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Chapter 2: Designing Applications

Chapter 2: Designing Applications. Programming with Microsoft Visual Basic 2005, Third Edition. Planning an Object-Oriented (OO) Application in Visual Basic 2005 Lesson A Objectives. Plan an OO application in Visual Basic 2005 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 2005, Third Edition

  2. Planning an Object-Oriented (OO) Application in Visual Basic 2005 Lesson A Objectives • Plan an OO application in Visual Basic 2005 • Complete a TOE (Task, Object, Event) chart • Follow the Windows standards regarding the layout and labeling of controls Programming with Microsoft Visual Basic 2005, Third Edition

  3. Solving the Problem Using a Procedure-Oriented Approach • Emphasis is on how to accomplish a task • Flowchart • Document representing program logic • Standardized symbols show problem-solving steps • Pseudocode • English phrases describing the required steps • User has little, if any, control over the program Programming with Microsoft Visual Basic 2005, Third Edition

  4. Solving the Problem Using an Object-Oriented (OO) Approach • Object-oriented programs • Include objects that respond to events; e.g., clicks • Examples of objects appearing on an interface • Buttons, picture boxes, list boxes, text boxes, labels • TOE (Task, Object, Event)chart • Used to plan your object-oriented programs • User has more control over program execution Programming with Microsoft Visual Basic 2005, Third Edition

  5. Solving the Problem Using an Object-Oriented (OO) Approach (continued) Figure 2-4: Order screen created by the OO application Programming with Microsoft Visual Basic 2005, Third Edition

  6. Creating an OO Application • Developing an application is like building a home • Role of programmer analogous to that of builder • Bugs: problems that affect application functions Programming with Microsoft Visual Basic 2005, Third Edition

  7. Creating an OO Application (continued) Figure 2-6: Processes used by a builder and a programmer Programming with Microsoft Visual Basic 2005, Third Edition

  8. Planning an OO Application • Actively involve the user in the planning phase • Steps involved in planning an OO application • Identify the tasks the application needs to perform • Identify objects to which tasks will be assigned • Identify events causing an object to perform tasks • Draw a sketch of the user interface • Use a TOE chart to record tasks, objects, events Programming with Microsoft Visual Basic 2005, Third Edition

  9. 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 2005, Third Edition

  10. 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 2005, Third Edition

  11. Identifying the Objects • Each task is assigned to an object in the interface • Objects used: label control, button control, text box • Label control • Displays information that user should not change • Button control • Performs an action immediately after a click event • Text box: provides an area for user to enter data Programming with Microsoft Visual Basic 2005, Third Edition

  12. Identifying the Events • Seven text boxes get and display order information • No special event is needed • Two label controls display quantity and total price • No special event is needed • xCalcButton, xClearButton, and xExitButton • Have buttons perform assigned tasks when clicked Programming with Microsoft Visual Basic 2005, Third Edition

  13. Identifying the Events (continued) Figure 2-11: Completed TOE chart ordered by object Programming with Microsoft Visual Basic 2005, Third Edition

  14. Drawing a Sketch of the User Interface • Organizing the user interface in Western countries • Information flows either vertically or horizontally • Vertical arrangement • Information flows from top to bottom • Essential information is located in the first column • Horizontal arrangement • The information flows from left to right • Essential information is placed in the first row Programming with Microsoft Visual Basic 2005, Third Edition

  15. Drawing a Sketch of the User Interface (continued) Figure 2-12: Vertical arrangement of the Skate-Away Sales interface Programming with Microsoft Visual Basic 2005, Third Edition

  16. Drawing a Sketch of the User Interface (continued) Figure 2-13: Horizontal arrangement of the Skate-Away Sales interface Programming with Microsoft Visual Basic 2005, Third Edition

  17. Drawing a Sketch of the User Interface (continued) • White space may be used to group related controls • Containers: objects used to group related controls • Examples: group box, panel, table layout panel • Interface elements should have meaningful labels • Example: “Name” identifies xNameTextBox • Follow other stylistic conventions in layout • Example: size buttons should be proportional Programming with Microsoft Visual Basic 2005, Third Edition

