Mastering Visual Basic .NET

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34 Chapter 2 VISUAL BASIC PROJECTS Regardless of the language you use, you must go through the following process to develop an application: 1. Decide what the application will do and how it will interact with the user. 2. Design the application’s user interface according to the requirements of Step 1. 3. Write the actual code behind the events you want to handle. How the Loan Application Works Following the first step of the process outlined above, you decide that the user should be able to specify the amount of the loan, the interest rate, and the duration of the loan in months. You must, therefore, provide three text boxes where the user can enter these values. Another parameter affecting the monthly payment is whether payments are made at the beginning or at the end of each month, so you must also provide a way for the user to specify whether the payments will be early (first day of the month) or late (last day of the month). The most appropriate type of control for entering Yes/No or True/False type of information is the CheckBox control. This control is a toggle: If it’s checked, you can clear it by clicking it. If it’s cleared, you can check it by clicking again. The user doesn’t enter any data in this control (which means you need not anticipate user errors with this control), and it’s the simplest method for specifying values with two possible states. Figure 2.1 shows a user interface that matches our design specifications. This is the main form of the LoanCalculator project, which you will find in this chapter’s folder on the CD. Figure 2.1 LoanCalculator is a simple financial application. After the user enters all the information on the form, they can click the Show Payment button to calculate the monthly payment. The program will calculate the monthly payment and display it in the lower TextBox control. All the action takes place in the button’s Click subroutine. The function for calculating monthly payments is called Pmt() and must be called as follows: MonthlyPayment = Pmt(InterestRate, Periods, Amount, FutureValue, Due) The interest rate (argument InterestRate) is specified as a monthly rate. If the interest rate is 16.5%, the value entered by the user in the Interest Rate box should be 16.5, and the monthly rate will be 0.165 / 12. The duration of the loan (Periods) is specified in number of months, and Amount is the loan’s amount. The FutureValue of a loan is zero (it would be a positive value for an investment), and the last parameter, Due, specifies when payments are due. The value of Due can be one of the constants DueDate.BegOfPeriod and DueDate.EndOfPeriod. These two constants are built into the language, and you can use them without knowing their exact
value. In effect, this is the essence of using named constants: you type a self-descriptive name and leave it to VB to convert it to a numeric value. As you will see, .NET uses numerous constants, all of which are categorized in groups called enumerations. The constants that apply to the Due argument of the Pmt() function belong to the DueDate enumeration, which has two members, the BegOfPeriod and EndOfPeriod members. The present value of the loan is the amount of the loan with a negative sign. It’s negative because you don’t have the money now. You’re borrowing it; it’s money you owe to the bank. Future value represents the value of something at a stated time—in this case, what the loan will be worth when it’s paid off. This is what one side owes the other at the end of the specified period. So the future value of a loan is zero. Pmt() is a built-in function that uses the five values in the parentheses to calculate the monthly payment. The values passed to the function are called arguments. Arguments are the values needed by a function (or subroutine) to carry out an action or calculation. By passing different values to the function, the user can specify the parameters of any loan and calculate its monthly payment. The Pmt() function and other financial functions of Visual Basic are described in the reference “VB.NET Functions and Statements” on the CD that accompanies this book. You don’t need to know how the Pmt() function calculates the monthly payment. The Pmt() function does the calculations and returns the result. To calculate the monthly payment on a loan of $25,000 with an interest rate of 14.5%, payable over 48 months, and due the last day of the payment period (which in our case is a month), you’d call the Pmt() function as follows: Console.WriteLine(Pmt(0.145 / 12, 48, -25000, 0, DueDate.EndOfPeriod)) The value 689.448821287218 will be displayed in the Output window (you’ll see later how you can limit the digits after the decimal point to two, since this is all the accuracy you need for dollar amounts). Notice the negative sign in front of the Amount argument in the statement. If you specify a positive amount, the result will be a negative payment. The payment and the loan’s amount have different signs because they represent different cash flows. The loan’s amount is money you owe to the bank, while the payment is money you pay to the bank. The last two arguments of the Pmt() function are optional. If you omit them, Visual Basic uses their default values, which are 0 for the FutureValue argument and DueDate.BegOfPeriod for the Due argument. You can entirely omit these arguments and call the Pmt() function like this: Console.WriteLine(Pmt(0.145 / 12, 48, -25000)) BUILDING A LOAN CALCULATOR Calculating the amount of the monthly payment given the loan parameters is quite simple. What you need to know or understand are the parameters of a loan and how to pass them to the Pmt() function. You must also know how the interest rate is specified, to avoid invalid values. What you don’t need to know is how the payment is calculated—Visual Basic does it for you. This is the essence of functions: they are “black boxes” that perform complicated calculations on their arguments and return the result. You don’t have to know how they work, just how to supply the values required for the calculations. Designing the User Interface Now that you know how to calculate the monthly payment, you can design the user interface. To do so, start a new project, name it LoanCalculator, and rename its form to LoanForm. The form and the project files can be found in this chapter’s folder on the CD. 35
Page 1 and 2: Using Your Sybex Electronic Book To
Page 3 and 4: Associate Publisher: Richard Mills
Page 5 and 6: To my family
Page 7 and 8: Contents at a Glance Introduction.
