Introduction to VB.Net By William Lacktano.ppt

VB.Net Introduction
RCCS 307
BY W. LACKTANO

.NET Framework
• .NET Framework class libraries: A large set
of classes that forms the basis for objects
that can be used programmatically.
– Programming in the .NET Framework means
making use of the classes exposed by the
Framework, building your own classes on top
of these and manipulating the resulting objects.
• Creating Internet applications and Windows
applications

Class and Object
• A class is a blueprint from which objects
are made. Every object created from a
class is an instance of the class.
• Properties and methods: An object’s
interface consists of properties and
methods. A property is an attribute
associated with an object, while a method is
an action that the object can carry out.

VB.NET is Object-Oriented
• Everything from the simplest data types
provided by VB to the complex windows is
a class.
– Ex:
• Dim iNum as Integer
• iNum=10
• Debug.WriteLine (“The number is: “ &
iNum.ToString)

Visual Studio .NET
• It is the development environment for creating
applications based on the .NET Framework.
• It supports VB, C#, and C++.
• Demo:
– Start page: MyProfile
– Starting project: Project types, name and location,
– Solutions and projects, renaming a project, property
page, AutoHide, Dock/Float
– Configure start up environment: Tools/Option
– View/Solution, View/Class, Project/Add Windows
Form, Project/Add New Item
– Form, Code view, File Properties and Object properties

Introduction to Visual Basic .Net
• Event-driven programming
– The interface for a VB program consists of one
or more forms, containing one or more controls
(screen objects).
– Form and control has a number of events that it
can respond to. Typical events include clicking
a mouse button, type a character on the
keyboard, changing a value, etc.
– Event procedure

Typical VB.Net Controls
• TextBox
• Label
• Button
• CheckBox
• RadioButton
• ListBox
• ComboBox
• PictureBox

Text Box
• Properties:
– AutoSize, BorderStyle, CauseValidation, Enabled,
Locked, Multiline, PasswordChar, ReadOnly,
ScrollBar, TabIndex, Text, Visible, etc.
• Properties can be set at the design time or at the
run time using codes.
• To refer to a property:
– ControlName.PropertyName
– Ex. TextBox1.Text

Typical VB.Net Programming
Tasks
• Creatin g the GUI elements that make up
the application’s user interface.
– Visualize the application.
– Make a list of the controls needed.
• Setting the properties of the GUI elements
• Writing procedures that respond to events
and perform other operations.

Demo
Num1
Num2
Sum =
Control properties
Event: Click, MouseMove, FormLoad, etc.
Event procedures
Sum:
textBox3.text=CStr(CDbl(textBox1.text)+CDbl(textBox2.text))
Or (CDbl(textBox1.text)+CDbl(textBox2.text)).toString
Challenge: How to draw a horizontal line?

VB Projects
• A VB project consists of several files. Visual
Studio .Net automatically creates a project folder
to keep all project files in the folder.
– Solution file
– Project file
– Form file
– Modules
– Class file
– Etc.

Configure VB Project
• Project property page
– General
– Build: Option Explicit
– Imports
• Debug
– Debug/Windows

Introductory VB Topics
• Declaring variables: Option Explicit
– DIM, PUBLIC, PRIVATE, STATIC, CONST
– Boolean, Integer, Long, Single, Double, Date,
String
– Ex: DIM dblIntRate As Double
– Ex: Dim X As Integer, Y As Single
– Ex: Dim A, B, C As String
– Ex: Dim X AS Integer = 25
– Ex: CONST Maximum As Integer = 100

Variable Declarations
• Dim variableName as DataType
• Variable naming rules:
– The first character must be a letter or an underscore
character.
– Use only letters, digits, and underscore.
– Cannot contain spaces or periods.
– No VB keywords
• Naming conventions:
– Descriptive
– Consistent lower and upper case characters.
• Ex. Camel casing: lowerUpper, employeeName

Control Naming Conventions
• The first three letters should be a lowercase prefix
that indicates the control’s type.
– frm, txt, lbl, btn.
• The first letter after the prefix should be
uppercase.
– txtSalary, lblMessage
• The part of the control name after the prefix
should describe the control’s purpose in the
application.

