Programming with Microsoft Visual Basic 2012 Chapter 1: An Introduction to Visual Basic 2012 Lesson A Objectives After studying Lesson A, you should be able to: • • • • • • • Start and customize Visual Studio 2012 Create a Visual Basic 2012 Windows application Manage the windows in the IDE Set the properties of an object Restore a property to its default setting Save a solution Close and open an existing solution Programming with Microsoft Visual Basic 2012 2 The Splash Screen Application Figure 1-1 Splash screen for the Red Tree Inn Programming with Microsoft Visual Basic 2012 3 The Splash Screen Application (cont.) • To start Visual Studio Professional 2012: – Click Start and point to All Programs – Select Microsoft Visual Studio 2012 – Click Visual Basic Development Settings – Click Start Visual Studio – Click WINDOW on the menu bar – Click Reset Window Layout – Click Yes at the prompt to Figure 1-2 Microsoft Visual Studio Professional 2012 startup screen restore the default layout – You can also select a different window layout using TOOLS, Settings on the menu bar Programming with Microsoft Visual Basic 2012 4 The Splash Screen Application (cont.) • To create a Visual Basic 2012 Windows application: – Click FILE on the menu bar, and then click New Project – Enter Splash Project in the Name Box – Locate a folder to store the project – Select Create Directory for Solution Programming with Microsoft Visual Basic 2012 Figure 1-3 Options dialog box 5 The Splash Screen Application (cont.) Figure 1-4 Completed New Project dialog box in Visual Studio Professional 2012 Programming with Microsoft Visual Basic 2012 6 The Splash Screen Application (cont.) Figure 1-5 Solution and Visual Basic project Programming with Microsoft Visual Basic 2012 7 The Splash Screen Application (cont.) Managing the Windows in the IDE • To open a window: – Click VIEW on the menu bar, and then click Properties Window – Or mouseover the Solution Explorer tab if the window is auto-hidden • To close a window: – Use the Close button on the window’s title bar • To minimize a window to a tab: – Click the Auto Hide (push-pin) button on the Solution Explorer window Programming with Microsoft Visual Basic 2012 8 The Splash Screen Application (cont.) Figure 1-6 Current status of the windows in the IDE Programming with Microsoft Visual Basic 2012 9 The Splash Screen Application (cont.) The Windows Form Designer Window • Used to create a graphical user interface (GUI) • Windows Form object – Create a UI by adding objects • Buttons • Text boxes – The title bar contains a default caption Figure 1-7 Windows Form Designer window • Also minimize, maximize, and close buttons Programming with Microsoft Visual Basic 2012 10 The Splash Screen Application The Solution Explorer Window • Displays a list of projects contained in the current solution and items contained in each project • Source file (cont.) Figure 1-8 Solution Explorer window – A file containing program instructions (code) • Form file – Contains code associated with a form – The first form’s code is stored in Form1.vb – The second form’s code is stored in Form2.vb Programming with Microsoft Visual Basic 2012 11 The Splash Screen Application (cont.) The Properties Window • Properties – Attributes of objects that determine appearance and behavior Figure 1-9 Properties window • Object box – Contains the name of the selected object • Properties list – Helps identify and access properties • Settings box – Shows the current values of properties Programming with Microsoft Visual Basic 2012 12 Properties of a Windows Form • System.Windows.Forms is the namespace that contains the Form class definition • A class definition is a block of code that specifies an object’s appearance and behavior • The period that separates each word in System.Windows.Forms.Form is called the dot member access operator Programming with Microsoft Visual Basic 2012 Figure 1-11 Properties window showing a partial listing of the form’s properties 13 Properties of a Windows Form (cont.) The Name Property • Windows forms have a Name property – Use it to refer to the form in the code – Naming conventions are used for clarity • Hungarian notation – frmSplash (“frm” indicates a form, and “Splash” is the form’s purpose) • Camel case – Enter ID characters in lowercase and then capitalize the first letter of each subsequent word in the name Programming with Microsoft Visual Basic 2012 14 Properties of a Windows Form (cont.) The Text Property • The Text property controls the text displayed in the form’s title bar – The default text for the Text property of Form 1 is Form1 • Change the default name to something meaningful – The Name property is used by the programmer – The Text property is read by the user when the application is running Programming with Microsoft Visual Basic 2012 15 Properties of a Windows Form (cont.) The StartPosition Property • The computer uses the form’s StartPosition property to determine the form’s initial position on the screen – Splash screens usually appear in the middle of the screen • Choose CenterScreen for the StartPosition Programming with Microsoft Visual Basic 2012 16 Properties of a Windows Form (cont.) The Font Property • A font is the general shape of a character • Font styles include regular, bold, and italic • Font sizes (8, 10, 12, etc.) are in points, with 1 point equaling 1/72 of an inch • The recommended font for applications is Segoe (pronounced SEE-go) – This is Segoe UI, Size 18 Programming with Microsoft Visual Basic 2012 17 Properties of a Windows Form (cont.) The Size Property • A form can be sized by dragging the sizing handles that appear around it • You also can size an object by selecting it and then pressing and holding down the Shift key as you press the up, down, right, or left arrow key on the keyboard • In addition, you can set the object’s Size property, which contains two numbers, measured in pixels: – The first number represents the width of the form – The second number represents the height of the form Programming with Microsoft Visual Basic 2012 18 Setting and Restoring a Property’s Value • • • • Click BackColor in the Properties list and then click the list arrow in the Settings box Click the Custom tab and then click a red square to change the background color of the form to red Now, right-click BackColor in the Properties list and then click Reset on the context menu The background color of the form returns to its default setting Programming with Microsoft Visual Basic 2012 Figure 1-12 Status of the form in the IDE 19 Saving, Closing, Opening, and Exiting a Solution Saving a Solution • An asterisk (*) appears on the designer tab whenever you make a change to the form • Save the solution by clicking FILE on the menu bar and then clicking Save All Closing the Current Solution • Click FILE on the menu bar and then click Close Solution • To exit Visual Studio 2012, click FILE on the menu bar and then click Exit Opening an Existing Solution • Click FILE on the menu bar, and then locate and open the solution from the list of filenames available Programming with Microsoft Visual Basic 2012 20 Lesson A Summary • • • • • • • Starting Visual Studio Configuring Visual Studio Creating a Visual Basic 2012 Windows application Resetting a window layout Closing and opening windows Auto-hiding a window Setting property values (name, text, location, font, size, background color) • Saving, closing, and opening solutions • Exiting Visual Studio 2012 Programming with Microsoft Visual Basic 2012 21 Lesson B Objectives After studying Lesson B, you should be able to: • • • • • • • • • Add a control to a form Set the properties of a label, picture box, and button control Select multiple controls Center controls on the form Open the Project Designer window Start and end an application Enter code in the Code Editor window Terminate an application using the Me.Close() instruction Run the project’s executable file Programming with Microsoft Visual Basic 2012 22 The Toolbox Window • Class – A pattern from which an object is created • Object – An instance with behaviors and attributes • Toolbox window (or toolbox) – Contains tools for designing a user interface – Each tool represents a class – Controls are instantiated using tools from the toolbox • Controls – GUI objects that appear on a form Programming with Microsoft Visual Basic 2012 23 The Toolbox Window (cont.) Figure 1-13 Toolbox window showing the purpose of the Label tool Programming with Microsoft Visual Basic 2012 24 The Label Tool • Used to create a label control – Displays text that cannot be edited at run time • Name property – A unique name for a control • Text property – Specifies the value that appears in a label control • Location property – Specifies the location of a control on a form – Includes an X value and a Y value Programming with Microsoft Visual Basic 2012 25 The Label Tool (cont.) Figure 1-15 Label control added to the form Programming with Microsoft Visual Basic 2012 26 The Label Tool (cont.) Setting the Text Property • Select the lblMsg control – – – – Click text in the Properties list Type A relaxing place to stay! Press Enter Verify that the AutoSize property is set to True • Select the lblName control – Click text in the Properties list – Type Red Tree Inn – Press Enter Programming with Microsoft Visual Basic 2012 27 The Label Tool (cont.) Setting the Location Property • Select the lblMsg control – – – – Click Location in the Properties list Expand the Location property by clicking the plus box Type 315, 175 Press Enter • Select the lblName control – – – – Click Location in the Properties list Expand the Location property by clicking the plus box Type 315, 130 Press Enter Programming with Microsoft Visual Basic 2012 28 Changing a Property For Multiple Controls • A control inherits the font attribute of the form – You may want to change the default values • To simultaneously modify similar controls: – Click one control and then press and hold the Ctrl key – Click other similar control(s) in the form, or click and drag to group the controls – Set the property value in the Properties list Programming with Microsoft Visual Basic 2012 29 Using the Format Menu • The Format menu provides options to manipulate form controls – Align: Aligns selected controls by left, right, top, or bottom borders – Make Same Size: Makes the width and/or height of selected controls uniform – Center in Form: Centers one or more controls • Select as the first control the one whose size or location you want to match – Called the reference control Programming with Microsoft Visual Basic 2012 30 The PictureBox Tool • Creates a picture box control – Displays an image on a form – Task box: Lists tasks associated with a picture box Figure 1-17 Open task list for a picture box • Use the task box to import an image into a project • A project’s resource file contains imported images Figure 1-18 Completed Select Resource dialog box Programming with Microsoft Visual Basic 2012 31 The PictureBox Tool (cont.) Figure 1-19 Picture boxes added to the form Programming with Microsoft Visual Basic 2012 32 The Button Tool • Used to create a button control – Used to perform an action when clicked – Examples: OK and Cancel buttons • Common means of exiting a Windows application: – Exit option on the FILE menu – Exit button Programming with Microsoft Visual Basic 2012 33 Starting and Ending an Application • Startup form – Displays when an application is first started • The Project Designer window specifies the startup form or the executable code to be run – Right-click My Project in the Solution Explorer window and then click Open – Or, click PROJECT on the menu bar and then click Properties • Application tab – Specify startup form Programming with Microsoft Visual Basic 2012 34 Starting and Ending an Application • Executable file • • • • (cont.) A file that can be run outside of the IDE Its filename ends with .exe It is automatically created when a Visual Basic application is started Two ways to start an application in the IDE: • • Click DEBUG on the menu bar and then click Start Debugging Press the F5 key Figure 1-20 Application pane in the Project Designer window Programming with Microsoft Visual Basic 2012 35 The Code Editor Window • Events – User actions such as double-clicking • Event procedure – A set of program instructions that are processed when an event occurs • Code Editor window – Provides templates for creating event procedures – To open it, right-click the form and then click View Code Programming with Microsoft Visual Basic 2012 36 The Code Editor Window (cont.) Figure 1-22 Code Editor window opened in the IDE Programming with Microsoft Visual Basic 2012 37 The Code Editor Window (cont.) • Class Name list box – Lists names of objects included in the UI • Method Name list box – Lists appropriate events for the selected object • To select a control’s event in the Code Editor window: – Select the class name first – Then select the method name • Syntax – The rules of a programming language Programming with Microsoft Visual Basic 2012 38 The Code Editor Window (cont.) • OOP – Object-oriented programming; events are clickable • Procedure header – The first line in the code template for an event procedure • Procedure footer – The last line in the code template for an event procedure • Keyword – A word that has a special meaning in a programming language – Color coded in the IDE Programming with Microsoft Visual Basic 2012 39 The Code Editor Window (cont.) • Sub procedure – A block of code that performs a specific task • Keywords in a sub procedure block: – Sub: Starts a sub procedure – Private: Restricts the use of the procedure to the form where it appears – End Sub: Indicates the end of a sub procedure • Event sub procedure names include the object name and event name – Example: btnExit.Click Programming with Microsoft Visual Basic 2012 40 The Code Editor Window (cont.) The Me.Close() Instruction • Method – A predefined procedure – Can be called (or invoked) when needed • Me.Close() method – Causes the current form to close – If it is the only form in an application, the application terminates • IntelliSense feature – Provides appropriate selections as pop-up lists – Type the first few letters of your choice – Then use the arrow