Dictionary-Based Collections

Introduction to Dictionaries

Description

A dictionary is a list of items with the following two rules:

• Each item is a combination of a key and a value. An item can be made of three parts: a key, a value, and a correspondence between them. The correspondence can be represented by the assignment operator: Key=Value. In some environments, the = operator is used. In some others, the : operator is used. Yet in some others, there is no actual operator that joins both sides but you must know that the key and the value go in pair
• As each item is a combination of a key and a value, each key must be unique. The list of items in the dictionary can be very huge, sometimes in the thousands or even millions. Among the items, each key must be distinct from any other key in the dictionary

In some cases, in addition to these two rules, the items should - in some cases must - be ordered. To order the items, the keys are used. Because in most cases a dictionary is made of words, the keys are ordered in alphabetical order. A dictionary can also be made of items whose keys are date values. In this case, the items would be ordered in chronological order.

There are various kinds of dictionary types of list used in daily life. The word "dictionary" here does not imply the traditional dictionary that holds the words and their meanings in the English language. The concept is applied in various scenarios.

1. Start Microsoft Visual Basic and create a new Windows Forms Application named BethesdaCarRental1
2. To add a new form to the project, in the Solution Explorer, right-click BethesdaCarRental1 -> Add -> Windows Form...
3. Set the Name to RentalRates and press Enter
4. Add a ListView to the form and create its Columns as follows:
    

   (Name)	Text	TextAlign	Width
   colCategory	Category		90
   colDaily	Daily	Right
   colWeekly	Weekly	Right
   colMonthly	Monthly	Right
   colWeekend	Weekend	Right

5. Create its Items as follows:
    

   ListViewItem	SubItems	SubItems	SubItems	SubItems
   	Text	Text	Text	Text
   Economy	35.95	32.75	28.95	24.95
   Compact	39.95	35.75	32.95	28.95
   Standard	45.95	39.75	35.95	32.95
   Full Size	49.95	42.75	38.95	35.95
   Mini Van	55.95	50.75	45.95	42.95
   SUV	55.95	50.75	45.95	42.95
   Truck	42.75	38.75	35.95	32.95
   Van	69.95	62.75	55.95	52.95

6. Complete the design of the form as follows:
    
   
7. To add a new form to the application, in the Solution Explorer, right-click BethesdaCarRental1 -> Add -> Windows Form...
8. Set the Name to Employees and click Add
9. From the Toolbox, add a ListView to the form
10. While the new list view is still selected, in the Properties window, click the ellipsis button of the Columns field and create the columns as follows:
     

    (Name)	Text	TextAlign	Width
    colEmployeeNumber	Empl #		45
    colFirstName	First Name		65
    colLastName	Last Name		65
    colFullName	Full Name		140
    colTitle	Title		120
    colHourlySalary	Hourly Salary	Right	75

11. Design the form as follows: 
     

    Control Text Name Other Properties ListView   lvwEmployees Anchor: Top, Bottom, Left, Right FullRowSelect: True GridLines: True View: Details Button New Employee... btnNewEmployee   Button Close btnClose

12. To add another form to the application, in the Solution Explorer, right- click BethesdaCarRental1 -> Add -> Windows Form...
13. Set the Name to EmployeeEditor and click Add
14. Design the form as follows: 
     

    Control Text Name Properties Label &Employee #:     MaskedTextBox   txtEmployeeNumber Mask: 00-000 Modifiers: public Label First Name:     TextBox   txtFirstName Modifiers: public Label Last Name:     TextBox   txtLastName Modifiers: public Label Full Name:     TextBox   txtFullName Enabled: False Modifiers: public Label Title:     TextBox   txtTitle Modifiers: public Label Hourly Salary:     TextBox   txtHourlySalary Modifiers: public TextAlign: Right Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel Form     AcceptButton: btnOK CancelButton: btnCancel FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

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

    REM This code is used to create and display the customer's full name Private Sub txtLastName_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtLastName.Leave Dim strFirstName As String = txtFirstName.Text Dim strLastName As String = txtLastName.Text Dim strFullName As String If strFirstName.Length = 0 Then strFullName = strLastName Else strFullName = strLastName & ", " & strFirstName End If txtFullName.Text = strFullName End Sub

18. To add a new class to the project, on the main menu, click Project -> Add Class...
19. Set the Class Name to Employee and click Add
20. Change the Employee.vb file as follows:
     

    <Serializable()> Public Class Employee Public FirstName As String Public LastName As String Public Title As String Public HourlySalary As Double Public ReadOnly Property FullName() Get Return LastName & ", " & FirstName End Get End Property REM This default constructor says that REM the employee is not defined Public Sub New() FirstName = "Unknown" LastName = "Unknown" Title = "N/A" HourlySalary = 0.0 End Sub REM This constructor completely defines an employee Public Sub New(ByVal fname As String, ByVal lname As String, _ ByVal title As String, ByVal salary As Double) FirstName = fname LastName = lname Title = Title HourlySalary = salary End Sub End Class

21. To add a new form to the application, on the main menu, click Project -> Add Windows Forms
22. Set the Name to Customers and press Enter
23. From the Toolbox, add a ListView to the form
24. While the new list view is still selected, in the Properties window, click the ellipsis button of the Columns field and create the columns as follows:
     

    (Name)	Text	Width
    colDrvLicNbr	Driver's Lic. #	100
    colFullName	Full Name	100
    colAddress	Address	160
    colCity	City	100
    colState	State	38
    colZIPCode	ZIP Code

25. Design the form as follows: 
     

    Control Text Name Other Properties ListView   lvwCustomers View: Details GridLines: True FullRowSelect: True Button New Customer... btnNewCustomer   Button Close btnClose

26. To add another form to the application, on the main menu, click Project -> Add Windows Forms
27. Set the Name to CustomerEditor and click Add
28. Design the form as follows: 
     

    Control Text Name Properties Label Driver's Lic. #:     TextBox   txtDrvLicNbr Modifiers: Public Label State:     ComboBox   cbxStates Modifiers: Public Items: AL, AK, AZ, AR, CA, CO, CT, DE, DC, FL, GA, HI, ID, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, MT, NE, NV, NH, NJ, NM, NY, NC, ND, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VT, VA, WA, WV, WI, WY Label Full Name:     TextBox   txtFullName Modifiers: Public Label Address:     TextBox   txtAddress Modifiers: Public Label City:     TextBox   txtCity Modifiers: Public Label ZIP Code:     TextBox   txtZIPCode Modifiers: Public Button OK btnOK DialogResult: OK Button Close btnCancel DialogResult: Cancel Form     AcceptButton: btnOK CancelButton: btnCancel FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

29. To add a new class to the project, on the main menu, click Project -> Add Class...
30. Set the Class Name to Customer and click Finish
31. Change the Customer.vb file as follows:
     

    <Serializable()> Public Class Customer Public FullName As String Public Address As String Public City As String Public State As String Public ZIPCode As String Public Sub New() FullName = "" Address = "" City = "" State = "" ZIPCode = "" End Sub REM This constructor defines a customer Public Sub New(ByVal fName As String, _ ByVal adr As String, ByVal ct As String, _ ByVal ste As String, ByVal zip As String) FullName = fName Address = adr City = ct State = ste ZIPCode = zip End Sub End Class

32. Save all
33. Copy the following pictures to any folder somewhere on your computer (this is simply an example of preparing the pictures of cars you would include in your database application):
     

    BMW: 335i	Chevrolet Avalanche
    Honda Accord	Mazda Miata
    Chevrolet Aveo	Ford E150XL
    Buick Lacrosse	Honda Civic
    Ford F-150	Mazda Mazda5
    Volvo S40	Land Rover LR3

34. Return to your programming environment
35. To add a new form to the application, in the Solution Explorer, right-click BethesdaCarRental1 -> Add -> Windows Forms
36. Set the Name to CarEditor and click Add
37. Design the form as follows: 
     

