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Chapter 2: Designing Applications

Chapter 2: Designing Applications. Programming with Microsoft Visual Basic .NET, Second Edition. Planning an Object-Oriented (OO) Application in Visual Basic .NET Lesson A Objectives. Plan an OO application in Visual Basic .NET Complete a TOE (Task, Object, Event) chart

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Chapter 2: Designing Applications

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  1. Chapter 2: Designing Applications Programming with Microsoft Visual Basic .NET, Second Edition

  2. Planning an Object-Oriented (OO) Application in Visual Basic .NET Lesson A Objectives • Plan an OO application in Visual Basic .NET • Complete a TOE (Task, Object, Event) chart • Follow the Windows standards regarding the layout and labeling of controls Programming with Microsoft Visual Basic .NET, Second Edition

  3. Solving the Problem Using a Procedure-Oriented Approach • Emphasis of a program is on how to accomplish a task • A flowchart uses standardized symbols to show the steps needed to solve a problem • Pseudocode uses English phrases to describe the required steps • User has little, if any, control Programming with Microsoft Visual Basic .NET, Second Edition

  4. Solving the Problem Using an Object-Oriented (OO) Approach • Emphasis of a program is on the objects included in the interface and the events that occur on those objects • You will use a TOE (Task, Object, Event) chart to assist you in planning your object-oriented programs • User has a lot of control Programming with Microsoft Visual Basic .NET, Second Edition

  5. Solving the Problem Using an Object-Oriented (OO) Approach (continued) Sample TOE chart Programming with Microsoft Visual Basic .NET, Second Edition

  6. Creating an OO Application Figure 2-6: Processes used by a builder and a programmer Programming with Microsoft Visual Basic .NET, Second Edition

  7. Planning an OO Application • Actively involve the user in the planning phase • Planning an OO application requires the following steps: • Identify the tasks the application needs to perform • Identify the objects to which you will assign those tasks • Identify the events required to trigger an object into performing its assigned tasks • Draw a sketch of the user interface Programming with Microsoft Visual Basic .NET, Second Edition

  8. Identifying the Application’s Tasks • What information, if any, will the application need to display on the screen and/or print on the printer? • What information, if any, will the user need to enter into the user interface to display and/or print the desired information? • What information, if any, will the application need to calculate to display and/or print the desired information? Programming with Microsoft Visual Basic .NET, Second Edition

  9. Identifying the Application’s Tasks (continued) • How will the user end the application? • Will previous information need to be cleared from the screen before new information is entered? Programming with Microsoft Visual Basic .NET, Second Edition

  10. Identifying the Objects • After completing the Task column of the TOE chart, you then assign each task to an object in the user interface • You use a label control to display information that you do not want the user to change • You use a button control to perform an action immediately after it is clicked by the user • You use a text box to give the user an area in which to enter data Programming with Microsoft Visual Basic .NET, Second Edition

  11. Identifying the Events • Text boxes and Label controls display their contents automatically - no special event is needed • The remaining objects are the three buttons: uiCalcButton, uiClearButton, and uiExitButton • Have the buttons perform their assigned tasks when they are clicked by the user Programming with Microsoft Visual Basic .NET, Second Edition

  12. Drawing a Sketch of the User Interface • In Western countries, organize the user interface so that the information flows either vertically or horizontally • In a vertical arrangement • The information flows from top to bottom • The essential information is located in the first column of the screen • Secondary information is placed in subsequent columns Programming with Microsoft Visual Basic .NET, Second Edition

  13. Drawing a Sketch of the User Interface (continued) • In a horizontal arrangement • The information flows from left to right • The essential information is placed in the first row of the screen • Secondary information placed in subsequent rows • You can use white space, a GroupBox control, or a Panel control to group related controls together Programming with Microsoft Visual Basic .NET, Second Edition

  14. Drawing a Sketch of the User Interface (continued) • If buttons appear in the interface, they should be positioned either in a row along the bottom of the screen, or stacked in either the upper-right or lower-right corner • Each text box and button control should be labeled so the user knows the control’s purpose • The Windows standard is to use sentence capitalization for identifying labels Programming with Microsoft Visual Basic .NET, Second Edition

  15. Building the User InterfaceLesson B Objectives • Build the user interface using TOE chart and sketch • Follow the Windows standards regarding the use of graphics, color, and fonts • Set the BorderStyle property • Add a text box to a form Programming with Microsoft Visual Basic .NET, Second Edition

  16. Building the User InterfaceLesson B Objectives (continued) • Lock the controls on the form • Assign access keys to controls • Use the TabIndex property Programming with Microsoft Visual Basic .NET, Second Edition