Page 9 and 10: Introduction Welcome to .NET and Vi
Page 11 and 12: INTRODUCTION How About the Advanced
Page 13 and 14: INTRODUCTION browser. Web services
Page 15 and 16: Chapter 1 Getting Started with VB.N
Page 17 and 18: Figure 1.1 This is what you’ll se
Page 19 and 20: Figure 1.3 The integrated developme
Page 21 and 22: In the Properties window, also know
Page 23 and 24: THE INTEGRATED DEVELOPMENT ENVIRONM
Page 25 and 26: Figure 1.8 A simple application tha
Page 27 and 28: Listing 1.1: Processing a User-Supp
Page 29 and 30: Figure 1.10 Displaying options on a
Page 31 and 32: THE IDE COMPONENTS As you realize,
Page 33 and 34: Figure 1.13 Viewing the possible se
Page 35 and 36: THE IDE COMPONENTS Tools Menu This
Page 37 and 38: generated by the compiler, and you
Page 39 and 40: Controls expose methods, too, which
Page 41 and 42: a new application, place a Button c
Page 43 and 44: Listing 1.4: A Console Application
Page 45: Chapter 2 Visual Basic Projects The
Page 49 and 50: BUILDING A LOAN CALCULATOR 2. Place
Page 51 and 52: Show Payment button won’t have an
Page 53 and 54: ◆ The second argument is the dura
Page 55 and 56: BUILDING A LOAN CALCULATOR Exit Sub
Page 57 and 58: The Single data type can hold much
Page 59 and 60: aligned in many ways, so don’t wo
Page 61 and 62: Listing 2.4: The Clear Button Priva
Page 63 and 64: subroutine on a form on which the v
Page 65 and 66: The result variable will most likel
Page 67 and 68: clearDisplay = True End Sub Private
Page 69 and 70: VB6 programmers used the term error
Page 71 and 72: little early in the book to discuss
Page 73 and 74: TAKING THE LOANCALCULATOR TO THE WE
Page 75 and 76: Figure 2.9 Editing the Web form’s
Page 77 and 78: created and displayed. If the varia
Page 79 and 80: WORKING WITH MULTIPLE FORMS Working
Page 81 and 82: Applications designed for the Windo
Page 83 and 84: Figure 2.15 Adding a Setup and Depl
Page 85 and 86: The Manufacturer property will beco
Page 87 and 88: you’re ready to build an installe
Page 89 and 90: Verifying the Installation You alre
Page 91 and 92: Chapter 3 Visual Basic: The Languag
Page 93 and 94: Variables in VB.NET are more than j
Page 95 and 96: When you declare variables in your
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If you want to declare multiple var
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Table 3.1: Visual Basic Numeric Dat
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In a button’s Click event handler
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of the floating point, and it’s a
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and display the variable’s value:
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This listing will generate a NaN va
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Boolean operators operate on Boolea
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Char data type exposes interesting
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If the Strict option is on, you can
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Figure 3.1 Setting the Strict and E
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This is called late binding, and it
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subtle errors, and they avoid it. I
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When the Strict option is On, VB.NE
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To declare variables of this new ty
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{ use brush object to draw with } b
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numeric value, or click the Cancel
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variable without good reason. Varia
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they’re used by a couple of funct
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The name of the constant follows th
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salary, but even this data can be h
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The first element is names(0), and
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You can think of a three-dimensiona
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Note that the ReDim statement can
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VARIABLES AS OBJECTS the meantime,
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Notice that ToString is a method, n
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Formatting Dates To format dates, u
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If…Then…Else A variation of the
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The Select Case structure tests a s
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Loop Structures Loop structures all
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To execute a block of statements un
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While…End While The While…End W
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the code automatically as you edit.