    Control Text Name Other Properties Label Text #     TextBox   txtTagNumber   Label Make:     TextBox   txtMake   Label Model:     TextBox   txtModel   Label Year:     TextBox   txtYear   Label Category:     ComboBox   cboCategories DropDownStyle: DropDownList Items: Economy Compact Standard Full Size Mini Van SUV Truck Van PictureBox   pbxCar SizeMode: Zoom CheckBox CD Player chkCDPlayer CheckAlign: MiddleRight CheckBox DVD Player chkDVDPlayer CheckAlign: MiddleRight Button Select Car Picture... btnSelectPicture   CheckBox Available chkAvailable CheckAlign: MiddleRight Label Picture Name lblPictureName   Button Submit btnSubmit   Button Close btnClose DialogResult: Cancel OpenFileDialog (Name): dlgOpen Title: Select Item Picture DefaultExt: jpg Filter: JPEG Files (*.jpg,*.jpeg)|*.jpg|GIF Files (*.gif)|*.gif|Bitmap Files (*.bmp)|*.bmp|PNG Files (*.png)|*.png Form     FormBorderStyle: FixedDialog MaximizeBox: False MinimizeBox: False ShowInTaskbar: False

38. Double-click the Select Car Picture button and implement its event as follows:
     

    Private Sub btnSelectPicture_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnSelectPicture.Click If dlgPicture.ShowDialog() = DialogResult.OK Then lblPictureName.Text = dlgPicture.FileName pbxCar.Image = Image.FromFile(lblPictureName.Text) End If End Sub

39. To add a new class to the project, on the main menu, click Project -> Add Class...
40. Set the Class Name to Car and click Add
41. Change the file as follows:
     

    <Serializable()> Public Class Car Public Make As String Public Model As String Public Year As Integer Public Category As String Public HasCDPlayer As Boolean Public HasDVDPlayer As Boolean Public IsAvailable As Boolean Public Sub New() Make = "" Model = "" Year = 0 Category = "" HasCDPlayer = False HasDVDPlayer = False IsAvailable = False End Sub Public Sub New(ByVal mk As String, ByVal mdl As String, _ ByVal yr As Integer, ByVal cat As String, _ ByVal cd As Boolean, ByVal dvd As Boolean, _ ByVal avl As Boolean) Make = mk Model = mdl Year = yr Category = cat HasCDPlayer = cd HasDVDPlayer = dvd IsAvailable = avl End Sub End Class

42. To add a new class to the project, on the main menu, click Project -> Add Class...
43. Set the Class Name to RentalOrder and press Enter
44. Access the RentalOrder.vb file and change it as follows:
     

    <Serializable()> Public Class RentalOrder Public EmployeeNumber As String REM The following flag will allow us to update/know whether REM * The car is currently being used by the customer. REM That is, if the car has been picked up by the customer REM * The customer has brought the car back Public OrderStatus As String REM Because every car has a tag number REM and that tag number will not change REM during the lifetime of a car (while the car remains with our REM car rental company, we will REM use only the tag number here. REM The other pieces of information will REM be retrieved from the list of cars Public CarTagNumber As String REM We will identify the customer by the number REM and the name on his or her driver's license Public CustomerDrvLicNbr As String Public CustomerName As String REM Although he or she may keep the same driver's REM license number for a lifetime, a customer who REM rents cars at different times with this company REM over months or years may have different addresses. REM Therefore, although we will primarily retrieve the REM customer's address from the list of customers, REM we will give the clerk the ability to change this REM information on a rental order. This means that the REM same customer could have different information on REM different rental orders. REM For this reason, each rental order will its own set REM of these pieces of information Public CustomerAddress As String Public CustomerCity As String Public CustomerState As String Public CustomerZIPCode As String Public CarCondition As String Public TankLevel As String REM This information will be entered when the car is being rented Public MileageStart As Integer REM This information will be entered when the car is brought back Public MileageEnd As Integer REM This information will be entered when the car is being rented Public DateStart As DateTime REM This information will be entered when the car is brought back Public DateEnd As DateTime Public Days As Integer REM This information will be entered when the car is being rented Public RateApplied As Double REM This calculation should occur when the car is brought back Public SubTotal As Double Public TaxRate As Double Public TaxAmount As Double Public OrderTotal As Double End Class

45. To add a new form to the project, in the Solution Explorer, right-click BethesdaCarRenat1 -> Add -> Windows Form...
46. Set the Name to OrderProcessing and press Enter
47. Design the form as follows:
     

    Control Text Name Other Properties Label Processed By:   AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft Label Employee #:     MaskedTextBox   txtEmployeeNumber Mask: 00-000 Label Employee Name:     TextBox   txtEmployeeName   Label Processed For   AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft Label Driver's Lic #:     TextBox   txtDrvLicNumber   Label Cust Name:     TextBox   txtCustomerName   Label Address:     TextBox   txtCustomerAddress   Label City:     TextBox   txtCustomerCity   Label State:     ComboBox   cbxCustomerStates DropDownStyle: DropDownList Sorted: True Items: AL, AK, AZ, AR, CA, CO, CT, DE, DC, FL, GA, HI, ID, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, MT, NE, NV, NH, NJ, NM, NY, NC, ND, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VT, VA, WA, WV, WI, WY Label ZIP Code     TextBox   txtCustomerZIPCode   Label Car Selected   AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft Label Tag Number:     TextBox   txtTagNumber   Label Car Condition:     ComboBox   cbxCarConditions Sorted: True Items: Needs Repair Drivable Excellent Label Make:     TextBox   txtMake   Label Model:     TextBox   txtModel   Label Year:     TextBox   txtCarYear   label Tank Level:     ComboBox   cbxTankLevels Empty 1/4 Empty 1/2 Full 3/4 Full Full Label Mileage Start:     TextBox   txtMileageStart TextAlign: Right Label Mileage End:     TextBox   txtMileageEnd TextAlign: Right Label Order Timing   AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft Label Start Date:     DateTimePicker   dtpStartDate   Label End Date:     DateTimePicker   dtpEndDate   Label Days:     TextBox 0 txtDays TextAlign: Right Label Order Status     ComboBox   cbxOrderStatus Items: Car On Road Car Returned Order Reserved Label Order Evaluation   AutoSize: False BackColor: Gray BorderStyle: FixedSingle ForeColor: White TextAlign: MiddleLeft Label Rate Applied:     TextBox 0.00 txtRateApplied TextAlign: Right Button Rental Rates btnRentalRates   Label Sub-Total:     TextBox 0.00 txtSubTotal TextAlign: Right Button Calculate btnCalculate   Label Tax Rate:     TextBox 7.75 txtTaxRate TextAlign: Right Label %     Button Save btnSave   Label Tax Amount:     TextBox 0.00 txtTaxAmount TextAlign: Right Button Print... btnPrint   Label Order Total:     TextBox 0.00 txtOrderTotal TextAlign: Right Button Print Preview... btnPrintPreview   Label Receipt #:     TextBox 0 txtReceiptNumber   Button Open btnOpen   Button New Rental Order/Reset btnNewRentalOrder   Button Close btnClose

48. Right-click the form and click View Code
49. In the Class Name combo box, select dtpStartDate
50. In the Method Name combo box, selectValueChanged and implement the event as follows:
     

    Private Sub dtpStartDate_ValueChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles dtpStartDate.ValueChanged dtpEndDate.Value = dtpStartDate.Value End Sub

51. In the Class Name combo box, select dtpEndDate
52. In the Method Name combo box, select ValueChanged and implement the event as follows:
     

    REM This event approximately evaluates the number of days as a REM difference between the end date and the starting date Private Sub dtpEndDate_ValueChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles dtpEndDate.ValueChanged Dim Days As Integer Dim DateStart As DateTime = dtpStartDate.Value Dim DateEnd As DateTime = dtpEndDate.Value REM Let's calculate the difference in days Dim tme As TimeSpan = DateEnd - DateStart Days = tme.Days REM If the customer returns the car the same day, REM we consider that the car was rented for 1 day If Days = 0 Then Days = 1 txtDays.Text = Days REM At any case, we will let the clerk specify the actual number of days End Sub