keys to select an item in the list Programming with Microsoft Visual Basic 2012 41 The Code Editor Window (cont.) Figure 1-25 List displayed by the IntelliSense feature Programming with Microsoft Visual Basic 2012 42 Lesson B Summary • To add a control to a form, use a tool from the toolbox • Use the label control for text that users cannot edit • You can set the properties of multiple controls simultaneously • To start and stop an application in the IDE, use DEBUG on the menu bar • Use the Code Editor window to display an object’s event procedures • The Me.Close() method closes the current form at run time Programming with Microsoft Visual Basic 2012 43 Lesson C Objectives After studying Lesson C, you should be able to: • • • • • • Set the properties of a timer control Delete a control from the form Delete code from the Code Editor window Code a timer control’s Tick event procedure Prevent the user from sizing a form Remove and/or disable a form’s Minimize, Maximize, and Close buttons • Print an application’s code and interface Programming with Microsoft Visual Basic 2012 44 Using the Timer Tool • Splash screens typically close automatically – They do not usually contain an Exit button – The timer control removes the splash screen • Timer tool – Used to create a timer control • Timer control – Processes code at regular time intervals – Does not appear on the user interface at run time • Interval property – Specified in milliseconds • Enabled property – Allows the timer to run if set to True Programming with Microsoft Visual Basic 2012 45 Using the Timer Tool (cont.) • Tick event – Occurs each time an interval has elapsed – Condition: The timer must be running (enabled) • Add code to the Tick event procedure – Code will be run when the Tick event occurs • Component tray – A special area below the form design area in the IDE – Stores controls not visible in the user interface at run time Programming with Microsoft Visual Basic 2012 46 Using the Timer Tool (cont.) Figure 1-29 Timer control placed in the component tray Programming with Microsoft Visual Basic 2012 47 Setting the FormBorderStyle Property • FormBorderStyle property – Determines the border style of a form • Example settings: – Sizable: Allows the user to change a form’s size by dragging its borders at run time – FixedSingle: A fixed, thin border line – None: No border Programming with Microsoft Visual Basic 2012 48 The MinimizeBox, MaximizeBox, and ControlBox Properties • MinimizeBox property – Determines whether the Minimize button appears on the form’s title bar • MaximizeBox property – Determines whether the Maximize button appears on the form’s title bar • ControlBox property – Determines whether the title bar appears on the form • Splash screens typically do not contain a title bar – To remove a title bar, delete the contents of the form’s Text property Programming with Microsoft Visual Basic 2012 49 The MinimizeBox, MaximizeBox, and ControlBox Properties (cont.) Figure 1-31 Completed splash screen Programming with Microsoft Visual Basic 2012 50 Printing the Application’s Code and Interface • Printing the application’s code and user interface helps you understand and maintain the application • To print the code: – Press Prnt Scrn on the keyboard – Paste into Word or Paint and then print • To print the interface: – Click the Splash Form.vb tab to make the Code Editor window the active window – Click FILE on the menu bar, and then click Print to open the Print dialog box Programming with Microsoft Visual Basic 2012 51 Printing the Application’s Code and Interface (cont.) Figure 1-32 Print dialog box Programming with Microsoft Visual Basic 2012 52 Lesson C Summary • The timer control processes code at specified intervals • A form’s MinimizeBox and MaximizeBox properties enable or disable the Minimize and Maximize buttons on the form • A form’s ControlBox property determines whether the icon and control buttons appear in the title bar • A form’s FormBorderStyle property controls the appearance of the form’s border • Print Visual Basic code from the Code Editor window • Print the user interface from the designer window Programming with Microsoft Visual Basic 2012 53 Programming with Microsoft Visual Basic 2012 Chapter 2: Designing Applications Previewing the Play It Again Movies Application • Play It Again Movies application – Allows salespeople to enter the date and number of DVDs and Blu-rays sold – Calculates and displays the total number of discs ordered and the total sales for the order Figure 2-2 Completed sales receipt Figure 2-3 Print preview window Programming with Microsoft Visual Basic 2012 2 Lesson A Objectives After studying Lesson A, you should be able to: • Plan an object-oriented Windows application in Visual Basic 2012 • Complete a TOE (Task, Object, Event) chart • Follow the Windows standards regarding the layout and labeling of controls Programming with Microsoft Visual Basic 2012 3 Creating an Object-Oriented Application  Developing an application is like building a home  The role of the programmer is analogous to that of a builder  Bugs are problems that affect application functions Programming with Microsoft Visual Basic 2012 4 Creating an Object-Oriented Application (cont.) Figure 2-4 Processes used by a builder and a programmer Programming with Microsoft Visual Basic 2012 5 Planning an Object-Oriented Application • Actively involve the user in the planning phase – The end product should closely match the user’s needs and wants • TOE chart – Used to record tasks, objects, and events required for the application Figure 2-5 Steps for planning an OO application Programming with Microsoft Visual Basic 2012 6 Planning an Object-Oriented Application (cont.) Identifying the Application’s Tasks • What information will the application need to display on the screen and/or print on the printer? • What information is entered into the user interface? • What information will the application need to calculate to produce the desired result? • How will the user end the application? • Will previous information need to be cleared from the screen before new information is entered? Figure 2-6 Sample of the store’s current sales receipt Programming with Microsoft Visual Basic 2012 7 Planning an Object-Oriented Application (cont.) Figure 2-7 Tasks entered in a TOE chart Programming with Microsoft Visual Basic 2012 8 Planning an Object-Oriented Application (cont.) Identifying the Objects • Assign each task to an object in the user interface • Objects used here: – Label control • Displays information that the user should not change – Button control • Performs an action immediately after a Click event – Text box • Provides an area for the user to enter data Programming with Microsoft Visual Basic 2012 9 Planning an Object-Oriented Application (cont.) Figure 2-8 Tasks and objects entered in a TOE chart Programming with Microsoft Visual Basic 2012 10 Planning an Object-Oriented Application (cont.) Identifying the Events • Determine which event (if any) must occur for an object to carry out its assigned task • Text boxes and label controls – No special event is needed • btnCalc, btnClear, and