  18. Summary – Lesson A • 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 2005, Third Edition

  19. Building the User InterfaceLesson B Objectives • Build the user interface using your TOE chart and sketch • Follow the Windows standards regarding the use of graphics, color, and fonts • Set a control’s BorderStyle property • Add a text box to a form Programming with Microsoft Visual Basic 2005, Third Edition

  20. 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 2005, Third Edition

  21. Preparing to Create the User Interface • TOE chart and sketch guide two major tasks • Placing the appropriate controls on forms • Setting applicable properties of the controls • Some features of the user interface • Information is arranged vertically • Controls are aligned and appropriately labeled • Try to create an interface that no one notices Programming with Microsoft Visual Basic 2005, Third Edition

  22. Preparing to Create the User Interface (continued) Figure 2-14: Partially completed interface for the Skate-Away Sales application Programming with Microsoft Visual Basic 2005, Third Edition

  23. Including Graphics in the User Interface • Graphics: icons or pictures added to an interface • The human eye is attracted to pictures before text • Include a graphic only if it is necessary • Graphics for aesthetic use should be small • Avoid distracting the user Programming with Microsoft Visual Basic 2005, Third Edition

  24. Including Different Fonts in the User Interface • Font property: controls font type, style, and size • Recommendations for setting fonts • Use sans serif fonts (without strokes); e.g. Tahoma • Use 8 - 12 point fonts for user interface elements • Use only one or two font sizes and one font type • Avoid italics and underlining, limit bold text • Objects added to a form inherit form’s font setting Programming with Microsoft Visual Basic 2005, Third Edition

  25. Including Color in the User Interface • The eye is drawn to color before black and white • Guidelines for adding colors • Use dark text against a light background • Add up to three, not including black, white, gray • Colors added should be complementary • Avoid using a dark color for the background • Use color to help identify interface elements Programming with Microsoft Visual Basic 2005, Third Edition

  26. The BorderStyle Property • BorderStyle property • Determines the style of a control’s border • Three ways to set the BorderStyle property • None: ensures control will not have a border • FixedSingle: surrounds control with a thin line • Fixed3D: gives control a 3-D appearance • Example: text box BorderStyle often set to Fixed3D Programming with Microsoft Visual Basic 2005, Third Edition

  27. Adding a Text Box Control to the Form • Text box control • Provides an area in the form for data entry • Use the TextBox tool to add a text box control Programming with Microsoft Visual Basic 2005, Third Edition

  28. Adding a Text Box Control to the Form (continued) Figure 2-16: Form showing the correct location of the City text box Programming with Microsoft Visual Basic 2005, Third Edition

  29. Locking the Controls on a Form • Lock controls after they are properly placed • Purpose: avoid inadvertently moving controls • A locked control is identified by a small-lock • One way to lock controls • Click the form (or any control on the form) • Click Format on the menu bar • Click Lock Controls • Follow the same procedure to unlock the controls Programming with Microsoft Visual Basic 2005, Third Edition

  30. Assigning Access Keys • Access key • Enables object to be selected using keyboard • Key combination: Alt key + letter or number • Each access key must be unique • Assigning an access key • Include an ampersand (&) in the control’s caption • Example: &CalculateOrder assigns ‘C’ to button Programming with Microsoft Visual Basic 2005, Third Edition

  31. Setting the TabIndex Property • Focus: control state allowing a user to enter input • Pressing Tab or access key shifts focus • TabIndex property • Determines when a control receive will receive focus • Example: label with TabIndex of 0 receives focus first • Revise TabIndex using Properties or Tab Order • Make a list of objects to determine proper ordering Programming with Microsoft Visual Basic 2005, Third Edition

  32. Summary – Lesson B • 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 2005, Third Edition

  33. Coding, Testing, Debugging, and Documenting the ApplicationLesson C Objectives • Code an application using its TOE chart • Plan an object’s code using pseudocode or a flowchart • Write an assignment statement • Send the focus to a control while an application is running Programming with Microsoft Visual Basic 2005, Third Edition

  34. 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 2005, Third Edition

  35. Coding the Application • Code: instructions added to an application • Coding follows planning and building of interface • TOE charts show which objects and events to code • Skate-Away Sales application code requirements • Three buttons associated with Click events • Use pseudocode or flowchart to design procedure Programming with Microsoft Visual Basic 2005, Third Edition

