSP Synthesizer", 750.5), _
                  New PartDescription("524885", _
                  "Korg MicroKORG Synthesizer/Vocoder", 350.75), _
                  New PartDescription("549085", _
                  "Yamaha YDP223 Digital Piano", 1450.0), _
                  New PartDescription("529307", _
                  "Access Virus kc 5-Octave Synth", 1915.55) _
              }

        Dim Books = New PartDescription() _
               { _
                   New PartDescription("883670", _
                   "Alfred Guitar for the Absolute Beginner", _
                   16.55), _
                   New PartDescription("837654", _
                   "Hal Leonard Guitar Tab White Pages", 20.95), _
                   New PartDescription("843047", _
                   "Carl Fischer Guitar Grimoire Progressions and Improvisation", _
                   24.75), _
                   New PartDescription("845716", _
                   "Bill Edwards Publishing Fretboard logic Spc Ed.", _
                   17.95), _
                   New PartDescription("833427", _
                   "Walrus Productions Guitar Chord Poster", 6.85) _
               }

        Cables = New PartDescription() _
              { _
                  New PartDescription("188370", _
                  "Musician's Friend Professional Cable", _
                  4.55), _
                  New PartDescription("183614", _
                  "Monster Cable S-100 Straight Cable", 20.95), _
                  New PartDescription("143047", _
                  "Hosa TRS-TRS Stereo 1/4"" Cable", 4.65), _
                  New PartDescription("145716", _
                  "Mogami Silver Series Cable", 12.95) _
              }
    End Sub
End Class
  14. Save all

Selecting an Item in a List Box

To an item from a list box, the user must locate and click the desired item. That item is said to have been selected. To programmatically select an item, you can assign the index of the desired item to the ListBox.SelectedIndex property. The indices of the items of a list box are stored in a zero-based array. This means that the first item has an index of 0, the second has an index of 1, and so on. Here is an example that will select the fourth item of the list:

Public Sub InitializeComponent()

            lbxFamily = New ListBox()
            lbxFamily.Location = New Point(12, 12)
            lbxFamily.Items.Add("Son")
            lbxFamily.Items.Add("Daughter")
            lbxFamily.Items.Add("Father")
            lbxFamily.Items.Add("Mother")

            Dim strMembers As String() = {"Niece", "Nephew", "Uncle"}
            lbxFamily.Items.AddRange(strMembers)

            lbxFamily.SelectedIndex = 3

            Controls.Add(lbxFamily)

End Sub

This would produce:

Selected Item

After an item has been selected, to find out the index of the item that is currently selected, get the value of the ListBox.SelectedIndex property.

To select an item, the user can click it in the list box. When an item has been clicked, the list box fires a SelectedIndexChanged event. Because selecting an item is the most regularly performed operation on a list box, SelectedIndexChanged is the default event of a list box. This event is of type EventArgs which means that it does not provide any significant information other than to let you know that an item has been selected. Nonetheless, this event allows you to easily check if an item has been selected and what item has been selected.
To fire a SelectedIndexChanged event and to test what item has been selected in the list, you can double-click the list box.

The ListBox.SelectedIndex property allows you either to select an item or to find out what item is selected, using its index, that is, the numeric position of the item in the list. If you know the identity, such as the name, of the item you want to select, or if you want to identify the selected item based on its name, you can use the ListBox.SelectedItem property instead. This member identifies the item instead of locating it.

By default, the user can select only one item in the list. If you want the user to be able to select more than one item, change the value of the SelectionMode property. This property is based on the SelectionMode enumeration. After the user has selected more than one item, to get the indexes of the items that are selected, you can access the ListBox.SelectedIndices property which holds that list.