btnExit buttons – Perform assigned tasks when clicked Programming with Microsoft Visual Basic 2012 11 Planning an Object-Oriented Application (cont.) Figure 2-9 Completed TOE chart ordered by task Figure 2-10 Completed TOE chart ordered by object Programming with Microsoft Visual Basic 2012 12 Planning an Object-Oriented Application (cont.) Drawing a Sketch of the User Interface • Follow Windows standards for designing the interface • In Western countries, information flows either vertically or horizontally – Vertical arrangement: • Information flows from top to bottom, with essential information located in the first column – Horizontal arrangement: • Information flows from left to right, with essential information placed in the first row Programming with Microsoft Visual Basic 2012 13 Planning an Object-Oriented Application (cont.) Figure 2-11 Vertical arrangement of the Play It Again Movies application Programming with Microsoft Visual Basic 2012 Figure 2-12 Horizontal arrangement of the Play It Again Movies application 14 Planning an Object-Oriented Application (cont.) • White space or containers may be used to group related controls • Containers – Objects used to group related controls – Examples: GroupBox, Panel, TableLayoutPanel • Label controls that display output should have meaningful names – Example: “Total Sales” identifies the lblTotalSales label • Identifying labels should end with a colon (:) – Example: “Total Sales:” Programming with Microsoft Visual Basic 2012 15 Planning an Object-Oriented Application (cont.) • Sentence capitalization – Only the first letter in the first word is capitalized – Use for identifying labels • Book title capitalization – Capitalize the first letter of each word except articles, conjunctions, and prepositions – Use for button text • Buttons should be aligned – Also same height and width • Group related controls close to each other Programming with Microsoft Visual Basic 2012 16 Planning an Object-Oriented Application (cont.) Programming with Microsoft Visual Basic 2012 17 Lesson A Summary • Steps to create an OO application: – Meet with the client – Plan the application • Identify needed tasks, objects, and events • Identify information needed as input to produce the desired result – – – – Build the user interface Code the application Test and debug the application Assemble the documentation Programming with Microsoft Visual Basic 2012 18 Lesson B Objectives After studying Lesson B, you should be able to: • Build the user interface using your TOE chart and sketch • Follow the Windows standards regarding the use of graphics, fonts, and color • Set a control’s BorderStyle, AutoSize, and TextAlign properties • Add a text box to a form • Lock the controls on the form • Assign access keys to controls • Set the TabIndex property Programming with Microsoft Visual Basic 2012 19 Building the User Interface • Use the TOE chart and sketch as guides when building the user interface – Place appropriate controls on forms – Set applicable properties of controls • Features of the UI used in this lesson’s application: – Information is arranged vertically – Controls are aligned and appropriately labeled • Try to create an interface that no one notices Programming with Microsoft Visual Basic 2012 20 Building the User Interface (cont.) Figure 2-13 Partially completed interface for the Play It Again Movies application Programming with Microsoft Visual Basic 2012 21 Building the User Interface (cont.) Including Graphics in the User Interface • Graphics – Icons or pictures added to an interface – Used to emphasize or clarify a portion of the screen, or for aesthetic purposes • The human eye is attracted to pictures before text – Include graphics sparingly – Graphics for aesthetic use should be small and positioned to avoid distracting the user Programming with Microsoft Visual Basic 2012 22 Building the User Interface (cont.) Selecting Fonts for the Interface • GUI DESIGN TIP: Selecting Font Types, Styles, and Sizes – Use only one font type—typically Segoe UI (pronounced “see-go”)—for all of the text in the interface – Use no more than two different font sizes in the interface – Avoid using italics and underlining because both font styles make text difficult to read – Limit the use of bold text to titles, headings, and key items that you want to emphasize Programming with Microsoft Visual Basic 2012 23 Building the User Interface (cont.) Adding Color to the Interface • Build the interface using black, white, and gray; only add color if you have a good reason to do so • Use white, off-white, or light gray for the background; use black for the text • Never use a dark color for the background or a light color for the text; a dark background is hard on the eyes, and lightcolored text can appear blurry • Limit the number of colors in an interface to three, not including white, black, and gray; the colors you choose should complement each other • Never use color as the only means of identifying an element in the interface Programming with Microsoft Visual Basic 2012 24 Building the User Interface (cont.) The BorderStyle, AutoSize, and TextAlign Properties • The BorderStyle property can be set to None, FixedSingle, or Fixed3D – None is used for labels – FixedSingle surrounds the control with a thin line • Used for labels that display program output – Fixed3D gives the control a three-dimensional appearance • Used for text boxes • The AutoSize property determines if a control automatically sizes to fit its current contents – Typically set to false for label controls that display program output • The TextAlign property can be set to nine different values Programming with Microsoft Visual Basic 2012 25 Building the User Interface (cont.) Adding a Text Box Control to the Form • A text box control provides an area for data entry • Use the TextBox tool to add a text box control – Make all text boxes the same size and align them using snap lines – Blue snap lines are used for vertical alignment – Pink snap lines are used for horizontal alignment Programming with Microsoft Visual Basic 2012 Figure 2-14 Snap lines shown in the interface 26 Locking the Controls on a Form • Lock controls after they are properly placed to avoid inadvertently moving them • A locked control is identified by a small lock • To lock controls: – Right-click the form (or any control on the form) – Click Lock Controls on the FORMAT menu • Follow the same procedure to unlock controls Programming with Microsoft Visual Basic 2012 27 Assigning Access Keys • Access key – Enables an object to be selected using the keyboard – Key combination: Alt key + letter or number • Each access key must be unique • Shown in the interface as an underlined letter • To assign an access key, include an ampersand (&) in the control’s caption – Example: “&Calculate Order” assigns ‘C’ to the button Programming with Microsoft Visual Basic 2012 28 Assigning Access Keys (cont.) • Reasons to assign access keys: – Allow the user to work even if the mouse does not – Allow fast typists to keep their hands on the keyboard – Allow people with disabilities that prevent them from using a