53. In the Class Name combo box, select btnRentalRates
54. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnRentalRates_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRentalRates.Click Dim RateViewer As RentalRates = New RentalRates RateViewer.Show() End Sub

55. In the Class Name combo box, select btnCalculate
56. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnCalculate_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCalculate.Click Dim Days As Integer Dim RateApplied As Double Dim SubTotal As Double Dim TaxRate As Double Dim TaxAmount As Double Dim OrderTotal As Double Try Days = CInt(txtDays.Text) Catch ex As FormatException MsgBox("Invalid Number of Days") End Try Try RateApplied = CDbl(txtRateApplied.Text) Catch ex As FormatException MsgBox("Invalid Amount for Rate Applied") End Try SubTotal = Days * RateApplied txtSubTotal.Text = FormatNumber(SubTotal) Try TaxRate = CDbl(txtTaxRate.Text) Catch ex As FormatException MsgBox("Invalid Tax Rate") End Try TaxAmount = SubTotal * TaxRate / 100 txtTaxAmount.Text = FormatNumber(TaxAmount) OrderTotal = SubTotal + TaxAmount txtOrderTotal.Text = FormatNumber(OrderTotal) End Sub

57. Return to the Order Processing form
58. From the Printing section of the Toolbox, click PrintDocument and click the form
59. In the Properties window, set its (Name) to docPrint and press Enter
60. Under the form, double-click docPrint and implement its event as follows:
     

    Private Sub docPrint_PrintPage(ByVal sender As Object, _ ByVal e As System.Drawing.Printing.PrintPageEventArgs) _ Handles docPrint.PrintPage e.Graphics.DrawLine(New Pen(Color.Black, 2), 80, 90, 750, 90) e.Graphics.DrawLine(New Pen(Color.Black, 1), 80, 93, 750, 93) Dim strDisplay As String = "Bethesda Car Rental" Dim fntString As System.Drawing.Font = _ New Font("Times New Roman", 28, _ FontStyle.Bold) e.Graphics.DrawString(strDisplay, fntString, _ Brushes.Black, 240, 100) strDisplay = "Car Rental Order" fntString = New System.Drawing.Font("Times New Roman", 22, _ FontStyle.Regular) e.Graphics.DrawString(strDisplay, fntString, _ Brushes.Black, 320, 150) e.Graphics.DrawLine(New Pen(Color.Black, 1), 80, 187, 750, 187) e.Graphics.DrawLine(New Pen(Color.Black, 2), 80, 190, 750, 190) fntString = New System.Drawing.Font("Times New Roman", 12, _ FontStyle.Bold) e.Graphics.DrawString("Receipt #: ", fntString, _ Brushes.Black, 100, 220) fntString = New System.Drawing.Font("Times New Roman", 12, _ FontStyle.Regular) e.Graphics.DrawString(txtReceiptNumber.Text, fntString, _ Brushes.Black, 260, 220) e.Graphics.DrawLine(New Pen(Color.Black, 1), 100, 240, 380, 240) fntString = New System.Drawing.Font("Times New Roman", 12, _ FontStyle.Bold) e.Graphics.DrawString("Processed By: ", fntString, _ Brushes.Black, 420, 220) fntString = New System.Drawing.Font("Times New Roman", 12, _ FontStyle.Regular) e.Graphics.DrawString(txtEmployeeName.Text, fntString, _ Brushes.Black, 550, 220) e.Graphics.DrawLine(New Pen(Color.Black, 1), 420, 240, 720, 240) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.FillRectangle(Brushes.Gray, _ New Rectangle(100, 260, 620, 20)) e.Graphics.DrawRectangle(Pens.Black, _ New Rectangle(100, 260, 620, 20)) e.Graphics.DrawString("Customer", fntString, _ Brushes.White, 100, 260) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Driver's License #: ", fntString, _ Brushes.Black, 100, 300) e.Graphics.DrawString("Name: ", fntString, _ Brushes.Black, 420, 300) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtDrvLicNumber.Text, fntString, _ Brushes.Black, 260, 300) e.Graphics.DrawString(txtCustomerName.Text, fntString, _ Brushes.Black, 540, 300) e.Graphics.DrawLine(New Pen(Color.Black, 1), 100, 320, 720, 320) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Address: ", fntString, _ Brushes.Black, 100, 330) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtCustomerAddress.Text, fntString, _ Brushes.Black, 260, 330) e.Graphics.DrawLine(New Pen(Color.Black, 1), 100, 350, 720, 350) strDisplay = txtCustomerCity.Text & " " & _ cbxCustomerStates.Text & " " & _ txtCustomerZIPCode.Text fntString = New System.Drawing.Font("Times New Roman", _ 12, FontStyle.Regular) e.Graphics.DrawString(strDisplay, fntString, _ Brushes.Black, 260, 360) e.Graphics.DrawLine(New Pen(Color.Black, 1), 260, 380, 720, 380) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.FillRectangle(Brushes.Gray, _ New Rectangle(100, 410, 620, 20)) e.Graphics.DrawRectangle(Pens.Black, _ New Rectangle(100, 410, 620, 20)) e.Graphics.DrawString("Car Information", fntString, _ Brushes.White, 100, 410) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Tag #: ", fntString, _ Brushes.Black, 100, 450) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtTagNumber.Text, fntString, _ Brushes.Black, 260, 450) e.Graphics.DrawLine(New Pen(Color.Black, 1), 100, 470, 380, 470) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Year: ", fntString, _ Brushes.Black, 420, 450) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtCarYear.Text, fntString, _ Brushes.Black, 530, 450) e.Graphics.DrawLine(New Pen(Color.Black, 1), 420, 470, 720, 470) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Make: ", fntString, _ Brushes.Black, 100, 480) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtMake.Text, fntString, _ Brushes.Black, 260, 480) e.Graphics.DrawLine(New Pen(Color.Black, 1), 100, 500, 380, 500) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Model: ", fntString, _ Brushes.Black, 420, 480) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtModel.Text, fntString, _ Brushes.Black, 530, 480) e.Graphics.DrawLine(New Pen(Color.Black, 1), 420, 500, 720, 500) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Car Condition: ", fntString, _ Brushes.Black, 100, 510) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(cbxCarConditions.Text, fntString, _ Brushes.Black, 260, 510) e.Graphics.DrawLine(New Pen(Color.Black, 1), 100, 530, 380, 530) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Tank Level: ", fntString, _ Brushes.Black, 420, 510) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(cbxTankLevels.Text, fntString, _ Brushes.Black, 530, 510) e.Graphics.DrawLine(New Pen(Color.Black, 1), 420, 530, 720, 530) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Mileage Start:", fntString, _ Brushes.Black, 100, 540) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtMileageStart.Text, fntString, _ Brushes.Black, 260, 540) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 100, 560, 380, 560) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Mileage End:", fntString, _ Brushes.Black, 420, 540) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtMileageEnd.Text, fntString, _ Brushes.Black, 530, 540) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 420, 560, 720, 560) e.Graphics.FillRectangle(Brushes.Gray, _ New Rectangle(100, 590, 620, 20)) e.Graphics.DrawRectangle(Pens.Black, _ New Rectangle(100, 590, 620, 20)) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Order Timing Information", fntString, _ Brushes.White, 100, 590) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Start Date:", fntString, _ Brushes.Black, 100, 620) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(dtpStartDate.Value.ToString("D"), _ fntString, Brushes.Black, 260, 620) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 100, 640, 720, 640) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("End Date:", fntString, _ Brushes.Black, 100, 650) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(dtpEndDate.Value.ToString("D"), _ fntString, Brushes.Black, 260, 650) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 100, 670, 520, 670) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Days:", fntString, _ Brushes.Black, 550, 650) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtDays.Text, fntString, _ Brushes.Black, 640, 650) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 550, 670, 720, 670) e.Graphics.FillRectangle(Brushes.Gray, _ New Rectangle(100, 700, 620, 20)) e.Graphics.DrawRectangle(Pens.Black, _ New Rectangle(100, 700, 620, 20)) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Order Evaluation", fntString, _ Brushes.White, 100, 700) Dim fmtString As StringFormat = New StringFormat fmtString.Alignment = StringAlignment.Far fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Rate Applied:", fntString, _ Brushes.Black, 100, 740) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtRateApplied.Text, fntString, _ Brushes.Black, 300, 740, fmtString) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 100, 760, 380, 760) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Tax Rate:", fntString, _ Brushes.Black, 420, 740) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtTaxRate.Text, fntString, _ Brushes.Black, 640, 740, fmtString) e.Graphics.DrawString("%", fntString, _ Brushes.Black, 640, 740) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 420, 760, 720, 760) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Sub-Total:", fntString, _ Brushes.Black, 100, 770) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtSubTotal.Text, fntString, _ Brushes.Black, 300, 770, fmtString) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 100, 790, 380, 790) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Tax Amount:", fntString, _ Brushes.Black, 420, 770) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtTaxAmount.Text, fntString, _ Brushes.Black, 640, 770, fmtString) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 420, 790, 720, 790) fntString = New Font("Times New Roman", 12, FontStyle.Bold) e.Graphics.DrawString("Order Total:", fntString, _ Brushes.Black, 420, 800) fntString = New Font("Times New Roman", 12, FontStyle.Regular) e.Graphics.DrawString(txtOrderTotal.Text, fntString, _ Brushes.Black, 640, 800, fmtString) e.Graphics.DrawLine(New Pen(Color.Black, 1), _ 420, 820, 720, 820) End Sub