  17. Preparing to Create the User Interface • Maintain a consistent margin of two or three dots from the edge of the window • Position related controls on succeeding dots • Controls that are not part of any logical grouping may be positioned from two to four dots away from other controls • Try to create an interface that no one notices Programming with Microsoft Visual Basic .NET, Second Edition

  18. Including Graphics in the User Interface • The human eye is attracted to pictures before text; include a graphic only if it is necessary • If the graphic is for aesthetics only, use a small graphic and place it so as not to distract the user Programming with Microsoft Visual Basic .NET, Second Edition

  19. Including Different Fonts in the User Interface • Use 8, 10, or 12 point fonts for the elements in the user interface • Use only one or two font sizes • Use only one font type for all of the text • Avoid italic and underlining • Limit the use of bold text to titles, headings, and key items Programming with Microsoft Visual Basic .NET, Second Edition

  20. Including Color in the User Interface • Use either white, off-white, light gray, pale blue, or pale yellow for an application’s background, and use black for the text • Always use dark text on a light background • Never use a dark color for the background or a light color for the text • Limit the number of colors (other than white, black, and gray) to three Programming with Microsoft Visual Basic .NET, Second Edition

  21. The BorderStyle Property • BorderStyle property determines the style of a control’s border • Set the BorderStyle property of text boxes to Fixed3D • Set the BorderStyle property of labels that identify other controls to None • Set the BorderStyle property of labels that display program output to FixedSingle Programming with Microsoft Visual Basic .NET, Second Edition

  22. Adding a Text Box Control to the Form • A text box control provides an area in the form where the user can enter data • Add the missing text box control to the form and then set its properties Programming with Microsoft Visual Basic .NET, Second Edition

  23. Locking the Controls on a Form • Once you have placed all of the controls in the desired locations, lock them so you do not inadvertently move them • Once locked, you cannot move them until you unlock them; you can, however, delete them Programming with Microsoft Visual Basic .NET, Second Edition

  24. Assigning Access Keys • An access key allows the user to select an object by using the Alt key in combination with a letter or number • Each access key must be unique • You can assign an access key to any control that has a Caption property Programming with Microsoft Visual Basic .NET, Second Edition

  25. Assigning Access Keys (continued) • Place an & to the left of the desired letter in the Text property • To give keyboard access to a text box, assign an access key to its identifying label, then set the label’s TabIndex value to one less than the text box’s TabIndex value Programming with Microsoft Visual Basic .NET, Second Edition

  26. Setting the TabIndex Property • The TabIndex property determines the order in which a control receives the focus when the user presses either the Tab key or an access key while the application is running • When a control has the focus, it can accept user input • To determine the appropriate TabIndex settings for an application, make a list of the controls that can accept user input Programming with Microsoft Visual Basic .NET, Second Edition

  27. Setting the TabIndex Property (continued) • The list should reflect the order in which the user will want to access the controls • After listing the controls, assign each control in the list a TabIndex value, beginning with the number 0 • You can use the Properties list to set the TabIndex property for each control; or, you can use the Tab Order option on the View menu Programming with Microsoft Visual Basic .NET, Second Edition

  28. Coding, Testing, Debugging, and Documenting the ApplicationLesson C Objectives • Use the TOE chart to code the application • Use pseudocode to plan an object’s code • Write an assignment statement • Use the Focus method Programming with Microsoft Visual Basic .NET, Second Edition

  29. Coding, Testing, Debugging, and Documenting the ApplicationLesson C Objectives (continued) • Include internal documentation in the code • Write arithmetic expressions • Use the Val and Format functions Programming with Microsoft Visual Basic .NET, Second Edition

  30. Coding the Application • Instructions are called code • The process of writing the instructions is called coding • Use pseudocode to help you plan the code • Internally document the code by placing an apostrophe before the comment in the Code window Programming with Microsoft Visual Basic .NET, Second Edition

  31. Coding the Clear Screen Button • According to the TOE chart, the Clear Screen button is assigned the task of clearing the screen for the next order • A zero-length string (empty string), is a pair of quote marks with nothing between them: “” • Assigning a zero-length string to the Text property of a control removes its contents Programming with Microsoft Visual Basic .NET, Second Edition

  32. Coding the Clear Screen Button (continued) • The pseudocode shown in Figure 2-25 represents the steps the Clear Screen button needs to prepare the screen for the next order • The programmer uses the pseudocode as a guide when coding the application • You use an assignment statement, which is simply a Visual Basic .NET instruction, to set the value of a property while an application is running Programming with Microsoft Visual Basic .NET, Second Edition