mouse to be able to use an application • Follow Windows standards for assigning commonly used access keys Programming with Microsoft Visual Basic 2012 29 Controlling the Tab Order • Focus – The state in which a control is ready to accept user input or action – Pressing the Tab key or access key shifts the focus • TabIndex property – A number representing the order in which a control will receive the focus when the user presses the Tab key – A control with a TabIndex of 0 receives the focus first • Set TabIndex using the Properties window or the Tab Order option on the VIEW menu – Make a list of objects to determine the proper order Programming with Microsoft Visual Basic 2012 30 Controlling the Tab Order (cont.) Figure 2-16 TabIndex boxes showing the correct TabIndex values Figure 2-15 List of controls and TabIndex values Programming with Microsoft Visual Basic 2012 31 Lesson B Summary • Use appropriate graphics, fonts, and colors in an interface • Set the BorderStyle, AutoSize, and TextAlign properties • To lock/unlock controls on a form, use the Lock Controls option on the FORMAT menu • To assign an access key to a control, type an ampersand (&) in the Text property of the control or identifying label • To set the tab order, set the TabIndex property to a number that represents the order in which you want the control to receive the focus Programming with Microsoft Visual Basic 2012 32 Lesson C Objectives After studying Lesson C, you should be able to: • • • • • • • • • Code an application using its TOE chart Plan an object’s code using either pseudocode or a flowchart Write an assignment statement Send the focus to a control during run time Include internal documentation in the code Write arithmetic expressions Use the Val and Format functions Print an interface from code Locate and correct syntax errors Programming with Microsoft Visual Basic 2012 33 Coding the Application • Code – Instructions added to an application • Coding is done after planning and building the interface • TOE charts show which objects and events need to be coded • Play It Again Movies application code requirements: – Four buttons associated with Click events Programming with Microsoft Visual Basic 2012 34 Coding the Application (cont.) Figure 2-21 Play It Again Movies user interface from Lesson B Figure 2-22 TOE chart (ordered by object) for Play It Again Movies Programming with Microsoft Visual Basic 2012 35 Coding the Application (cont.) Using Pseudocode to Plan a Procedure • Pseudocode – Short phrases used to describe the steps a procedure must take to accomplish its goal – Travel directions are a type of pseudocode • btnCalc Click event procedure – Calculates the total number of phones ordered and the total price – Displays the results at run time Programming with Microsoft Visual Basic 2012 36 Coding the Application (cont.) Figure 2-23 Pseudocode for the Play It Again Movies application Programming with Microsoft Visual Basic 2012 37 Coding the Application (cont.) Using a Flowchart to Plan a Procedure • A flowchart shows program logic using standardized symbols – – – – Oval: Start/stop symbol Rectangle: Process symbol; represents a task Parallelogram: Input/output symbol Flowlines connect the symbols • Flowcharts depict the same logic as pseudocode Programming with Microsoft Visual Basic 2012 38 Coding the Application (cont.) Figure 2-24 Flowcharts for Play It Again Movies Programming with Microsoft Visual Basic 2012 39 Coding the btnClear Control’s Click Event Procedure • btnClear control’s task – Clear the screen for the next order • String – Zero or more characters enclosed in quotation marks ("") • Zero-length string (or empty string) – A pair of quotation marks with nothing between them ("") • Two ways to remove the control contents at run time: – Assign a zero-length string to the control’s Text property – Assign String.Empty to the control’s Text property Programming with Microsoft Visual Basic 2012 40 Coding the btnClear Control’s Click Event Procedure (cont.) Assigning a Value to a Property During Run Time • Assignment statement – An instruction assigning a value to an object at run time • Syntax: object.property = expression – object and property are the object and property names – expression contains the value to be assigned • Assignment operator (=) – Assigns the value on the right side to the object on the left side Programming with Microsoft Visual Basic 2012 Figure 2-27 First assignment statement entered in the procedure 41 Coding the btnClear Control’s Click Event Procedure (cont.) Using the Focus Method • Allows you to move the focus to a specified control during run time • Syntax: object.Focus() – object is the name of the control that receives the focus Programming with Microsoft Visual Basic 2012 42 Coding the btnClear Control’s Click Event Procedure (cont.) Internally Documenting the Program Code • Comments – Internal documentation in a program – Used by programmers to document a procedure’s purpose or explain sections of code – Help make code readable • To create a comment, place an apostrophe (’) before a statement – The computer ignores all characters after the apostrophe for the rest of the line • Comments are color-coded in the IDE Programming with Microsoft Visual Basic 2012 43 Coding the btnClear Control’s Click Event Procedure (cont.) Figure 2-28 btnClear control’s Click event procedure Programming with Microsoft Visual Basic 2012 Figure 2-29 Comments entered in the General Declarations section 44 Coding the btnPrint Control’s Click Event Procedure Figure 2-30 Syntax and examples of printing the interface from code Programming with Microsoft Visual Basic 2012 45 Coding the btnPrint Control’s Click Event Procedure (cont.) Figure 2-32 Print preview window Figure 2-33 Completed Click event procedure for the btnPrint control Programming with Microsoft Visual Basic 2012 46 Writing Arithmetic Expressions Figure 2-34 Most commonly used arithmetic operators • Order of operations: – PEMDAS (Parentheses, Exponents, Multiplication, Division, Addition, Subtraction) • Integer division operator – Returns a whole number • Modulus operator – Returns the remainder of the division Programming with Microsoft Visual Basic 2012 47 Writing Arithmetic Expressions (cont.) Figure 2-36 Expressions containing more than one operator having the same precedence Programming with Microsoft Visual Basic 2012 48 Coding the btnCalc Control’s Click Event Procedure Figure 2-37 Illustration of the total discs sold calculation Figure 2-38 Illustration of the total sales calculation Programming with Microsoft Visual Basic 2012 49 Coding the btnCalc Control’s Click Event Procedure (cont.) Figure 2-39 Interface showing the incorrect results of the calculations The Val Function • A function is a predefined procedure that performs a task and returns a value • Val temporarily converts a string to a number and returns the number • Syntax: Val(string) • You can use Val to correct calculations in the btnCalc control’s Click event procedure Programming with Microsoft Visual Basic 2012 50 Coding the btnCalc Control’s Click Event Procedure (cont.) Figure 2-40 Syntax and examples of