Tutorial 21 Procedure-Oriented vs Object- Oriented/Event-Driven Procedure-oriented Emphasis of a...

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Procedure-Oriented vs Object-Oriented/Event-Driven

Procedure-orientedEmphasis of a program is on how to accomplish a task

User has little, if any, control

Object-oriented/Event-drivenEmphasis of a program is on the objects included in the interface and the events that occur on those objects

User has a lot of control

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Architect vs ProgrammerPlan the home (blueprint)

Build the frame

Complete the home

Inspect the home and fix any problems

Assemble the documentation

Plan the application (TOE chart)

Build the user interface

Code the application

Test and debug the application

Assemble the documentation

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Step 1 - Plan the Application

Identify the tasks the application needs to perform

Identify the objects to which you will assign those tasks

Identify the events required to trigger an object into performing its assigned task

Draw a sketch of the user interface

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Identify the Application’s Tasks

What will the user need to enter?

What will the application need to calculate?

What will the application need to display (screen) and/or print (printer)?

How will the user end the application?

Will previous information need to be cleared from the screen?

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Sample TOE Chart

Task Object Event

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GUI Design Tips - 1

Organize the user interface so that the information flows either vertically or horizontally, with the most important information always located in the upper-left corner of the screen

Group related controls together using either white space or a frame

Align controls to minimize number of margins

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GUI Design Tips - 2

Either center the command buttons along the bottom of the screen or stack them in either the upper-right or lower-right corner

Use no more than six command buttons on a screen

Place the most commonly used command button first

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GUI Design Tips - 3

Assign meaningful captions to command buttons

Place the caption on one line and use from one to three words only

Use book title capitalization for command button captions

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GUI Design Tips - 4

Label each control in the interface. The label should be from one to three words only, and it should be entered on one line

Align each label on the left, and position each either above or to the left of the control it identifies

Follow the label with a colon (:) and use sentence capitalization

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Step 2 - Build the User Interface

Use the sketch you drew during the Planning step

Follow the GUI design guidelines

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More GUI Design Tips - 1

Maintain a consistent margin of two or three dots from the edge of the window

Position related controls on succeeding dots. Controls that are not part of any logical grouping may be positioned from two to four dots away from other controls

Try to create an interface that no one notices

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More GUI Design Tips - 2

Command buttons in the interface should be sized relative to each other

If the command buttons are centered on the bottom of the screen, then each button should be the same height; there widths, however, may vary

If the command buttons are stacked in a corner, then each should be the same height and the same width

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More GUI Design Tips - 3

The human eye is attracted to pictures before text, so include a graphic only if it is necessary to do so

If you are including the graphic for aesthetics only, use a small graphic and place it in a location that will not distract the user

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More GUI Design Tips - 4

Use 8, 10, or 12 point fonts for the elements in the user interface

Use only one or two font sizes

Use a sans serif font for the text

Use only one font type for all of the text

Avoid italics and underlining

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More GUI Design Tips - 5

The human eye is attracted to color before black and white

Build the interface using black, white, and gray first, then add color only if you have a good reason to do so

Use either white, off-white, light gray, pale blue, or pale yellow for an application’s background, and use black for the text

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More GUI Design Tips - 6

Always use dark text on a light background because it is the easiest to read

Never use a dark color for the background or a light color for the text

Limit the number of colors (other than white, black, and gray) to three

Never use color as the only means of identification for an interface element

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More Properties

BackStyle—determines whether the label is transparent or opaque

BorderStyle—determines the style of the object’s border

Appearance—determines if the control appears flat or three-dimensional

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Caption vs Text

Text box controls have a Text property

Forms and label controls have a Caption

property

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TabIndex Property

Determines the order in which a control receives the focus when the user is using the Tab key to tab through the controls in the interface

The value of the TabIndex property for the first control placed on a form is 0

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Access KeysAllows the user to select an object using the Alt key in combination with a letter or number

Assign an access key to each of the essential elements in the interface

Mouse may be inoperative

Accommodate fast typists

Accommodate people with disabilities

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More on Access KeysEach access key must be unique

You can assign an access key to any control that has a Caption property

Place an & to the left of the desired letter in the Caption property

To give keyboard access to a text box, assign an access key to its identifying label, then set the label’s TabIndex value to one less than the text box’s TabIndex value

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Step 3 - Code the Application

Use pseudocode to help you plan the code

Internally document the code by placing an apostrophe before the comment in the Code window

Print Order button1. Hide the 4 command buttons

2. Print the form

3. Display the 4 command buttons

4. Send the focus to the Clear Screen button

‘hide the command buttons

<code>

‘print the form

<code>

‘display the command buttons

<code>

‘set the focus

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Assignment Statement

Use to assign a value to a property.

[form.]object.property = value

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Operator Order of Precedence^ exponentiation

- negation

*, / multiplication and division

\ integer division

Mod modulus arithmetic

+, - addition and subtraction

You can use parentheses to override the order or precedence.

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Function

A predefined Visual Basic procedure

A function returns a value

Val and Format are two examples of Visual Basic’s intrinsic functions

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Val Function

Val function - returns the numeric equivalent of a string

Syntax: Val(string)This Val function: Would be converted to:

Val(“456”) 456

Val(“24,500) 24

Val($56.88) 0

Val(“A”) 0

Val(“”) 0

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Translating Pseudocode into a Visual Basic Equation

Total skateboards = blue skateboards + yellow skateboards

lblTboards.Caption = Val(txtBlue.Text) + Val(txtYellow.Text)

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Format FunctionFormat function - returns a formatted expression

Syntax: Format(expression, format)

Some of Visual Basic’s predefined formats:

Currency

Fixed

Standard

Percent

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MethodLike a function, a method is a predefined Visual Basic procedure. Unlike a function, a method does not return a value

PrintForm method - prints the form during run time

Syntax: [form.]PrintForm

SetFocus method - allows you to move the focus to a specified control or form while the application is running

Syntax: [form.]object.SetFocus

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Form Properties

BorderStyle

ControlBox

MaxButton

MinButton

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Step 4 - Testing and Debugging

Test with both valid and invalid data

Debugging refers to the process of locating errors in the program

Syntax errortyping PrntForm rather than PrintForm

Logic error calculating the net pay before calculating the state income tax

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Step 5 - Assemble the Documentation

Place your planning tools and a printout of the application in a safe place

Your planning tools include the TOE chart, sketch of the interface, and either the flowcharts or pseudocode

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Debugging Technique

Always use the Val function in equation

that include either the Text property or

the Caption property. The Val

function tells Visual Basic to treat these

properties as numbers rather than as

strings