Chapter 2: Designing Applications

Programming with Microsoft Visual Basic 2005, Third Edition

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

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

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

Solving the Problem Using an Object-Oriented (OO) Approach

(continued)

Figure 2-4: Order screen created by the OO application

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

Creating an OO Application (continued)

Figure 2-6: Processes used by a builder and a programmer

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

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?

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?

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

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

Identifying the Events (continued)

Figure 2-11: Completed TOE chart ordered by object

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

Drawing a Sketch of the User Interface (continued)

Figure 2-12: Vertical arrangement of the Skate-Away Sales interface

Figure 2-13: Horizontal arrangement of the Skate-Away Sales interface

• 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

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

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

Building the User InterfaceLesson B Objectives (continued)

• Lock the controls on the form

• Assign access keys to controls

• Use the TabIndex property

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

Preparing to Create the User Interface (continued)

Figure 2-14: Partially completed interface for the Skate-Away Sales application

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

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

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

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

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

Adding a Text Box Control to the Form (continued)

Figure 2-16: Form showing the correct location of the City text box

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

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

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

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

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

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

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

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

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

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

Coding the Clear Screen Button (continued)

Figure 2-28: Pseudocode for the xClearButton’s Click event procedure

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)

Assigning a Value to a Property During Run Time (continued)

Figure 2-32: Second assignment statement entered in the procedure

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

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

Internally Documenting the Program Code (continued)

Figure 2-33: Completed Click event procedure for the xClearButton

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

Writing Arithmetic Expressions (continued)

Figure 2-35: Most commonly used arithmetic operators and their order of precedence

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

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

Coding the Calculate Order Button (continued)

Figure 2-39: Code entered in the xCalcButton’s Click event procedure

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

The Val Function (continued)

Figure 2-42: Val function entered in the xCalcButton’s Click event procedure

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

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

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

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

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

Chapter 2: Designing Applications

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