Download - Chapter 2: Designing Applications Programming with Microsoft Visual Basic 2005, Third Edition
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Chapter 2: Designing Applications
Programming with Microsoft Visual Basic 2005, Third Edition
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2Programming 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
• Follow the Windows standards regarding the layout and labeling of controls
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3Programming with Microsoft Visual Basic 2005, Third Edition
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
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4Programming with Microsoft Visual Basic 2005, Third Edition
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
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5Programming with Microsoft Visual Basic 2005, Third Edition
Solving the Problem Using an Object-Oriented (OO) Approach
(continued)
Figure 2-4: Order screen created by the OO application
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6Programming with Microsoft Visual Basic 2005, Third Edition
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
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7Programming with Microsoft Visual Basic 2005, Third Edition
Creating an OO Application (continued)
Figure 2-6: Processes used by a builder and a programmer
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8Programming with Microsoft Visual Basic 2005, Third Edition
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
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9Programming with Microsoft Visual Basic 2005, Third Edition
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?
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10Programming with Microsoft Visual Basic 2005, Third Edition
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?
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11Programming with Microsoft Visual Basic 2005, Third Edition
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
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12Programming with Microsoft Visual Basic 2005, Third Edition
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
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13Programming with Microsoft Visual Basic 2005, Third Edition
Identifying the Events (continued)
Figure 2-11: Completed TOE chart ordered by object
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14Programming with Microsoft Visual Basic 2005, Third Edition
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
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15Programming with Microsoft Visual Basic 2005, Third Edition
Drawing a Sketch of the User Interface (continued)
Figure 2-12: Vertical arrangement of the Skate-Away Sales interface
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16Programming with Microsoft Visual Basic 2005, Third Edition
Drawing a Sketch of the User Interface (continued)
Figure 2-13: Horizontal arrangement of the Skate-Away Sales interface
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17Programming with Microsoft Visual Basic 2005, Third Edition
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
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18Programming with Microsoft Visual Basic 2005, Third Edition
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
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19Programming with Microsoft Visual Basic 2005, Third Edition
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
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20Programming with Microsoft Visual Basic 2005, Third Edition
Building the User InterfaceLesson B Objectives (continued)
• Lock the controls on the form
• Assign access keys to controls
• Use the TabIndex property
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21Programming with Microsoft Visual Basic 2005, Third Edition
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
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22Programming with Microsoft Visual Basic 2005, Third Edition
Preparing to Create the User Interface (continued)
Figure 2-14: Partially completed interface for the Skate-Away Sales application
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23Programming with Microsoft Visual Basic 2005, Third Edition
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
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24Programming with Microsoft Visual Basic 2005, Third Edition
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
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25Programming with Microsoft Visual Basic 2005, Third Edition
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
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26Programming with Microsoft Visual Basic 2005, Third Edition
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
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27Programming with Microsoft Visual Basic 2005, Third Edition
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
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28Programming with Microsoft Visual Basic 2005, Third Edition
Adding a Text Box Control to the Form (continued)
Figure 2-16: Form showing the correct location of the City text box
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29Programming with Microsoft Visual Basic 2005, Third Edition
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
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30Programming with Microsoft Visual Basic 2005, Third Edition
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
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31Programming with Microsoft Visual Basic 2005, Third Edition
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
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32Programming with Microsoft Visual Basic 2005, Third Edition
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
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33Programming with Microsoft Visual Basic 2005, Third Edition
Coding, Testing, Debugging, and Documenting the Application
Lesson 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
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34Programming with Microsoft Visual Basic 2005, Third Edition
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
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35Programming with Microsoft Visual Basic 2005, Third Edition
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
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36Programming with Microsoft Visual Basic 2005, Third Edition
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
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37Programming with Microsoft Visual Basic 2005, Third Edition
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
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38Programming with Microsoft Visual Basic 2005, Third Edition
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
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39Programming with Microsoft Visual Basic 2005, Third Edition
Coding the Clear Screen Button (continued)
Figure 2-28: Pseudocode for the xClearButton’s Click event procedure
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40Programming with Microsoft Visual Basic 2005, Third Edition
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)
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41Programming with Microsoft Visual Basic 2005, Third Edition
Assigning a Value to a Property During Run Time (continued)
Figure 2-32: Second assignment statement entered in the procedure
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42Programming with Microsoft Visual Basic 2005, Third Edition
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
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43Programming with Microsoft Visual Basic 2005, Third Edition
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
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44Programming with Microsoft Visual Basic 2005, Third Edition
Internally Documenting the Program Code (continued)
Figure 2-33: Completed Click event procedure for the xClearButton
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45Programming with Microsoft Visual Basic 2005, Third Edition
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
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46Programming with Microsoft Visual Basic 2005, Third Edition
Writing Arithmetic Expressions (continued)
Figure 2-35: Most commonly used arithmetic operators and their order of precedence
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47Programming with Microsoft Visual Basic 2005, Third Edition
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
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48Programming with Microsoft Visual Basic 2005, Third Edition
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
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49Programming with Microsoft Visual Basic 2005, Third Edition
Coding the Calculate Order Button (continued)
Figure 2-39: Code entered in the xCalcButton’s Click event procedure
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50Programming with Microsoft Visual Basic 2005, Third Edition
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
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51Programming with Microsoft Visual Basic 2005, Third Edition
The Val Function (continued)
Figure 2-42: Val function entered in the xCalcButton’s Click event procedure
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52Programming with Microsoft Visual Basic 2005, Third Edition
Using the Format Function to Format Numeric Output
• Format function: improves numbers display
• Syntax: Format(expression, style)
– Expression specifies number, date, time, or string
– Style: predefined or user defined format style
• Currency: example of a format style
– Displays number with a dollar sign and two decimal places
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53Programming with Microsoft Visual Basic 2005, Third Edition
Aligning The Text Within A Control
• TextAlign property– Specifies the position of the text within the control
• Using the TextAlign property in the order form– Center text contained in the xTotalBoardsLabel
and xTotalPriceLabel controls
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54Programming with Microsoft Visual Basic 2005, Third Edition
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: locating errors in the program • Errors can be related to either syntax or logic
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55Programming with Microsoft Visual Basic 2005, Third Edition
Assembling the Documentation
• Important documentation
– Planning tools
– Printout of application’s interface and code
• Your planning tools include:
– The TOE chart
– Sketch of the interface
– Flowcharts and/or pseudocode
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56Programming with Microsoft Visual Basic 2005, Third Edition
Summary – Lesson C
• 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