61. Return to the Order Processing form
62. From the Printing section of the Toolbox, click PrintDialog and click the form
63. In the Properties window, change its Name to dlgPrint
64. Still in the Properties windows, set its Document property to docPrint
65. On the Order Processing form, double-click the Print button and implement its event as follows:
     

    Private Sub btnPrint_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnPrint.Click If dlgPrint.ShowDialog() = DialogResult.OK Then docPrint.Print() End If End Sub

66. Return to the Order Processing form
67. From the Printing section of the Toolbox, click PrintPreviewDialog and click the form
68. In the Properties window, change its (Name) to dlgPrintPreview
69. Still in the Properties windows, set its Document property to docPrint
70. On the Order Processing form, double-click the Print Preview button
71. Implement the event as follows:
     

    Private Sub btnPrintPreview_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnPrintPreview.Click dlgPrintPreview.ShowDialog() End Sub

72. In the Solution Explorer, right-click Form1.vb and click Rename
73. Type Central.vb and press Enter twice
74. Design the form as follows:
     

    Control Text Name Button Customers &Rental Orders btnRentalOrders Button C&ars btnCars Button &Employees btnEmployees Button &Customers btnCustomers Button C&lose btnClose

75. Double-click the Rental Orders button and implement its event as follows:
     

    Private Sub btnRentalOrders_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnRentalOrders.Click Dim dlgOrder As OrderProcessing = New OrderProcessing dlgOrder.ShowDialog() End Sub

76. In the Class Name combo box, select btnCars
77. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnCars_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCars.Click Dim dlgCars As CarEditor = New CarEditor dlgCars.ShowDialog() End Sub

78. In the Class Name combo box, select btnEmployees
79. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnEmployees_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnEmployees.Click Dim dlgEmployees As Employees = New Employees dlgEmployees.ShowDialog() End Sub

80. In the Class Name combo box, select btnCustomers
81. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnCustomers_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCustomers.Click Dim dlgCustomers As Customers = New Customers dlgCustomers.ShowDialog() End Sub

82. In the Class Name combo box, select btnClose
83. 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 Close() End Sub

84. Save all

To support dictionary-based lists, the .NET Framework provides various interfaces and classes. The interfaces allow you to create your own dictionary type of collection class. The classes allow you to directly create a dictionary-based list with an already built-in functionality. The NET Framework provides support for dictionary-based collections through two classes: Hashtable and SortedList. Both classes implement:

• The IDictionary: This makes it possible to use the DictionaryEntry class to access a key/value item
• The ICollection: This makes it possible to know the number of items in the list
• The IEnumerable: This makes it possible to use the For Each loop to enumerate the members of the list
• And the ICloneable interfaces.

The Hashtable class implements the ISerializable interface, which makes it possible for the list to be serialized. Still, the SortedList class is marked with the Serializable attribute, which makes it possible to file process its list.

The .NET Framework also provides dictionary-types through generic classes. From the System.Collections.Generic namespace, to create a dictionary type of collection, you can use either the Dictionary, the SortedDictionary, or the SortedList class. The System.Collections.Generic.Dictionary class is equivalent to the System.Collections.Hashtable class. The System.Collections.Generic.SortedList class is equivalent to the System.Collections.SortedList class. The System.Collections.Generic.SortedDictionary class is equivalent to the System.Collections.Generic.SortedList class with some differences in the way both classes deal with memory management.

If you decide to use either the System.Collections.Generic.Dictionary or the System.Collections.Generic.SortedList class, when declaring the variable, you must remember to specify the name of the class whose collection is being created.

Before using a dictionary-type of list, you can declare a variable using one of the constructors of the class. Here is an example:

Public Class Exercise

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = new Hashtable
    End Sub
End Class

In this case, the primary list would be empty.

1. In the Solution Explorer, right-click CarEditor.vb and click View Code
2. In the top section of the file, import the IO and the Binary namespace then declare a variable as follows:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class CarEditor Private ListOfCars As Dictionary(Of String, Car)

3. In the Class Name combo box, select (CarEditor Events)
4. In the Method Name combo box, select Load and implement the event as follows:
    

   Private Sub CarEditor_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load Dim vehicle As Car = New Car Dim StreamCars As FileStream Dim FormatterCars As BinaryFormatter = New BinaryFormatter REM This is the file that holds the list of items Dim Filename As String = "C:\Bethesda Car Rental\Cars.crs" lblPictureName.Text = "." If File.Exists(Filename) Then StreamCars = New FileStream(Filename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the list of cars ListOfCars = CType(FormatterCars.Deserialize(StreamCars), _ Dictionary(Of String, Car)) Finally StreamCars.Close() End Try Else ListOfCars = New Dictionary(Of String, Car) End If End Sub

5. In the Solution Explorer, right-click OrderProcessing.vb and click View Code
6. Make the following changes:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class OrderProcessing Private ReceiptNumber As Integer Private ListOfRentalOrders As SortedList(Of Integer, RentalOrder)

7. Save all

To add an item to the list, you can call the Add() method. The syntax of the System.Collections.Hashtable.Add() and the System.Collections.SortedList.Add() methods is:

Public Overridable Sub Add(key As Object, value As Object)

The syntax of the System.Collections.Generic.Dictionary.Add(), the System.Collections.Generic.SortedDictionary.Add(), and the System.Collections.Generic.SortedList.Add() method is:

Public Sub Add(key As TKey, value As TValue)

As you can see, you must provide the key and the value as the first and second arguments to the method respectively. Here are examples of calling the Add() method:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
End Sub

When calling the Add() method, you must provide a valid Key argument: it cannot be Nothing. For example, the following code would produce an error:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add(Nothing, "Hannovers")
End Sub

This would produce:

When adding the items to the list, as mentioned in our introduction, each key must be unique: you cannot have two exact keys. If you try adding a key that exists already in the list, the compiler would throw an ArgumentException exception. Based on this, the following code would not work because, on the third call, a "Patrick" key exists already:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add("Chrissie", "Hannovers")
        Students.Add("Patrick", "Herzog")
End Sub

This would produce:

This means that, when creating a dictionary type of list, you must define a scheme that would make sure that each key is unique among the other keys in the list.