Practical Learning Practical Learning: Selecting an Item From a List Box
  1. In the Class Name combo box, select lbxCategories
  2. In the Method Name combo box, select SelectedIndexChanged and implement the event as follows:
      
    Private Sub lbxCategories_SelectedIndexChanged(ByVal sender As Object, _
                                ByVal e As System.EventArgs) _
                                Handles lbxCategories.SelectedIndexChanged
        If lbxCategories.SelectedItem = CType("Guitars", Object) Then
            lbxTypes.Items.Add("Electric Guitars")
            lbxTypes.Items.Add("Acoustic Guitars")
            lbxTypes.Items.Add("Acoustic-Electric Guitars")
            lbxTypes.Items.Add("Amplifiers")
            lbxTypes.Items.Add("Effects")
            lbxTypes.Items.Add("Microphones")
            lbxTypes.Items.Add("Accessories")
            lbxTypes.Items.Add("Value Packages")
        ElseIf lbxCategories.SelectedItem = CType("Bass", Object) Then
            lbxTypes.Items.AddRange(CatBass)
        ElseIf lbxCategories.SelectedItem = CType("Keyboards", Object) Then
            lbxTypes.Items.AddRange(CatKeyboard)
        ElseIf lbxCategories.SelectedItem = CType("Drums & Percussion", Object) Then
            lbxTypes.Items.AddRange(CatDrums)
        ElseIf lbxCategories.SelectedItem = CType("Band & Orchestra", Object) Then
            lbxTypes.Items.AddRange(CatBand)
        ElseIf lbxCategories.SelectedItem = CType("Books & Videos", Object) Then
            lbxTypes.Items.Add("Books")
            lbxTypes.Items.Add("DVDs")
        ElseIf lbxCategories.SelectedItem = CType("Accessories", Object) Then
            lbxTypes.Items.AddRange(CatAccessories)
        End If
End Sub
  3. In the Class Name combo box, select lbxTypes
  4. In the Method Name combo box, select SelectedIndexChanged and implement the event as follows:
      
    Private Sub lbxTypes_SelectedIndexChanged(ByVal sender As Object, _
                                              ByVal e As System.EventArgs) _
                                              Handles lbxTypes.SelectedIndexChanged
        If lbxTypes.SelectedItem = CType("Electric Guitars", Object) Then
            For Each part As PartDescription In ElectricGuitars
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Acoustic Guitars", Object) Then
            For Each part As PartDescription In AcousticGuitars
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Electric Bass", Object) Then
            For Each part As PartDescription In ElectricBasses
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Acoustic-Electric Bass", Object) Then
            For Each part As PartDescription In AcousElectBasses
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Pianos", Object) Then
            For Each part As PartDescription In Pianos
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Synthesizers", Object) Then
            For Each part As PartDescription In Synthetizers
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Books", Object) Then
            For Each part As PartDescription In Books
                lbxItems.Items.Add(part)
            Next
        ElseIf lbxTypes.SelectedItem = CType("Cables", Object) Then
            For Each part As PartDescription In Cables
                lbxItems.Items.Add(part)
            Next
        End If
End Sub
  5. Execute the application to test it
     
    Musical Instrument Store
  6. After using the form, close it and return to your programming environment
  7. In the Class Name combo box, select lbxItems
  8. In the Method Name combo box, select DoubleClick field and make the following changes:
      
    Private Sub CalculateTotalOrder()
        Dim SubTotal1 As Double
        Dim SubTotal2 As Double
        Dim SubTotal3 As Double
        Dim SubTotal4 As Double
        Dim SubTotal5 As Double
        Dim SubTotal6 As Double
        Dim OrderTotal As Double

        Try
            SubTotal1 = CDbl(txtSubTotal1.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            SubTotal2 = CDbl(txtSubTotal2.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            SubTotal3 = CDbl(txtSubTotal3.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            SubTotal4 = CDbl(txtSubTotal4.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            SubTotal5 = CDbl(txtSubTotal5.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            SubTotal6 = CDbl(txtSubTotal6.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        ' Calculate the total value of the sub totals
        OrderTotal = SubTotal1 + SubTotal2 + SubTotal3 + _
        SubTotal4 + SubTotal5 + SubTotal6

        ' Display the total order in the appropriate text box
        txtTotalOrder.Text = OrderTotal.ToString()
End Sub

Private Sub lbxItems_DoubleClick(ByVal sender As Object, _
                                     ByVal e As System.EventArgs) _
                                     Handles lbxItems.DoubleClick
        ' We will use a PartDescription object to identify the selected item
        Dim part As PartDescription = New PartDescription()

