TOE (Task, Object, Event) chart

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

• Follow the Windows standards regarding the layout and labeling of controls

Programming with Microsoft Visual Basic 2005, Third Edition 2

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



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 Interface

Lesson 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 Interface

Lesson 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


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 Application

Lesson 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 228: 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



(continued)

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



(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 239: 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 242: 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


TOE (Task, Object, Event) chart

Related documents

Products

Support

TOE (Task, Object, Event) chart

Related documents

Add this document to collection(s)

Add this document to saved

Suggest us how to improve StudyLib