Besides the Add() method, you can use the Item property to add an item to the collection. To do this, enter the Key in the parentheses of the property and assign it the desired Value. Here is an example:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add("Chrissie", "Hannovers")
        Students.Add("Patricia", "Herzog")
        Students("Michael") = "Herlander"
End Sub

1. In the Solution Explorer, right-click CarEditor.vb and click View Code
2. In the Class Name combo box, select btnSubmit
3. In the Method Name combo box, select Click and implement the Click event as follows:
    

   Private Sub btnSubmit_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnSubmit.Click Dim Vehicle As Car = New Car Dim StreamCars As FileStream Dim FormatterCars As BinaryFormatter = New BinaryFormatter Directory.CreateDirectory("C:\Bethesda Car Rental") Dim strFilename As String = "C:\Bethesda Car Rental\Cars.crs" If txtTagNumber.Text.Length = 0 Then MsgBox("You must enter the car's tag number") Exit Sub End If If txtMake.Text.Length = 0 Then MsgBox("You must specify the car's manufacturer") Exit Sub End If If txtModel.Text.Length = 0 Then MsgBox("You must enter the model of the car") Exit Sub End If If txtYear.Text.Length = 0 Then MsgBox("You must enter the year of the car") Exit Sub End If REM Create a car Vehicle.Make = txtMake.Text Vehicle.Model = txtModel.Text Vehicle.Year = CInt(txtYear.Text) Vehicle.Category = cbxCategories.Text Vehicle.HasCDPlayer = chkCDPlayer.Checked Vehicle.HasDVDPlayer = chkDVDPlayer.Checked Vehicle.IsAvailable = chkAvailable.Checked REM Call the Add method of our collection class to add the car ListOfCars.Add(txtTagNumber.Text, Vehicle) REM Save the list StreamCars = New FileStream(strFilename, _ FileMode.Create, _ FileAccess.Write, _ FileShare.Write) Try FormatterCars.Serialize(StreamCars, ListOfCars) If lblPictureName.Text.Length <> 0 Then Dim PictureFile As FileInfo = New FileInfo(lblPictureName.Text) PictureFile.CopyTo("C:\Bethesda Car Rental\" & _ txtTagNumber.Text & _ PictureFile.Extension) End If txtTagNumber.Text = "" txtMake.Text = "" txtModel.Text = "" txtYear.Text = "" cbxCategories.Text = "Economy" chkCDPlayer.Checked = False chkDVDPlayer.Checked = False chkAvailable.Checked = False lblPictureName.Text = "." pbxCar.Image = Nothing Finally StreamCars.Close() End Try End Sub

4. In the Solution Explorer, right-click Customers.vb and click View Code
5. Make the following changes:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class Customers Private ListOfCustomers As Dictionary(Of String, Customer) Private Sub ShowCustomers() End Sub Private Sub Customers_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load Dim StreamCustomers As FileStream ListOfCustomers = New Dictionary(Of String, Customer) Dim FormatterCustomers As BinaryFormatter = New BinaryFormatter REM This is the file that holds the list of parts Dim strFilename As String = "C:\Bethesda Car Rental\Customers.crc" If File.Exists(strFilename) Then StreamCustomers = New FileStream(strFilename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the list of employees from file ListOfCustomers = _ CType(FormatterCustomers.Deserialize(StreamCustomers), _ Dictionary(Of String, Customer)) Finally StreamCustomers.Close() End Try End If ShowCustomers() End Sub End Class

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

   Private Sub btnNewCustomer_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewCustomer.Click Dim bcrStream As FileStream Dim bcrBinary As BinaryFormatter = New BinaryFormatter Dim Editor As CustomerEditor = New CustomerEditor Directory.CreateDirectory("C:\Bethesda Car Rental") If Editor.ShowDialog() = DialogResult.OK Then If Editor.txtDrvLicNbr.Text = "" Then MsgBox("You must provide the driver's " & _ "license number of the customer") Exit Sub End If If Editor.txtFullName.Text = "" Then MsgBox("You must provide the employee's full name") Exit Sub End If Dim strFilename As String = "C:\Bethesda Car Rental\Customers.crc" Dim Cust As Customer = New Customer Cust.FullName = Editor.txtFullName.Text Cust.Address = Editor.txtAddress.Text Cust.City = Editor.txtCity.Text Cust.State = Editor.cbxStates.Text Cust.ZIPCode = Editor.txtZIPCode.Text ListOfCustomers.Add(Editor.txtDrvLicNbr.Text, Cust) bcrStream = New FileStream(strFilename, _ FileMode.Create, _ FileAccess.Write, _ FileShare.Write) bcrBinary.Serialize(bcrStream, ListOfCustomers) bcrStream.Close() ShowCustomers() End If End Sub

8. In the Solution Explorer, right-click Employees.vb and click View Code
9. Change the file as follows:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class Employees Private ListOfEmployees As SortedDictionary(Of String, Employee) Private Sub ShowEmployees() End Sub Private Sub Employees_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load Dim StreamEmployees As FileStream ListOfEmployees = New SortedDictionary(Of String, Employee) Dim FormatterEmployees As BinaryFormatter = New BinaryFormatter REM This is the file that holds the list of parts Dim strFilename As String = "C:\Bethesda Car Rental\Employees.cre" If File.Exists(strFilename) Then StreamEmployees = New FileStream(strFilename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the list of employees from file ListOfEmployees = _ CType(FormatterEmployees.Deserialize(StreamEmployees), _ SortedDictionary(Of String, Employee)) Finally StreamEmployees.Close() End Try End If ShowEmployees() End Sub End Class

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

    Private Sub btnNewEmployee_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewEmployee.Click Dim Editor As EmployeeEditor = New EmployeeEditor Dim bcrBinary As BinaryFormatter = New BinaryFormatter REM If this folder doesn't exist, create it Directory.CreateDirectory("C:\Bethesda Car Rental") REM Display the Employee Editor dialog box REM and find out if the user clicked OK after using it If Editor.ShowDialog() = DialogResult.OK Then REM If the user didn't provide an employee number REM don't do anything If Editor.txtEmployeeNumber.Text = "" Then MsgBox("You must provide an employee number") Exit Sub End If REM If the user didn't provide a last name, REM don't do anything If Editor.txtLastName.Text = "" Then MsgBox("You must provide the employee's last name") Exit Sub End If REM Ger a reference to the Employees file if it exists Dim strFilename As String = "C:\Bethesda Car Rental\Employees.cre" REM Get the values that the user entered in the dialog box Dim Empl As Employee = New Employee REM Create an employee from those values Empl.FirstName = Editor.txtFirstName.Text Empl.LastName = Editor.txtLastName.Text Empl.Title = Editor.txtTitle.Text Empl.HourlySalary = CDbl(Editor.txtHourlySalary.Text) REM Add the employee to the main list ListOfEmployees.Add(Editor.txtEmployeeNumber.Text, Empl) REM Save the current list of employees Dim bcrStream As FileStream = New FileStream(strFilename, _ FileMode.Create, _ FileAccess.Write, _ FileShare.Write) bcrBinary.Serialize(bcrStream, ListOfEmployees) bcrStream.Close() REM Display the list of employees ShowEmployees() End If End Sub

12. Save all

Although, or because, the key and value are distinct, to consider their combination as a single object, if you are using either the System.Collections.Hasthtable or the System.Collections.SortedList class, the .NET Framework provides the DictionaryEntry structure. To access an item, you can use the For Each loop to visit each item.

To support the For Each loop, the System.Collections.Hashtable and the System.Collections.SortedList classes implement the IEnumerable.GetEnumerator() method. In this case, the item is of type DictionaryEntry: it contains a Key and a Value in combination.

The DictionaryEntry structure contains two properties named Key and Value to identify the components of a combination. Here is an example:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                          ByVal e As System.EventArgs) _
                          Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add("Chrissie", "Hannovers")
        Students.Add("Patricia", "Herzog")
        Students("Michael") = "Herlander"

        For Each Entry As DictionaryEntry In Students
            lbxStudents.Items.Add(Entry.Key & " " & Entry.Value)
        Next
End Sub

This would produce:

If you are using a generic class, the .NET Framework provides the KeyValuePair structure that follows the same functionality as the System.Collections.DictionaryEntry structure, except that you must apply the rules of generic classes.