        ' When the user double-clicks an item, retrieve it as
        ' a PartDescription object
        part = CType(lbxItems.SelectedItem, PartDescription)

        ' If the first Part # box is empty, then use it
        If txtPartID1.Text = "" Then
            ' Display the item number in the Part # text box
            txtPartID1.Text = part.PartNumber
            ' Display the name of the selected item in 
            ' the current Description text box
            txtDescription1.Text = part.PartName
            ' Display the unit price of this item in
            ' the corresponding Unit Price text box
            txtUnitPrice1.Text = part.UnitPrice.ToString()

            ' Enable the Remove button of the current item
            btnRemove1.Enabled = True

            ' Since an item was selected, set its quantity to 1
            txtQuantity1.Text = "1"
            ' Calculate the sub total of the current item item
            txtSubTotal1.Text = (part.UnitPrice * 1).ToString()
            ' Give focus to the Qty text box of the current item
            txtQuantity1.Focus()
            ' If the previous Part # text box is not empty, then use the next one
        ElseIf txtPartID2.Text = "" Then
            txtPartID2.Text = part.PartNumber
            txtDescription2.Text = part.PartName
            txtUnitPrice2.Text = part.UnitPrice.ToString()

            ' Enable the Remove button of the current item
            btnRemove2.Enabled = True

            txtQuantity2.Text = "1"
            txtSubTotal2.Text = (part.UnitPrice * 1).ToString()
            txtQuantity2.Focus()
        ElseIf txtPartID3.Text = "" Then
            txtPartID3.Text = part.PartNumber
            txtDescription3.Text = part.PartName
            txtUnitPrice3.Text = part.UnitPrice.ToString()

            ' Enable the Remove button of the current item
            btnRemove3.Enabled = True

            txtQuantity3.Text = "1"
            txtSubTotal3.Text = (part.UnitPrice * 1).ToString()
            txtQuantity3.Focus()
        ElseIf txtPartID4.Text = "" Then
            txtPartID4.Text = part.PartNumber
            txtDescription4.Text = part.PartName
            txtUnitPrice4.Text = part.UnitPrice.ToString()

            ' Enable the Remove button of the current item
            btnRemove4.Enabled = True

            txtQuantity4.Text = "1"
            txtSubTotal4.Text = (part.UnitPrice * 1).ToString()
            txtQuantity4.Focus()
        ElseIf txtPartID5.Text = "" Then
            txtPartID5.Text = part.PartNumber
            txtDescription5.Text = part.PartName
            txtUnitPrice5.Text = part.UnitPrice.ToString()

            ' Enable the Remove button of the current item
            btnRemove5.Enabled = True

            txtQuantity5.Text = "1"
            txtSubTotal5.Text = (part.UnitPrice * 1).ToString()
            txtQuantity5.Focus()
        ElseIf txtPartID6.Text = "" Then
            txtPartID6.Text = part.PartNumber
            txtDescription6.Text = part.PartName
            txtUnitPrice6.Text = part.UnitPrice.ToString()

            ' Enable the Remove button of the current item
            btnRemove6.Enabled = True

            txtQuantity6.Text = "1"
            txtSubTotal6.Text = (part.UnitPrice * 1).ToString()
            txtQuantity6.Focus()
            ' If all Part # text boxes are filled, don't do anything
        Else
            Exit Sub
        End If

        ' Calculate the current total order and update the order
        CalculateTotalOrder()
End Sub
  9. Under the above procedure, create a new procedure as follows:
      