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SUMMARY Summary It’s been a long
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152 Chapter 4 WRITING AND USING PRO
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Chapter 5 Working with Forms In Vis
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Clicking the icon on the left end o
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AutoScrollMinSize This property let
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Or, you can set the width and heigh
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“Building Dynamic Forms at Runtim
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Figure 5.4 A simple data-entry scre
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compares the key pressed to the F10
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Figure 5.5 The settings of the Anch
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Figure 5.8 Filling a form with two
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Figure 5.10 An elaborate form with
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There’s a better approach to impo
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As mentioned earlier, the Paint eve
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Figure 5.12 In the Properties windo
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Another technique for exposing the
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Here, PasswordForm is the name of t
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Listing 5.5: Prompting the User for
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MsgBox(MainForm.strProperty, MsgBox
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The DLG variable is declared on the
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Table 5.6: The Captions and Names o
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Programming Menu Commands Menu comm
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DESIGNING MENUS Using Access and Sh
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Table 5.7: LongMenu Command Structu
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Listing 5.11: Programming Dynamic M
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The code behind the Map Menu button
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ttn.Text = “New Button” bttn.Le
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control type. The following stateme
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Next Else For i = Me.Controls.Count
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Creating Event Handlers at Runtime
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Chapter 6 Basic Windows Controls In
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THE TEXTBOX CONTROL Basic Propertie
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THE TEXTBOX CONTROL The AcceptsTab
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Listing 6.1: Locating a String in a
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SelectedText property. To convert t
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THE TEXTBOX CONTROL Undoing Edits A
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Table 6.1: The Menu of the TextPad
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The Process and Customize Menus The
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the control to be shared. In our ca
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The code of the Find Again button i
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some custom preprocessing of the da
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With a little additional effort, yo
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Items The Items property is a colle
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Each member of the Items collection
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where item is the object to be adde
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Figure 6.7 ListDemo demonstrates mo
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The second arrow button transfers i
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If you search for “SAC”, for ex
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There’s one aspect worth mentioni
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You can also add new items at runti
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VB.NET at Work: The Colors Project
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Listing 6.17: Programming the Scrol
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The Label controls below the tick m
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Listing 6.19: SelectionChanged Even
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290 Chapter 7 MORE WINDOWS CONTROLS
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Chapter 8 Building Custom Classes C
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BUILDING THE MINIMAL CLASS you must
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The following lines will be printed
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Every time you create a new variabl
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Throw AgeException Else tAge = Valu
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Now we must do something about the
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The last two statements will print
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Note Note that the custom Equals me
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First, you must change the type of
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provide a handler for the event, th
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After this declaration, the TimerOb
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done is out of the question, so thi
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When an application initiates an op
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class’s type. If the class has al
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Note You can use the Split method o
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strNum = strNum & “ And “ & For
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openFileDialog1.ShowDialog() Consol
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Get ContactName = _contactName End
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method, so we must provide our own
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contact.EMail = txtEMail.Text conta
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So, how can we update a class that
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Original List After Elimination of
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Polymorphism This is another powerf
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If there are properties common to a
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Testing the Shape Class To test the
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Let’s start with the Triangle cla
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the month that was passed to the me
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WHO CAN INHERIT WHAT? Derived Class
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Get Property2 = “Original Propert
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Is it reasonable for a method of th
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The result of a matrix operation is
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Chapter 9 Building Custom Windows C
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ENHANCING EXISTING CONTROLS Designe
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Then save the project by selecting
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add some visual indication when a m
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Figure 9.3 The custom properties of
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Building Compound Controls A compou
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You can also specify a color value
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Building User-Drawn Controls This i
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Table 9.2: The Settings of the Effe
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The current settings of the two pro
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This subroutine calls for a few exp
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The Changed Events The UserControl
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Then, declare the following event i
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Listing 9.12: Setting Up the Two Al
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The procedures for implementing the
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The code also compares the current
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Listing 9.19: The RoundButton Contr
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ackground of each item, draw the te
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technique—for example, you can pl
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To test the enhanced ListBox contro
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Listing 9.25: Navigating to a URL w
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Chapter 10 Automating Microsoft Off
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The New keyword tells VB to create
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Objects That Represent Text The mos
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As with the Print method, the argum
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You can then apply the Range object
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of the members of the WDSelectionTy
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.Font.Size = WordApp.Selection.Font
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MsgBox(“The document contains “
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upon Word’s spell-checking routin
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Dim SpellCollection As Word.Proofre
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ListBox2.Items.Add(ListBox1.Items(w
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To access an individual worksheet,
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The Clear method resets all the cel
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Listing 10.9: Preparing a New Sprea
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Figure 10.5 This spreadsheet was cr