1. In the Solution Explorer, right-click OrderProcessing.vb and click View Code
2. In the Class Name combo box, select txtDrvLicNumber
3. In the Method Name combo box, select Leave and implement the event as follows:
    

   Private Sub txtDrvLicNumber_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtDrvLicNumber.Leave Dim Renter As Customer Dim strDrvLicNumber As String = txtDrvLicNumber.Text Dim FormatterCustomers As BinaryFormatter = New BinaryFormatter Dim ListOfCustomers As Dictionary(Of String, Customer) = _ New Dictionary(Of String, Customer) REM Make sure the user entered a driver's license number If strDrvLicNumber.Length = 0 Then MsgBox("You must enter the renter's " & _ "driver's license number") txtDrvLicNumber.Focus() Exit Sub End If REM Get a reference to the file that holds the list of customers Dim strFilename As String = "C:\Bethesda Car Rental\Customers.crc" REM Find out if that file exists If File.Exists(strFilename) Then REM If there is a file of customers, open it Dim StreamCustomers As FileStream = New FileStream(strFilename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the customers from the file and store REM them in the ListOfCustomers variable ListOfCustomers = _ CType(FormatterCustomers.Deserialize(StreamCustomers), _ Dictionary(Of String, Customer)) REM Check the list of customers to find out if there is a customer REM who has the driver's license number that the user entered If ListOfCustomers.ContainsKey(strDrvLicNumber) = True Then REM If so, get the information about that customer REM and display that information on the Order Processing form For Each Cust As KeyValuePair(Of String, Customer) In ListOfCustomers If Cust.Key = strDrvLicNumber Then Renter = Cust.Value txtCustomerName.Text = Renter.FullName txtCustomerAddress.Text = Renter.Address txtCustomerCity.Text = Renter.City cbxCustomerStates.Text = Renter.State txtCustomerZIPCode.Text = Renter.ZIPCode End If Next Else REM If there is no customer with that driver's license number REM there is nothing to display... txtCustomerName.Text = "" txtCustomerAddress.Text = "" txtCustomerCity.Text = "" cbxCustomerStates.Text = "" txtCustomerZIPCode.Text = "" REM ... and let the user know MsgBox("There is no customer with that driver's " & _ "license number in our database") Exit Sub End If Finally StreamCustomers.Close() End Try End If End Sub

4. Access the Employees.vb file and implement the ShowEmployees() procedure as follows:
    

   Private Sub ShowEmployees() If ListOfEmployees.Count = 0 Then Exit Sub End If REM Before displaying the employees, empty the list view lvwEmployees.Items.Clear() REM This variable will allow us to identify the odd and even indexes Dim Counter As Integer = 1 REM Use the KeyValuePair class to visit each key/value item For Each kvp As KeyValuePair(Of String, Employee) In ListOfEmployees Dim lviEmployee As ListViewItem = New ListViewItem(kvp.Key) Dim empl As Employee = kvp.Value lviEmployee.SubItems.Add(empl.FirstName) lviEmployee.SubItems.Add(empl.LastName) lviEmployee.SubItems.Add(empl.FullName) lviEmployee.SubItems.Add(empl.Title) lviEmployee.SubItems.Add(FormatNumber(empl.HourlySalary)) If Counter Mod 2 = 0 Then lviEmployee.BackColor = Color.FromArgb(255, 128, 0) lviEmployee.ForeColor = Color.White Else lviEmployee.BackColor = Color.FromArgb(128, 64, 64) lviEmployee.ForeColor = Color.White End If lvwEmployees.Items.Add(lviEmployee) Counter = Counter + 1 Next End Sub

5. Access the Customers.vb file and implement the ShowCustomers() method as follows:
    

   Private Sub ShowCustomers() Dim Counter As Integer If ListOfCustomers.Count = 0 Then Exit Sub End If lvwCustomers.Items.Clear() Counter = 1 For Each kvp As KeyValuePair(Of String, Customer) In ListOfCustomers Dim lviCustomer As ListViewItem = New ListViewItem(kvp.Key) Dim Cust As Customer = kvp.Value lviCustomer.SubItems.Add(Cust.FullName) lviCustomer.SubItems.Add(Cust.Address) lviCustomer.SubItems.Add(Cust.City) lviCustomer.SubItems.Add(Cust.State) lviCustomer.SubItems.Add(Cust.ZIPCode) If Counter Mod 2 = 0 Then lviCustomer.BackColor = Color.Navy lviCustomer.ForeColor = Color.White Else lviCustomer.BackColor = Color.Blue lviCustomer.ForeColor = Color.White End If lvwCustomers.Items.Add(lviCustomer) Counter = Counter + 1 Next End Sub

6. Execute the application
7. Click the Cars button and create the cars
    
8. Close the Car Editor form
9. Click the Customers button then click the New Customer button continually and create a few customers as follows:
    

   Driver's Lic. # State Full Name Address City ZIP Code M-505-862-575 MD Lynda Melman 4277 Jamison Avenue Silver Spring 20904 379-82-7397 DC John Villard 108 Hacken Rd NE Washington 20012 J-938-928-274 MD Chris Young 8522 Aulage Street Rockville 20852 497-22-0614 PA Pamela Ulmreck 12075 Famina Rd Blain 17006 922-71-8395 VA Helene Kapsco 806 Hyena Drive Alexandria 22231 C-374-830-422 MD Hermine Crasson 6255 Old Georgia Ave Silver Spring 20910 836-55-2279 NY Alan Pastore 4228 Talion Street Amherst 14228 397-59-7487 TN Phillis Buster 724 Cranston Circle Knoxville 37919 115-80-2957 FL Elmus Krazucki 808 Rasters Ave Orlando 32810 294-90-7744 VA Helena Weniack 10448 Great Pollard Hwy Arlington 22232

10. Close the Customers form

If you use the System.Collections.Hashtable or the System.Collections.Generic.Dictionary class to create your list, the items are cumulatively added to the collection every time you call the Add() method or when you use the Item property to add an item. In our introduction, we saw that the optional third rule of a dictionary type of list is that the list be sorted based on the key. To spare you the hassle of manually taking care of this, the alternative is to use the SortedList class.

Whenever a new item is added to a System.Collections.SortedList variable, a System.Collections.Generic.SortedDictionary variable, or a System.Collections.Generic.SortedList variable, the list is rearranged so the collection can be sorted in either alphabetical or chronological order based on the keys. This means that, if you want your list to be logically arranged by the keys, use one of these Sorted classes to create the collection.

1. On the Central form, click the Employees button
2. Create a few employees as follows:
    

   Employee # First Name Last Name Title Hourly Salary 62-845 Patricia Katts General Manager 42.25 92-303 Henry Larson Sales Representative 12.50 25-947 Gertrude Monay Sales Representative 14.05 73-947 Helene Sandt Intern 8.85 40-508 Melanie Karron Sales Representative 12.75 22-580 Ernest Chisen Sales Manager 22.95 20-308 Melissa Roberts Administrative Assistant 15.45

3. Notice that the list of employees is automatically sorted based on the employees numbers.
   Close the forms and return to your programming environment

After adding one or more items to the list, they are stored in two collections. The keys are stored in a collection represented by a property named Keys. The values are stored in the Values property. In the System.Collections classes, the Keys and the Values properties are of type ICollection.

To assist you with managing the keys of their collections, the System.Collections.Generic.Dictionary, the System.Collections.Generic.SortedDictionary, and the System.Collections.Generic.SortedList classes are equipped with a nested class named KeyCollection. KeyCollection is a serializable generic class that implements the ICollection interface. The only real functionalities of the nested KeyCollection class are its ability to know the current number of items in the list and the ability to enumerate the members of the collection through a For Each loop.