    Private Sub TextBoxLeaving(ByVal sender As Object, _
                               ByVal e As System.EventArgs) _
                               Handles txtUnitPrice1.Leave, txtQuantity1.Leave, _
                                       txtUnitPrice2.Leave, txtQuantity2.Leave, _
                                       txtUnitPrice3.Leave, txtQuantity3.Leave, _
                                       txtUnitPrice4.Leave, txtQuantity4.Leave, _
                                       txtUnitPrice5.Leave, txtQuantity5.Leave, _
                                       txtUnitPrice6.Leave, txtQuantity6.Leave
        Dim Quantity1 As Integer, Quantity2 As Integer
        Dim Quantity3 As Integer, Quantity4 As Integer
        Dim Quantity5 As Integer, Quantity6 As Integer
        Dim UnitPrice1 As Double, UnitPrice2 As Double
        Dim UnitPrice3 As Double, UnitPrice4 As Double
        Dim UnitPrice5 As Double, UnitPrice6 As Double
        Dim SubTotal1 As Double, SubTotal2 As Double
        Dim SubTotal3 As Double, SubTotal4 As Double
        Dim SubTotal5 As Double, SubTotal6 As Double

        ' Get the quantity of the current item
        Try
            Quantity1 = CInt(txtQuantity1.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        ' Get the unit price of the current item
        Try
            UnitPrice1 = CDbl(txtUnitPrice1.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            Quantity2 = CInt(txtQuantity2.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            UnitPrice2 = CDbl(txtUnitPrice2.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            Quantity3 = CInt(txtQuantity3.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            UnitPrice3 = CDbl(txtUnitPrice3.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            Quantity4 = CInt(txtQuantity4.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            UnitPrice4 = CDbl(txtUnitPrice4.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            Quantity5 = CInt(txtQuantity5.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            UnitPrice5 = CDbl(txtUnitPrice5.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            Quantity6 = CInt(txtQuantity6.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        Try
            UnitPrice6 = CDbl(txtUnitPrice6.Text)
        Catch ex As Exception
            MsgBox("Invalid Value")
        End Try

        ' Calculate the sub totals
        SubTotal1 = Quantity1 * UnitPrice1
        SubTotal2 = Quantity2 * UnitPrice2
        SubTotal3 = Quantity3 * UnitPrice3
        SubTotal4 = Quantity4 * UnitPrice4
        SubTotal5 = Quantity5 * UnitPrice5
        SubTotal6 = Quantity6 * UnitPrice6

        ' Display the sub totals in the corresponding text boxes
        txtSubTotal1.Text = CStr(SubTotal1)
        txtSubTotal2.Text = CStr(SubTotal2)
        txtSubTotal3.Text = CStr(SubTotal3)
        txtSubTotal4.Text = CStr(SubTotal4)
        txtSubTotal5.Text = CStr(SubTotal5)
        txtSubTotal6.Text = CStr(SubTotal6)

        ' Update the order
        CalculateTotalOrder()
End Sub
  10. In the Class Name combo box, select btnRemove1
  11. In the Method Name combo box, select Click and implement the event as follows:
      
    Private Sub btnRemove1_Click(ByVal sender As Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles btnRemove1.Click
        txtPartID1.Text = ""
        txtDescription1.Text = ""
        txtUnitPrice1.Text = "0.00"
        txtQuantity1.Text = "0"
        txtSubTotal1.Text = "0.00"
        btnRemove1.Enabled = False
End Sub
  12. In the Class Name combo box, select btnRemove2
  13. In the Method Name combo box, select Click and implement the event as follows:
      
    Private Sub btnRemove2_Click(ByVal sender As Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles btnRemove2.Click
        txtPartID2.Text = ""
        txtDescription2.Text = ""
        txtUnitPrice2.Text = "0.00"
        txtQuantity2.Text = "0"
        txtSubTotal2.Text = "0.00"
        btnRemove2.Enabled = False
End Sub
  14. In the Class Name combo box, select btnRemove3
  15. In the Method Name combo box, select Click and implement the event as follows:
      
    Private Sub btnRemove3_Click(ByVal sender As Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles btnRemove3.Click
        txtPartID3.Text = ""
        txtDescription3.Text = ""
        txtUnitPrice3.Text = "0.00"
        txtQuantity3.Text = "0"
        txtSubTotal3.Text = "0.00"
        btnRemove3.Enabled = False
End Sub
  16. In the Class Name combo box, select btnRemove4
  17. In the Method Name combo box, select Click and implement the event as follows:
      