the Val function Figure 2-41 Val function entered in the assignment statements Programming with Microsoft Visual Basic 2012 51 Coding the btnCalc Control’s Click Event Procedure (cont.) The Format Function • Improves the appearance of numbers • Syntax: Format(expression, style) – expression: Specifies the number, date, time, or string to format – style: A predefined or user-defined format style • Currency: Example of a format style that displays a number with a dollar sign and two decimal places Programming with Microsoft Visual Basic 2012 52 Coding the btnCalc Control’s Click Event Procedure (cont.) Figure 2-43 Format function’s syntax and some of the predefined format styles Programming with Microsoft Visual Basic 2012 53 Coding the btnCalc Control’s Click Event Procedure (cont.) Figure 2-44 Format function entered in the procedure Figure 2-45 Formatted total sales amount shown in the interface Programming with Microsoft Visual Basic 2012 54 Testing and Debugging the Application • Test an application using some sample data – Use both valid and invalid data • Valid data – Data that the application is expecting • Invalid data – Data that the application is not expecting • Debugging – The process of locating and correcting errors in a program – Errors can be related to either syntax or logic Programming with Microsoft Visual Basic 2012 55 Testing and Debugging the Application (cont.) • Syntax error – Occurs when a rule of a programming language is broken – Typos • Logic error – Occurs when the syntax is correct, but the outcome is not what was desired – Causes may include missing instructions, instructions out of order, or the wrong type of instruction • Run time error – Occurs when an application is running and the application stops Programming with Microsoft Visual Basic 2012 56 Testing and Debugging the Application (cont.) Figure 2-46 Suggestion for fixing the error Figure 2-47 Message dialog box Programming with Microsoft Visual Basic 2012 57 Testing and Debugging the Application (cont.) Figure 2-48 Error List window in the IDE Programming with Microsoft Visual Basic 2012 58 Assembling the Documentation • Important documentation – Planning tools – Printout of the application’s interface and code • Your planning tools include: – TOE chart – Sketch of interface – Flowcharts and/or pseudocode Programming with Microsoft Visual Basic 2012 59 Assembling the Documentation (cont.) Figure 2-49 Play It Again Movies code Programming with Microsoft Visual Basic 2012 60 Lesson C Summary • Use pseudocode or a flowchart to plan an object’s code • To assign a value to the property of an object while an application is running, use an assignment statement with the syntax object.property = expression • To create comments, begin the comment text with an apostrophe (’) • Use the integer division operator (\) to divide and return an integer result Programming with Microsoft Visual Basic 2012 61 Lesson C Summary (cont.) • Use the modulus operator to divide two numbers and return the remainder • Use the PrintForm tool to print the form • To temporarily convert a string to a number, use the Val function • Use the Format function to improve the appearance of numbers • The application should be tested with both valid and invalid data Programming with Microsoft Visual Basic 2012 62 Programming with Microsoft Visual Basic 2012 Chapter 3: Using Variables and Constants Previewing the Modified Play It Again Movies Application • Play It Again Movies application – New screen for salesclerk’s name – Sales tax added to order Figure 3-1 Name Entry dialog box Figure 3-2 Completed sales receipt Programming with Microsoft Visual Basic 2012 2 Lesson A Objectives After studying Lesson A, you should be able to: • Declare variables and named constants • Assign data to an existing variable • Convert string data to a numeric data type using the TryParse method • Convert numeric data to a different data type using the Convert class methods • Explain the scope and lifetime of variables and named constants • Explain the purpose of Option Explicit, Option Infer, and Option Strict Programming with Microsoft Visual Basic 2012 3 Using Variables to Store Information • Controls and variables temporarily store data • Variable – A temporary storage location in main memory – Specified by data type, name, scope, and lifetime • Reasons to use variables – To hold information that is not stored in a control on the form – To allow for more precise treatment of numeric data – To enable code to run more efficiently Programming with Microsoft Visual Basic 2012 4 Using Variables to Store Information (cont.) Selecting a Data Type for a Variable • Data type – Specifies the type of data a variable can store – Provides a class template for creating variables • Unicode – A universal coding scheme for characters – Assigns a unique numeric value to each character in the written languages of the world Programming with Microsoft Visual Basic 2012 5 Using Variables to Store Information (cont.) Figure 3-3 Basic data types in Visual Basic Programming with Microsoft Visual Basic 2012 6 Using Variables to Store Information (cont.) • The textbook uses: – The Integer data type for all integers – Either the Decimal or Double data type for numbers containing decimal places or numbers used in calculations – The String data type for text or numbers not used in calculations – The Boolean data type for Boolean values Programming with Microsoft Visual Basic 2012 7 Using Variables to Store Information (cont.) Selecting a Name for a Variable – Names must begin with a letter or underscore Figure 3-4 Three-character IDs and examples – Names can contain only letters, numbers, or underscores • No punctuation, special characters, or spaces are allowed – The recommended length for a name variable is 32 characters – Variable names cannot be reserved words (such as Sub or Double) Programming with Microsoft Visual Basic 2012 8 Using Variables to Store Information (cont.) • • Valid names: – intFeb_Income – decSales2014 – dblEastRegion – strName Invalid Names: – 4thQuarter • The name must begin with a letter or underscore – dblWest Region • The name cannot contain a space – strFirst.Name • The name cannot contain punctuation – decSales$East • The name cannot contain a special character Programming with Microsoft Visual Basic 2012 9 Using Variables to Store Information (cont.) Declaring a Variable • Declaration statement – Used to declare (create) a variable and reserve space in memory for it • If no initial value is given to a variable when declaring it, the computer stores a default value – – – – Numeric variables are set to 0 Boolean variables are set to False Object and String variables are set to Nothing Date variables are set to 1/1/0001 12:00:00AM Programming with Microsoft Visual Basic 2012 10 Using Variables to Store Information (cont.) Figure 3-6 Syntax and examples of a variable declaration statement Programming with Microsoft Visual Basic 2012 11 Assigning Data to an Existing Variable • Assignment statement – Assigns a value to a variable at run time – Syntax: variablename = expression – An expression may include literal