  36. Using Pseudocode to Plan a Procedure • Pseudocode: instructions in English syntax • Short phrases describe the steps of a procedure • Travel directions are a type of pseudocode • xExitButton Click Event Procedure (pseudocode) • End the application Programming with Microsoft Visual Basic 2005, Third Edition

  37. Using a Flowchart to Plan a Procedure • Flowchart • Uses standardized symbols to show program logic • Pseudocode can be used within symbols • Oval symbol: start/stop symbol • Rectangle symbol: process symbol • Parallelogram: input/output symbol • Flowlines: connect symbols Programming with Microsoft Visual Basic 2005, Third Edition

  38. Coding the Clear Screen Button • xClearButton’s task: clear screen for next order • String: group of characters in quote marks (“”) • Zero-length string (empty string) • Pair of quote marks with nothing between them: “” • Two ways to remove control contents at runtime • Assign zero-length string to control’s Text property • Assign String.Empty to control’s Text property Programming with Microsoft Visual Basic 2005, Third Edition

  39. Coding the Clear Screen Button (continued) Figure 2-28: Pseudocode for the xClearButton’s Click event procedure Programming with Microsoft Visual Basic 2005, Third Edition

  40. Assigning a Value to a Property During Run Time • Assignment statement • Instruction assigning a value to an object at runtime • Syntax: [Me.]object.property=expression • Me refers to the current form (optional) • object and property are object and property names • expression contains the value to be assigned • Assignment operator (=): assigns value (right to left) Programming with Microsoft Visual Basic 2005, Third Edition

  41. Assigning a Value to a Property During Run Time (continued) Figure 2-32: Second assignment statement entered in the procedure Programming with Microsoft Visual Basic 2005, Third Edition

  42. Using the Focus Method • Method: a predefined procedure • Focus method • Allows you to move the focus to a specified control • Syntax: [Me.]object.Focus() • Object is the name of the control that receives focus Programming with Microsoft Visual Basic 2005, Third Edition

  43. Internally Documenting the Program Code • Comments: internal documentation • How to create a comment in Visual Basic 2005 • Place an apostrophe (‘) before a statement • The compiler ignores characters after apostrophe • Color of comments is different than color of code • Comments help make code readable Programming with Microsoft Visual Basic 2005, Third Edition

  44. Internally Documenting the Program Code (continued) Figure 2-33: Completed Click event procedure for the xClearButton Programming with Microsoft Visual Basic 2005, Third Edition

  45. Writing Arithmetic Expressions • Arithmetic expression • Contains arithmetic operators and operands • Precedence numbers • Indicate the order of operations in an expression • Order that operations are performed • From lower precedence number to higher number • Parentheses override default precedence Programming with Microsoft Visual Basic 2005, Third Edition

  46. Writing Arithmetic Expressions (continued) Figure 2-35: Most commonly used arithmetic operators and their order of precedence Programming with Microsoft Visual Basic 2005, Third Edition

  47. Writing Arithmetic Expressions (continued) • Unary operator: requires one operand; e.g., -7 • Binary operator: requires two operands • Associativity: orders operations at same level • Left to right for operations with same precedence • Integer division operator (\): • Divides two integers, returns an integer as a result • Modulus operator: returns a remainder Programming with Microsoft Visual Basic 2005, Third Edition

  48. Coding the Calculate Order Button • The Calculate Order button is responsible for: • Calculating total number of skateboards ordered • The total price of the order • Displaying results in two labels • Add instructions to button’s Click event procedure • Instructions are processed when user clicks button • Observe one problem: numbers treated as strings Programming with Microsoft Visual Basic 2005, Third Edition

  49. Coding the Calculate Order Button (continued) Figure 2-39: Code entered in the xCalcButton’s Click event procedure Programming with Microsoft Visual Basic 2005, Third Edition

  50. The Val Function • Function: predefined procedure • Performs a specific task and returns a value • Val function • Temporarily converts a string to a number • Returns the number • Syntax: Val(string): string will be treated as a number • Val corrects assignments in xCalcButton’s procedure Programming with Microsoft Visual Basic 2005, Third Edition

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