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to the cell, and if you read back t
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Figure 10.6 The properties of the C
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For cnt = 1 To allContacts.Items.Co
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Figure 10.8 Demonstrating how to re
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In the Messages project, you use th
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the case for users with a small num
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newNode = parentNode.Nodes.Add(subF
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Part III Basic Framework Classes In
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480 Chapter 11 STORING DATA IN COLL
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530 Chapter 12 HANDLING STRINGS, CH
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570 Chapter 13 WORKING WITH FOLDERS
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Part IV Intermediate Programming In
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620 Chapter 14 DRAWING AND PAINTING
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Chapter 15 Printing with VB.NET The
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This is same object we used in the
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dialog box was discussed in Chapter
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PrintPreviewDialog This is another
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The PrinterSettings object is a pro
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These statements will produce outpu
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e.Graphics object represents the dr
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VB.NET at Work: The PageSettings Pr
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e.Graphics.TranslateTransform(X, Y)
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X = (LMargin - strHeight) / 2 Y = T
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e.Graphics.ResetTransform() e.Graph
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each row depends on the height of t
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a line for each author. The followi
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W1 = X2 - X1 W2 = X3 - X2 W3 = page
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VB.NET at Work: The PrintText Proje
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start a new line with the last word
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on the previous page. This method i
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ectangle as possible, even if the l
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End If If PictHeight < .Height Then
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Listing 15.14: Printing a Simple Do
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SUMMARY Summary Printing is a major
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742 Chapter 16 THE TREEVIEW AND LIS
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Chapter 17 Error Handling and Debug
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Figure 17.3 Once declared, the vari
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the manager of the department calls
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Studying an Exception The exception
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exception is generated, so it’s d
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Listing 17.7: Handling an Exception
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This code is taken from a ProgressB
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The figure displays the first of th
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We’ve seen that error before—it
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SUMMARY Note There are many more ad
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812 Chapter 18 RECURSIVE PROGRAMMIN
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Chapter 19 The Multiple Document In
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MDI APPLICATIONS: THE BASICS of the
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New command. Before we can open a c
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The other four options of the Windo
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and ends with a separator. The top
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Figure 19.5 The parent menu (top le
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To access the contents of a TextBox
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Programming the New Command The New
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Listing 19.6: The Save Command Priv
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If Me.ActiveMdiChild Is Nothing The
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ttnFindNext.Enabled = True bttnRepl
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may have to maintain a list of True
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2. Rename the form to MDIImage and
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The code resizes the PictureBox con
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SUMMARY Summary In this, the last c
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Chapter 20 Databases: Architecture
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how to extract data from your datab
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Suppliers Table Each product has a
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WHAT IS A DATABASE? Exploring the P
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WHAT IS A DATABASE? is the foreign
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(basically, the driver you’ll use
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Figure 20.7 Editing the Customers t
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THE SERVER EXPLORER in the U.S., yo
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THE SERVER EXPLORER Enforce relatio
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THE SERVER EXPLORER Indexes/Keys Ta
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To make a constraint part of the da
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Alternatively, you can prefix the S
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the WHERE clause to specify how the
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names from the Customers table, you
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This statement will calculate the s
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FROM [Order Details] WHERE ProductI
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You can retrieve the same rows usin
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Limiting Groups with HAVING The HAV
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If you want to specify values for a
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operations, instead of typing compl
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If you paste this statement in the
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field in the Orders table. A new li
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dbo.Products.ProductID = dbo.[Order
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TitleAuthor, and Authors. Then chec
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This time the Query Builder will ge
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The first statement alters the proc
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Select all the text on the editor a
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it would be replaced by the second
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Chapter 21 Building Database Applic
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THE ARCHITECTURE OF ADO.NET the mod
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The first object, SqlConnection1, i
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Figure 21.2 To generate a DataSet,
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The first statement clears the curr
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to the parent table, select another
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CREATING A DATASET By default, the
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on the Data Adapter Configuration W
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Listing 21.1: Populating a DataSet
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and the Tag property to the table
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The PositionChanged() subroutine di
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and rename it to LookupCustomers. T
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DataSet. You can select a few field
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Listing 21.8: Navigating via the Li
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PROGRAMMING THE DATAADAPTER OBJECT
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Listing 21.9: Selecting Customer’
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THE COMMAND AND DATAREADER OBJECTS
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at all, and it’s certainly more e
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While SQLReader.Read txtOrders.Text
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964 Chapter 22 PROGRAMMING THE ADO.
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VB.NET on the Web Part VI In this s
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1000 Chapter 23 INTRODUCTION TO WEB
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1048 Chapter 24 ACCESSING DATA ON T
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Chapter 25 XML Web Services The las
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Building a Web Service In all previ
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The two methods are hyperlinks. Cli
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As you can see, each Web service is
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that appears (Figure 25.5), enter t
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original error message is embedded
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This is a good point to change the
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Figure 25.11 Binding a DataGrid Web
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Mastering Visual Basic .NET

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