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MS Visual Basic 6

Walter Milner


2/15

VB 6 0 Introduction

background to VB, A hello World program

1 Core language 1 Projects, data types, variables, forms, controls , a calculator program

2 Core language 2 Conditional statements, exception handling, loops, arrays, debugging

3 Core language 3 Functions, sub-routines, parameter passing, modules, scope, lifetime

4 Controls scrollbar, radio buttons, checkboxes, listboxes, timers, control arrays

5 Graphics primitives and image files

6 Forms Forms MDI, menus

7 Files and databases adding controls, using data files, using databases

8 Deployment


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Hello World in VB Start VB

New Project Standard .exe Click the Button control on the ToolBox

and drag in the form

Double click the new button to invokethe code editor

Enter code:

Click the Run button

Private Sub Command1_Click()

MsgBox ("Hello world")

End Sub

Exercisetry this out


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What is Visual Basic?

Kemeny and Kurtz DartmouthCollege 1964

For students simple interpreted

Many versions since MS VB versions more power

not so simple

VBScript VBA .NET framework

RAD especially of user interface


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A very early version


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VB is not..

Vendor independent

Platform independent

Based on a constant language definition

Separated definition and IDE implementation

Well documented

(IMO) suitable for very large projects which must

be maintained over a long period of time


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VB is .. easy to use

suitable for RAD very marketable


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Building an application - steps

Commercial data driven waterfall

model project management

Science/engineering underlying data and

physical model, algorithms, testing

In VB RAD focus on user interface

prototyping and review.


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Building an application - forms

VB uses 'form' to mean Window

Info on form stored in a .frm file

VB system draws form based on that info Forms can be treated like classes in OOP

- later


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Building an application - controls

Buttons, text boxes, labels, check boxes..

VB 'control' = user interface widget

Some invisible timer

Controls have properties eg backgroundcolor

Three kinds

standard non-standard MS controls (common dialog, tab)

and 3rdparty

ActiveX controls written in-house


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Building an application - modularity

Spaghetti programming, structuredprogramming, OOP = increasing modularity

In VB application constructed from modules

= files in project- Form modules

BASIC modules

Class modules Privateand publiccontrol interaction

between modules


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Building an application - objects

Some OOP in VB not pure OOP

objects = things eg a form

class = type of object eg a form design property = data value associated with

object

method = something the object can do


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Building an application example of OOP

Dim f As Form2

Set f = New Form2

f.Show

f.BackColor = RGB(255, 0, 0)

Form2 is a class

f is an objectan instanceof

class Form2

the Form2 class has amethodcalled show

It has a propertycalled

BackColor


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Event-driven programming

Standard approach for GUIs

Contrast with old character interfaces programdetermines what happens

In GUI, the user triggers what application does(mostly)

Eventexamples are key press, mouse move, timertimeouts

Correspond to native Windows Messages (next

slide) Event handler = a subroutine which will execute

when that event happens


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Windows Messages Spy++

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