To assist you with the values of their lists, the System.Collections.Generic.Dictionary, the System.Collections.Generic.SortedDictionary, and the System.Collections.Generic.SortedList classes are equipped with the nested ValueCollection. The ValueCollection serializable class implements the ICollection and the IEnumerable interfaces. The functionality of the ValueCollection class is the same as its counterpart of the System.Collections namespace.

1. In the Solution Explorer, right-click OrderProcessing.vb and click View Code
2. In the Class Name combo box, select btnNewRentalOrder
3. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnNewRentalOrder_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnNewRentalOrder.Click Dim StreamRentalOrders As FileStream txtEmployeeNumber.Text = "" txtEmployeeName.Text = "" txtDrvLicNumber.Text = "" txtCustomerName.Text = "" txtCustomerAddress.Text = "" txtCustomerCity.Text = "" cbxCustomerStates.Text = "" txtCustomerZIPCode.Text = "" txtTagNumber.Text = "" cbxCarConditions.Text = "" txtMake.Text = "" txtModel.Text = "" txtCarYear.Text = "" cbxTankLevels.Text = "Empty" txtMileageStart.Text = "0" txtMileageEnd.Text = "0" dtpStartDate.Value = DateTime.Today dtpEndDate.Value = DateTime.Today txtDays.Text = "" cbxOrderStatus.Text = "" txtRateApplied.Text = "0.00" txtSubTotal.Text = "0.00" txtTaxRate.Text = "7.75" txtTaxAmount.Text = "0.00" txtOrderTotal.Text = "0.00" Dim FormatterRentalOrders As BinaryFormatter = New BinaryFormatter() Dim Filename As String = "C:\Bethesda Car Rental\RentalOrders.cro" If File.Exists(Filename) Then StreamRentalOrders = New FileStream(Filename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try ListOfRentalOrders = _ CType(FormatterRentalOrders.Deserialize(StreamRentalOrders), _ SortedList(Of Integer, RentalOrder)) ReceiptNumber = _ ListOfRentalOrders.Keys(ListOfRentalOrders.Count - 1) + 1 Finally StreamRentalOrders.Close() End Try Else ReceiptNumber = 100001 ListOfRentalOrders = New SortedList(Of Integer, RentalOrder) End If txtReceiptNumber.Text = ReceiptNumber End Sub

4. In the Class name combo box, select (OrderProcessing Events)
5. In the Method Name combo box, select Load and implement the event as follows:
    

   Private Sub OrderProcessing_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load btnNewRentalOrder_Click(sender, e) End Sub

6. Return to the Order Processing form

Locating an item in a dictionary type of list consists of looking for either a key, a value, or a combination of Key=Value. The Hashtable, the Dictionary, and the SortedList classes are equipped to handle these operations with little effort on your part. If you know the key of an item but want to find a value, you can use the Item property because it produces it. Here is an example:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add("Chrissie", "Hannovers")
        Students.Add("Patricia", "Herzog")
        Students("Michael") = "Herlander"

        For Each Entry As DictionaryEntry In Students
            lbxStudents.Items.Add(Entry.Key & " " & Entry.Value)
        Next

        Dim Value As String = CType(Students("Chrissie"), String)
        MsgBox("The value of the Chrissie key is " & Value)
End Sub

This would produce:

To find out whether a Key/Value item exists in the list, if you are using one of the classes from the System.Collections namespace, you can call the System.Collections.Hashtable.Contains() or the System.Collections.SortedList.Contains() method. Its syntax is:

Public Overridable Function Contains(key As Object) As Boolean

To look for an item, you pass its key as argument to this method. Here is an example:

Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Dim Students As Hashtable = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add("Chrissie", "Hannovers")
        Students.Add("Patricia", "Herzog")
        Students("Michael") = "Herlander"

        For Each Entry As DictionaryEntry In Students
            lbxStudents.Items.Add(Entry.Key & " " & Entry.Value)
        Next

        Dim Found As Boolean = Students.Contains("Chrissie")

        If Found = True Then
            MsgBox("The list contains an item " & _
                            "whose key is Chrissie")
        Else
            MsgBox("The list doesn't contain an " & _
                            "item whose key is Chrissie")
        End If

        Found = Students.Contains("James")

        If Found = True Then
            MsgBox("The list contains an item " & _
                        "whose key is James")
        Else
            MsgBox("The list doesn't contain an " & _
                        "item whose key is James")
        End If
End Sub

This would produce:

We have seen that the System.Collections.Hashtable.Contains() and the System.Collections.SortedList.Contains() methods allow you to find out whether a collection contains a certain specific key. An alternative is to call a method named ContainsKey.

The syntax of the System.Collections.Hashtable.ContainsKey() and the System.Collections.SortedList.ContainsKey() method is:

Public Overridable Function ContainsKey(key As Object) As Boolean

The syntax of the System.Collections.Generic.Dictionary.ContainsKey() and the System.Collections.Generic.SortedList.ContainsKey() method is:

Public Function ContainsKey(key As TKey) As Boolean

1. In the Class Name combo box, select btnSave
2. 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 If txtReceiptNumber.Text = "" Then MsgBox("The receipt number is missing") Exit Sub End If REM Don't save this rental order if we don't REM know who processed it If txtEmployeeNumber.Text = "" Then MsgBox("You must enter the employee number or the " & _ "clerk who processed this order.") Exit Sub End If REM Don't save this rental order if we don't REM know who is renting the car If txtDrvLicNumber.Text = "" Then MsgBox("You must specify the driver's license number " & _ "of the customer who is renting the car") Exit Sub End If REM Don't save the rental order if we don't REM know what car is being rented If txtTagNumber.Text = "" Then MsgBox("You must enter the tag number " & _ "of the car that is being rented") Exit Sub End If REM Create a rental order based on the information on the form Dim CurrentOrder As RentalOrder = New RentalOrder CurrentOrder.EmployeeNumber = txtEmployeeNumber.Text CurrentOrder.OrderStatus = cbxOrderStatus.Text CurrentOrder.CarTagNumber = txtTagNumber.Text CurrentOrder.CustomerDrvLicNbr = txtDrvLicNumber.Text CurrentOrder.CustomerName = txtCustomerName.Text CurrentOrder.CustomerAddress = txtCustomerAddress.Text CurrentOrder.CustomerCity = txtCustomerCity.Text CurrentOrder.CustomerState = cbxCustomerStates.Text CurrentOrder.CustomerZIPCode = txtCustomerZIPCode.Text CurrentOrder.CarCondition = cbxCarConditions.Text CurrentOrder.TankLevel = cbxTankLevels.Text Try CurrentOrder.MileageStart = CInt(txtMileageStart.Text) Catch ex As FormatException MsgBox("Invalid mileage start value") End Try Try CurrentOrder.MileageEnd = CInt(txtMileageEnd.Text) Catch ex As FormatException MsgBox("Invalid mileage End value") End Try Try CurrentOrder.DateStart = dtpStartDate.Value; Catch ex As FormatException MsgBox("Invalid start date") End Try Try CurrentOrder.DateEnd = dtpEndDate.Value; Catch ex As FormatException MsgBox("Invalid End date") End Try Try CurrentOrder.Days = CInt(txtDays.Text) Catch ex As FormatException MsgBox("Invalid number of days") End Try Try CurrentOrder.RateApplied = CDbl(txtRateApplied.Text) Catch ex As FormatException MsgBox("Invalid rate value") End Try CurrentOrder.SubTotal = CDbl(txtSubTotal.Text) Try CurrentOrder.TaxRate = CDbl(txtTaxRate.Text) Catch ex As FormatException MsgBox("Inavlid tax rate") End Try CurrentOrder.TaxAmount = CDbl(txtTaxAmount.Text) CurrentOrder.OrderTotal = CDbl(txtOrderTotal.Text) REM The rental order is ready REM Get the receipt number from its text box Try ReceiptNumber = CInt(txtReceiptNumber.Text) Catch ex As FormatException MsgBox("You must provide a receipt number") End Try REM Get the list of rental orders and REM check if there is already one with the current receipt number REM If there is already a receipt number like that... If ListOfRentalOrders.ContainsKey(ReceiptNumber) = True Then REM Simply update its value ListOfRentalOrders(ReceiptNumber) = CurrentOrder Else REM If there is no order with that receipt, REM then create a new rental order ListOfRentalOrders.Add(ReceiptNumber, CurrentOrder) End If REM The list of rental orders Dim strFilename As String = "C:\Bethesda Car Rental\RentalOrders.cro" Dim bcrStream As FileStream = New FileStream(strFilename, _ FileMode.Create, _ FileAccess.Write, _ FileShare.Write) Dim bcrBinary As BinaryFormatter = New BinaryFormatter Try bcrBinary.Serialize(bcrStream, ListOfRentalOrders) Finally bcrStream.Close() End Try End Sub