  33. Coding the Clear Screen Button (continued) Figure 2-25: Steps for the Clear Screen button Programming with Microsoft Visual Basic .NET, Second Edition

  34. Assigning a Value to a Property During Run Time • Use the syntax [Me.]object.property=expression to set the value of an object’s property while an application is running • In an assignment statement, the equal sign (=) is called the assignment operator • The value of the expression on the right side of an = is assigned to the object and property that appears on the left side Programming with Microsoft Visual Basic .NET, Second Edition

  35. Using the Focus Method • A method is a predefined procedure • The Focus method allows you to move the focus to a specified control • The syntax of the Focus method: [Me.]object.Focus() Programming with Microsoft Visual Basic .NET, Second Edition

  36. Internally Documenting the Program Code • Visual Basic .NET provides an easy way to document a program internally • Place an apostrophe (‘) before the statement you want treated as a comment • Visual Basic .NET ignores everything that appears after the apostrophe on that line Programming with Microsoft Visual Basic .NET, Second Edition

  37. Writing Arithmetic Expressions • The precedence numbers indicate the order in which Visual Basic .NET performs the operation in an expression • Operations with a lower precedence number are performed before operations with a higher precedence number Programming with Microsoft Visual Basic .NET, Second Edition

  38. Writing Arithmetic Expressions (continued) • Use parentheses to override the precedence • Use the integer division operator (\) to divide two integers and return the result as an integer • The modulus operator returns the remainder after integer division Programming with Microsoft Visual Basic .NET, Second Edition

  39. Writing Arithmetic Expressions (continued) Figure 2-34: Arithmetic operators and their order of precedence Programming with Microsoft Visual Basic .NET, Second Edition

  40. Coding the Calculate Order Button • The Calculate Order button is responsible for: • Calculating both the total number of skateboards ordered and the total price of the order • Displaying the calculated amounts in the uiTotalBoardsLabel and uiTotalPriceLabel controls • The instructions to accomplish the Calculate Order button’s tasks should be placed in the button’s Click event procedure Programming with Microsoft Visual Basic .NET, Second Edition

  41. Coding the Calculate Order Button (continued) Figure 2-35: Pseudocode for the Calculate Order button Programming with Microsoft Visual Basic .NET, Second Edition

  42. The Val Function • Like a method, a function is a predefined procedure that performs a specific task • The Val function temporarily converts a string to a number, and then returns the number • Syntax of the Val function is Val(string), where string is the string you want treated as a number Programming with Microsoft Visual Basic .NET, Second Edition

  43. Using the Format Function • Syntax: Format(expression, style) • Expression specifies the number, date, time, or string whose appearance you want to format • Style is either the name of a predefined Visual Basic .NET format style or a string containing symbols that indicate how you want the expression displayed Programming with Microsoft Visual Basic .NET, Second Edition

  44. Testing and Debugging the Application • Test an application by starting it and entering some sample data • Use both valid (expected) and invalid (unexpected) test data Programming with Microsoft Visual Basic .NET, Second Edition

  45. Testing and Debugging the Application (continued) • Debugging: locating errors in the program • Errors can be either syntax or logic • Most syntax errors are simply typing errors • Logic errors occur when you enter an instruction that does not give the expected results Programming with Microsoft Visual Basic .NET, Second Edition

  46. Assembling the Documentation • Assembling the documentation refers to putting in a safe place your planning tools and a printout of the application’s interface and code • Your planning tools include: • The TOE chart • Sketch of the interface • Flowcharts and/or pseudocode Programming with Microsoft Visual Basic .NET, Second Edition

  47. Summary • Steps to create an OO application: • Meet with the client • Plan the application • Build the user interface • Code the application • Test and debug the application • Assemble the documentation Programming with Microsoft Visual Basic .NET, Second Edition

  48. Summary (continued) • To control the border around a label control, set the label control’s BorderStyle property • To assign an access key to a control, type an ampersand (&) in the Text property of the control’s caption or identifying label • To set the tab order, set each control’s TabIndex property to a number that represents the order in which you want the control to receive the focus Programming with Microsoft Visual Basic .NET, Second Edition

  49. Summary (continued) • To assign a value to the property of an object while an application is running, use an assignment statement that follows the syntax:[Me.]object.property = expression • To document Visual Basic code with comments, begin the comment with an apostrophe (’) • To temporarily convert a string to a number, use the Val function Programming with Microsoft Visual Basic .NET, Second Edition

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