constants, object properties, variables, keywords, and arithmetic operators • Literal constant – A data item whose value does not change while the application is running – Example: The string “Mary” • Literal type character – Forces a literal constant to change its data type Programming with Microsoft Visual Basic 2012 12 Assigning Data to an Existing Variable (cont.) Figure 3-7 Syntax and examples of assigning a value to a variable during run time Programming with Microsoft Visual Basic 2012 13 Assigning Data to an Existing Variable (cont.) The TryParse Method • Converts a string to a number • Is preferred over Val – Allows the programmer to specify the data type – Val only returns a Double number • Arguments – dataType: – String: – Variable: A numeric data type, such as Integer A string to be converted A variable that receives the numeric value Programming with Microsoft Visual Basic 2012 14 Assigning Data to an Existing Variable (cont.) Figure 3-9 Basic syntax and examples of the TryParse method Programming with Microsoft Visual Basic 2012 15 Assigning Data to an Existing Variable (cont.) Figure 3-10 Results of the TryParse method for the Double, Decimal and Integer data types Programming with Microsoft Visual Basic 2012 16 Assigning Data to an Existing Variable (cont.) The Convert Class • Can be used to convert a number from one type to another • Methods include ToDecimal, ToDouble, ToInt32, and ToString • TryParse is recommended for converting strings to numeric data types – Will not produce an error if the conversion fails Programming with Microsoft Visual Basic 2012 17 Assigning Data to an Existing Variable (cont.) Figure 3-11 Syntax and examples of the Convert class methods Programming with Microsoft Visual Basic 2012 18 The Scope and Lifetime of a Variable • Scope – Indicates where a variable can be used • Lifetime – How long a variable remains in memory • Scope and lifetime are determined by where a variable is declared: either the General Declarations section or the form’s Declaration section • Three types of scope: – Class: The variable can be used by all procedures in a form – Procedure: The variable can be used within a procedure – Block: The variable can be used within a specific code block Programming with Microsoft Visual Basic 2012 19 The Scope and Lifetime of a Variable (cont.) • Variables with Procedure Scope – – – – Can be used only by that procedure Declared at the beginning of the procedure Removed from memory when the procedure ends Declared using the Dim keyword • Most variables used in this course will be procedurelevel variables Figure 3-12 User Interface for the Discount Calculator application Programming with Microsoft Visual Basic 2012 20 The Scope and Lifetime of a Variable (cont.) Figure 3-13 Click event procedures using procedure-level variables Programming with Microsoft Visual Basic 2012 21 The Scope and Lifetime of a Variable (cont.) Figure 3-14 Code Editor window for the Discount Calculator application Programming with Microsoft Visual Basic 2012 22 The Scope and Lifetime of a Variable (cont.) • Variables with Class Scope – – – – Can be used by all procedures in the form Declared in the form’s Declarations section Will remain in memory until the application ends Declared using the Private keyword Figure 3-16 User Interface for the Total Scores application Programming with Microsoft Visual Basic 2012 23 The Scope and Lifetime of a Variable (cont.) Figure 3-17 Total Scores application code using a class-level variable Programming with Microsoft Visual Basic 2012 24 Static Variables • Static variable – A procedure-level variable with an extended lifetime • Remains in memory between procedure calls • Retains its value even when the procedure ends – Static keyword • Used to declare a static variable – Static variables act like class-level variables but have narrower scope • They can only be used by the procedure in which they are declared Programming with Microsoft Visual Basic 2012 25 Static Variables (cont.) Figure 3-19 Total Scores application’s code using a static variable Programming with Microsoft Visual Basic 2012 26 Named Constants • Named constant – A memory location inside the computer whose contents cannot be changed at run time • Const statement – Creates named constant – Stores value of expression in a named constant – expression: Can be a literal constant, another named constant, or an arithmetic operator – Cannot contain a variable or method Programming with Microsoft Visual Basic 2012 27 Named Constants (cont.) Figure 3-20 Syntax and examples of the Const statement Programming with Microsoft Visual Basic 2012 28 Named Constants (cont.) Figure 3-21 User interface for the Area Calculator application Figure 3-22 Calculate Area button’s Click event procedure Programming with Microsoft Visual Basic 2012 29 Option Statements Option Explicit and Option Infer • Prevent you from using undeclared variables Option Strict • Implicit type conversion – Converts the right-side value to the data type on the left side • Promotion – Data is converted to a greater precision number (e.g., Integer to Decimal) • Demotion – Data is truncated (e.g., Decimal to Integer) – Data loss can occur when demotion occurs • Infer – Ensures that every variable is declared with a data type Programming with Microsoft Visual Basic 2012 30 Option Statements (cont.) Option Strict (cont.) – Disallows implicit conversions – Type conversion rules are applied when this option is on Figure 3-24 Rules and examples of type conversions Programming with Microsoft Visual Basic 2012 31 Option Statements (cont.) Figure 3-25 Option statements entered in the General Declarations section Programming with Microsoft Visual Basic 2012 32 Lesson A Summary • • • • • • Declare a variable using {Dim | Private | Static} An assignment statement assigns a value to a variable Three levels of scope: block, procedure, class The TryParse method converts strings to numeric data Use Const to declare a named constant Avoid programming errors by using Option Explicit On, Option Infer Off, and Option Strict On Programming with Microsoft Visual Basic 2012 33 Lesson B Objectives After studying Lesson B, you should be able to: • Include procedure-level and class-level variables in an application • Concatenate strings • Get user input using the InputBox function • Include the ControlChars.NewLine constant in code • Designate the default button for a form • Format numbers using the ToString method Programming with Microsoft Visual Basic 2012 34 Modifying the Play It Again Movies Application • Modifications needed – Calculate and display the sales tax – Display salesperson’s name • • Revise the TOE chart to reflect the new tasks You must modify btnCalc button’s Click event and the form’s Load event Programming with Microsoft Visual Basic 2012 Figure 3-26 Revised TOE chart for the Play It Again Movies application 35 Modifying the Play It Again Movies Application (cont.) Figure 3-27 Modified user interface for the Play It Again Movies application Programming with Microsoft Visual Basic 2012 36 Modifying the Calculate Button’s Code • General strategy – Remove the existing code from