    Private Sub btnRemove4_Click(ByVal sender As Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles btnRemove4.Click
        txtPartID4.Text = ""
        txtDescription4.Text = ""
        txtUnitPrice4.Text = "0.00"
        txtQuantity4.Text = "0"
        txtSubTotal4.Text = "0.00"
        btnRemove4.Enabled = False
End Sub
  18. In the Class Name combo box, select btnRemove5
  19. In the Method Name combo box, select Click and implement the event as follows:
      
    Private Sub btnRemove5_Click(ByVal sender As Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles btnRemove5.Click
        txtPartID5.Text = ""
        txtDescription5.Text = ""
        txtUnitPrice5.Text = "0.00"
        txtQuantity5.Text = "0"
        txtSubTotal5.Text = "0.00"
        btnRemove5.Enabled = False
End Sub
  20. In the Class Name combo box, select btnRemove6
  21. In the Method Name combo box, select Click and implement the event as follows:
      
    Private Sub btnRemove6_Click(ByVal sender As Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles btnRemove6.Click
        txtPartID6.Text = ""
        txtDescription6.Text = ""
        txtUnitPrice6.Text = "0.00"
        txtQuantity6.Text = "0"
        txtSubTotal6.Text = "0.00"
        btnRemove6.Enabled = False
End Sub
  22. In the Class Name combo box, select btnClose
  23. 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
  24. Execute the application to test it

Removing Items From a List Box

If you have an undesired item in a list box, you can remove it. To To support this operation, the ObjectCollection class provides the Remove() method. When calling it, pass the name of the item as argument. This means that you must know the item you are trying to delete. If you call this method, the compiler would look for the item in the list. If the item is found, it would be deleted.

Instead of removing an item by its name or identification, you can use its position. To do that, you can call the RemoveAt() method and pass the zero-based index of the undesired item. If the index is valid, the item would be deleted from the list.

To remove all items from the list, you can call the Clear() method.

Practical Learning Practical Learning: Removing Items From a List Box
  1. Change the SelectedIndex events of the Types and the Items list boxes as follows:
      
    Private Sub lbxCategories_SelectedIndexChanged(ByVal sender As Object, _
                                ByVal e As System.EventArgs) _
                                Handles lbxCategories.SelectedIndexChanged

        lbxTypes.Items.Clear()
        lbxItems.Items.Clear()

        . . . No Change

End Sub

Private Sub lbxTypes_SelectedIndexChanged(ByVal sender As Object, _
                                              ByVal e As System.EventArgs) _
                                              Handles lbxTypes.SelectedIndexChanged
        lbxItems.Items.Clear()

        If lbxTypes.SelectedItem = CType("Electric Guitars", Object) Then
            For Each part As PartDescription In ElectricGuitars
                lbxItems.Items.Add(part)
            Next
        . . . No Change
End Sub
  2. Execute the application to test it. Here is an example:
     
    Musical Instrument Shop - Result
  3. Close the form and return to your programming environment

Sorting a List Box

After creating the list, by default, each item assumes the position it received when it was added. If you want, you can rearrange them in ascending order. To do this, set the ListBox.Sorted Boolean property to True. If you create an unsorted list, then at one time get it sorted (for example, you can give the user the ability to sort the list, by clicking a button), the list would be sorted. If an item is added to the sorted list, the compiler would automatically insert it to the right position following the alphabetical, ascending or chronological order. If at another time you allow the user to “unsort” the list, the list would keep its current order. If another item is added when the list is not sorted, the item would be positioned at the end of the list. If you want the list to have its original state, you would have to reset it through code.

Practical Learning Practical Learning: Sorting a List Box
  1. On the form, click the Items list box
  2. In the Properties window, double-click Sorted to set its value to True

Lesson's Summary
 

Topics
  • List Box
  • Identifying the Index of a Selected Item

Exercises
  1. Create an application named WorldStatistics1
  2. Add two list boxes so that, when a continent is selected in the first combo box, the second list box gets filled with the countries from that continent
  3. Add a third list box so that, when a country is selected from the second list box, the list of its states or provinces is filled in the third list box
 
 
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