Chapter 2: Designing Applications

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Chapter 2 Designing Applications
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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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Solving the Problem Using a Procedure-Oriented
Approach

• Emphasis is on how to accomplish a task
• Flowchart
• Standardized symbols show problem-solving steps
• Pseudocode
• English phrases describing the required steps
• It is harder to write a complex application using
  procedure oriented approach

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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
• It is easier to write a complex application using
  an object oriented approach

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Solving the Problem Using an Object-Oriented
(OO) Approach (continued)?
Figure 2-4 Order screen created by the OO
application
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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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Creating an OO Application (continued)?
Figure 2-6 Processes used by a builder and a
programmer
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Identifying the Tasks, Objects and Events
Figure 2-11 Completed TOE chart ordered by object
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Drawing a Sketch of the User Interface
Figure 2-12 Vertical arrangement of the
Skate-Away Sales interface
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Drawing a Sketch of the User Interface
(continued)?
Figure 2-13 Horizontal arrangement of the
Skate-Away Sales interface
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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 controls BorderStyle property
• Add a text box to a form

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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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Preparing to Create the User Interface less is
more
Figure 2-14 Partially completed interface for
the Skate-Away Sales application
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Adding a Text Box Control to the Form
Figure 2-16 Form showing the correct location of
the City text box
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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

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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 controls caption
• Example CalculateOrder assigns C to button

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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

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Coding, Testing, Debugging, and Documenting the
ApplicationLesson C Objectives

• Code an application using its TOE chart
• Plan an objects 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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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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Coding the Application

• Code
• Coding
• TOE charts show which objects and events to code
• Use pseudocode or flowchart to design procedure

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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

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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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Coding the Clear Screen Button
Figure 2-28 Pseudocode for the xClearButtons
Click event procedure
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Assigning a Value to a Property During Run Time

• Assignment statement
• Instruction assigning a value to an object at
  runtime
• Syntax Me.object.propertyexpression
• 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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Assigning a Value to a Property During Run Time
(continued)?
Figure 2-32 Second assignment statement entered
in the procedure
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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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Internally Documenting the Program Code
(continued)?
Figure 2-33 Completed Click event procedure for
the xClearButton
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Writing Arithmetic Expressions
Figure 2-35 Most commonly used arithmetic
operators and their order of precedence
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Coding the Calculate Order Button
Figure 2-39 Code entered in the xCalcButtons
Click event procedure numbers are treated as
strings
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The Val Function

• Function predefined procedure that returns a
  value
• Val function
• Converts a string to a number
• Returns the number
• Syntax Val(string) string will be treated as a
  number
• Val corrects assignments in xCalcButtons
  procedure

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The Val Function (continued)?
Figure 2-42 Val function entered in the
xCalcButtons Click event procedure
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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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