the Click event procedure – Recode the procedure using variables in equations • Use the Option Explicit On statement – Enforces full variable declaration • Use the Option Infer Off statement – Ensures that variables are declared with data types • Use the Option Strict On statement – Suppresses implicit type conversions Programming with Microsoft Visual Basic 2012 37 Modifying the Calculate Button’s Code (cont.) Figure 3-28 A jagged blue line indicates a syntax error Figure 3-29 Lines to delete from the procedure Programming with Microsoft Visual Basic 2012 38 Modifying the Calculate Button’s Code (cont.) Figure 3-30 Revised pseudocode and flowchart for the btnCalc control’s Click event procedure Programming with Microsoft Visual Basic 2012 39 Modifying the Calculate Button’s Code (cont.) Figure 3-31 List of named constants and variables Figure 3-32 Const and Dim statements entered in the procedure Programming with Microsoft Visual Basic 2012 40 Modifying the Calculate Button’s Code (cont.) Figure 3-34 Calculated amounts shown in the interface Figure 3-33 Code entered in the btnCalc control’s Click event procedure Programming with Microsoft Visual Basic 2012 41 Concatenating Strings • Concatenate – To connect strings together • Concatenation operator – The ampersand (&) – Include a space before and after the ampersand • Numeric values used with the & operator are converted to strings Figure 3-35 Examples of string concatenation Programming with Microsoft Visual Basic 2012 42 Concatenating Strings (cont.) Figure 3-36 String concatenation included in the assignment statement Figure 3-37 Concatenated strings displayed in the lblMessage control Programming with Microsoft Visual Basic 2012 43 The InputBox Function InputBox function – Displays an input dialog box and retrieves user input • Arguments – prompt: Contains the message to display inside the dialog box – title: Controls the text that appears in the dialog box’s title bar – defaultResponse: Controls the text that appears in the input field • The returned value most often assigned to String variable • The syntax is shown in Figure 3-39 on the next slide Programming with Microsoft Visual Basic 2012 44 The InputBox Function (cont.) Figure 3-38 Example of an input dialog box Figure 3-39 Basic syntax and examples of the InputBox function Programming with Microsoft Visual Basic 2012 45 The InputBox Function (cont.) Figure 3-42 Dialog box created by the InputBox function Figure 3-40 Class-level variable declared in the form’s Declarations section Figure 3-41 frmMain Load event procedure Programming with Microsoft Visual Basic 2012 46 The ControlChars.Newline Constant ControlChars.NewLine constant – Advances the insertion point to the next line in a control – Also used to advance the insertion point in file or on the printer • To use, type ControlChars.NewLine in the appropriate location – Can be used with string concatenation • Line continuation character (_) – Used to break up a long line of code into two or more lines Programming with Microsoft Visual Basic 2012 47 The ControlChars.Newline Constant (cont.) Figure 3-43 Modified assignment statement Figure 3-45 Salesclerk’s name shown on the sales receipt Programming with Microsoft Visual Basic 2012 48 Designating a Default Button Default button – Activated by pressing the Enter key – Not required to have the focus – Only one per form • The default button should be the button used most often by the user – Except if button’s task is destructive and irreversible, such as deleting data • Set the form’s AcceptButton property to the button name Programming with Microsoft Visual Basic 2012 49 Using the ToString Method to Format Numbers • Formatting – Specifying decimal places and special characters to display • The ToString method replaces the Format function • Syntax: variablename.ToString(formatString) – variablename: The name of a numeric variable – formatString: The string specifying the format you want to use • formatString must take the form Axx, where A is the format specifier and xx is the precision specifier Programming with Microsoft Visual Basic 2012 50 Using the ToString Method to Format Numbers (Cont.) Figure 3-46 Syntax and examples of the ToString method Programming with Microsoft Visual Basic 2012 51 Using the ToString Method to Format Numbers (Cont.) Figure 3-48 Play It Again Movies application’s code at the end of Lesson B (continues…) Programming with Microsoft Visual Basic 2012 52 Using the ToString Method to Format Numbers (Cont.) Figure 3-48 Play It Again Movies application’s code at the end of Lesson B Programming with Microsoft Visual Basic 2012 53 Lesson B Summary • The concatenation operator (&) is used to link strings • The InputBox function displays an interactive dialog box • Use ControlChars.NewLine to move the insertion point to a new line • Set the default button in the form’s AcceptButton property • The ToString method formats a number for string output Programming with Microsoft Visual Basic 2012 54 Lesson C Objectives After studying Lesson C, you should be able to: • Include a static variable in code • Code the TextChanged event procedure • Create a procedure that handles more than one event Programming with Microsoft Visual Basic 2012 55 Modifying the Load and Click Event Procedures Figure 3-51 Revised TOE Chart for the Play It Again Movies application in Lesson C Programming with Microsoft Visual Basic 2012 56 Modifying the Load and Click Event Procedures (Cont.) Figure 3-52 Revised pseudocode for the Calculate button in Lesson C Programming with Microsoft Visual Basic 2012 57 Coding the TextChanged Event Procedure • TextChanged event – Occurs when the Text property value of a control changes • Can occur when: – The user enters data into the control – The code assigns data to the control’s Text property • Example: A change is made to the number of items ordered Programming with Microsoft Visual Basic 2012 58 Coding the TextChanged Event Procedure (Cont.) Associating a Procedure with Different Objects and Events • Handles clause – Appears in an event procedure’s header – Indicates the object and event associated with the procedure • You can associate an event procedure with more than one object and/or event – In the Handles section of procedure header, list each object and event separated by commas – Procedure names are entered in Pascal case • Capitalize the first letter in the name and the first letter of each subsequent word in the name Programming with Microsoft Visual Basic 2012 59 Coding the TextChanged Event Procedure (cont.) Figure 3-53 TextChanged event procedure associated with the txtDvds control Figure 3-54 Completed ClearLabels procedure Programming with Microsoft Visual Basic 2012 60 Lesson C Summary • The TextChanged event procedure responds to a change in the value of a control’s Text Property • The Handles clause determines which objects and events are associated with the event procedure • To create a procedure for more than one object or event, list each object and event after the Handles keyword Programming with Microsoft Visual Basic 2012 61
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