3. Save the file

To find out whether a particular value exists in the list, you can call the ContainsValue() method. The syntax of the System.Collections.Hashtable.ContainsValue() and the System.Collections.SortedList.ContainsValue() method is::

Public Overridable Function ContainsValue(value As Object) As Boolean

The syntax of the System.Collections.Generic.Dictionary.ContainsValue() and the System.Collections.Generic.SortedList.ContainsValue() method is:

Public Function ContainsValue(value As TValue) As Boolean

The ContainsKey() method allows you to only find out whether a dictionary-based collection contains a certain key. It does not identify that key and it does not give any significant information about that key, except its existence. In some operations, first you may want to find out if the collection contains a certain key. Second, if that key exists, you may want to get its corresponding value.

To assist you with both checking the existence of a key and getting its corresponding value, the generic Dictionary, SortedDictionary, and SortedList classes are equipped with a method named TryGetValue. Its syntax is:

Public Function TryGetValue(key As TKey, _
	<OutAttribute> ByRef value As TValue) As Boolean

When calling this method, the first argument must be the key to look for. If that key is found, the method returns its corresponding value as the second argument passed by reference.

1. In the Class Name combo box, select txtEmployeeNumber
2. In the Method Name combo box, select Leave and implement the event as follows:
    

   Private Sub txtEmployeeNumber_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtEmployeeNumber.Leave Dim Clerk As Employee = Nothing Dim StreamEmployees As FileStream Dim strEmployeeNumber As String = txtEmployeeNumber.Text If strEmployeeNumber.Length = 0 Then MsgBox("You must enter the employee's number") txtEmployeeNumber.Focus() Exit Sub End If Dim ListOfEmployees As SortedDictionary(Of String, Employee) = _ New SortedDictionary(Of String, Employee) Dim FormatterEmployees As BinaryFormatter = New BinaryFormatter Dim strFilename As String = "C:\Bethesda Car Rental\Employees.cre" If File.Exists(strFilename) Then StreamEmployees = New FileStream(strFilename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the list of employees ListOfEmployees = CType(FormatterEmployees.Deserialize(StreamEmployees), _ SortedDictionary(Of String, Employee)) If ListOfEmployees.TryGetValue(strEmployeeNumber, Clerk) Then txtEmployeeName.Text = Clerk.FullName Else txtEmployeeName.Text = "" MsgBox("There is no employee with that number") Exit Sub End If Finally StreamEmployees.Close() End Try End If End Sub

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

   Private Sub txtTagNumber_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtTagNumber.Leave Dim SelectedCar As Car Dim StreamCars As FileStream Dim strTagNumber As String = txtTagNumber.Text Dim ListOfCars As Dictionary(Of String, Car) = _ New Dictionary(Of String, Car) Dim FormatterCars As BinaryFormatter = New BinaryFormatter() If strTagNumber.Length = 0 Then MsgBox("You must enter the car's tag number") txtTagNumber.Focus() Exit Sub End If Dim strFilename As String = "C:\Bethesda Car Rental\Cars.crs" If File.Exists(strFilename) Then StreamCars = New FileStream(strFilename, _ FileMode.Open, _ FileAccess.Read, _ FileShare.Read) Try REM Retrieve the list of employees from file ListOfCars = CType(FormatterCars.Deserialize(StreamCars), _ Dictionary(Of String, Car)) If ListOfCars.TryGetValue(strTagNumber, SelectedCar) Then txtMake.Text = SelectedCar.Make txtModel.Text = SelectedCar.Model txtCarYear.Text = SelectedCar.Year Else txtMake.Text = "" txtModel.Text = "" txtCarYear.Text = "" MsgBox("There is no car with that tag " & _ "number in our database") Exit Sub End If Finally StreamCars.Close() End Try End If End Sub

5. In the Class Name combo box, select btnOpen
6. In the Method Name combo box, select Click and implement the event as follows:
     

   Private Sub btnOpen_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnOpen.Click Dim Order As RentalOrder = Nothing If txtReceiptNumber.Text = "" Then MsgBox("You must enter a receipt number") Exit Sub End If ReceiptNumber = CInt(txtReceiptNumber.Text) If ListOfRentalOrders.TryGetValue(ReceiptNumber, Order) Then txtEmployeeNumber.Text = Order.EmployeeNumber txtEmployeeNumber_Leave(sender, e) cbxOrderStatus.Text = Order.OrderStatus txtTagNumber.Text = Order.CarTagNumber txtTagNumber_Leave(sender, e) txtDrvLicNumber.Text = Order.CustomerDrvLicNbr txtCustomerName.Text = Order.CustomerName txtCustomerAddress.Text = Order.CustomerAddress txtCustomerCity.Text = Order.CustomerCity cbxCustomerStates.Text = Order.CustomerState txtCustomerZIPCode.Text = Order.CustomerZIPCode cbxCarConditions.Text = Order.CarCondition cbxTankLevels.Text = Order.TankLevel txtMileageStart.Text = Order.MileageStart txtMileageEnd.Text = Order.MileageEnd dtpStartDate.Value = Order.DateStart dtpEndDate.Value = Order.DateEnd txtDays.Text = Order.Days txtRateApplied.Text = FormatNumber(Order.RateApplied) txtSubTotal.Text = FormatNumber(Order.SubTotal) txtTaxRate.Text = FormatNumber(Order.TaxRate) txtTaxAmount.Text = FormatNumber(Order.TaxAmount) txtOrderTotal.Text = FormatNumber(Order.OrderTotal) Else MsgBox("There is no rental order with that receipt number") Exit Sub End If End Sub

7. In the Class Name combo box, select btnClose
8. 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 Close() End Sub

9. Execute the application
10. Create a few rental orders and print them
     
11. Close the forms and return to your programming environment
12. Execute the application again
13. Open a previously created order to simulate a customer returning a car and change some values on the form such as the return date, the mileage end, and the order status
14. Also click the Calculate button to get the final evaluation
     
15. Print the rental orders
16. Close the forms and return to your programming environment

To delete one item from the list, you can call the Remove() method. Its syntax is:

Public Overridable Sub Remove(key As Object)

Here is an example:

Public Class Exercise
    Private Students As Hashtable

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles MyBase.Load
        Students = New Hashtable

        Students.Add("Hermine", "Tolston")
        Students.Add("Patrick", "Donley")
        Students.Add("Chrissie", "Hannovers")
        Students.Add("Patricia", "Herzog")
        Students("Michael") = "Herlander"
        Students("Philemon") = "Jacobs"
        Students("Antoinette") = "Malhoun"

        For Each Entry As DictionaryEntry In Students
            lbxStudents.Items.Add(Entry.Key & " " & Entry.Value)
        Next
    End Sub

    Private Sub btnDelete_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles btnDelete.Click
        Students.Remove("Chrissie")

        lbxStudents.Items.Clear()

        For Each Entry As DictionaryEntry In Students
            lbxStudents.Items.Add(Entry.Key & " " & Entry.Value)
        Next
    End Sub
End Class

This would produce:

To delete all items from the list, you can call the Clear() method. Its syntax is:

Public Overridable Sub Clear