VB Data Types
• Boolean (True/False): 2 bytes
• Byte: Holds a whole number from 0 to 255.
• Char: single character
• Date: date and time, 8 bytes.
• Decimal: Real number up to 29 significant digits, 16 bytes
• Double: real, 8 bytes
• Single: real, 4 bytes
• Integer: 4 bytes (int32, uint32)
• Long: 8 bytes integer
• Short: 2 bytes integer
• String
• Object: Holds a reference of an object

Variable Declaration Examples
• Dim empName as String
• Declare multiple variables with one Dim:
– Dim empName, dependentName, empSSN as String
• Dim X As Integer, Y As Single
• Initiatialization
– Dim interestRate as Double = 0.0715

Variable Default Value
• Variables with a numeric data type: 0
• Boolean variables: False
• Date variables: 12:00:00 AM, January 1 of
the year 1.
• String variables: Nothing

Object Reference
• Declare object variales:
– Dim varName As Classname
– varName = New Classname()
– Or: Dim varName As New Classname()
• Dereferencing objects:
– varName = Nothing

Variable Scope
• Block-level scope: declared within a block of code
terminated by an end, loop or next statement.
– If city = “Rome” then
• Dim message as string = “the city is in Italy”
• MsgBox(message)
– End if
• Procedural-level scope: declared in a procedure
• Class-level, module-level scope: declared in a
class or module but outside any procedure with
either Dim or Private keyword.
• Project-level scope: a class or module variable
declared with the Public keyword.

Data Conversion
• Implicit conversion: When you assign a value of
one data type to a variable of another data type,
VB attempts to convert the value being assigned to
the data type of the variable if the OptionStrict is
set to Off.
• Explicit conversion:
– VB.Net Functions: CStr, Ccur, CDbl, Cint, CLng,
CSng, Cdate,Val, etc.
– .Net System.Convert
• Type class’s methods:
– toString

Date Data Type
• Variables of the Date data type can hold both a
date and a time. The smallest value is midnight
(00:00:00) of Jan 1 of the year 1. The largest
value is 11:59:59 PM of Dec. 31 of the year 9999.
• Date literals: A date literal may contain the date,
the time, or both, and must be enclosed in #
symbols:
– #1/30/2003#, #1/31/2003 2:10:00 PM#
– #6:30 PM#, #18:30:00#

• Date Literal Example:
– Dim startDate as dateTime
– startDate = #1/30/2003#
• Use the System.Convert.ToDateTime
function to convert a string to a date value:
– startDate = System.Convert.ToDateTime(“1/30/2003”)
– If date string is entered in a text box:
• startDate = System.Convert.ToDateTime(txtDate.text)
• Or startDate=Cdate(txtDate.text)

Arithmetic and String Operators
• +, -, *, /. , ^
• String Concatenation: &, +
• Compound operator:
: X= X+1 or X +=1

IF Statement
• IF condition THEN
statements
[ELSEIF condition-n THEN
[elseifstatements]
[ELSE
[elsestatements]]]
End If

Select Case Structure
• SELECT CASE testexpression
[CASE expressionlist-n
[Statements]
[CASE ELSE
[elsestatements]
END SELECT

Select Case Example
• SELECT CASE temperature
CASE <40
Text1.text=“cold”
CASE 40 to 60
Text1.text=“cool”
CASE 60 to 80
Text1.text=“warm”
CASE ELSE
Text1.text=“Hot”
End Select

Loop
• FOR index – start TO end [STEP step]
[statements]
[EXIT FOR]
NEXT index
DO [{WHILE| UNTIL} condition]
[statements]
[EXIT DO]
LOOP

Do While/Do Until
Private Sub Command1_Click()
Dim counter As Integer
counter = 0
Do While counter <= 5
Debug.Print counter
counter = counter + 1
Loop
Text1.Text = counter
End Sub
Dim counter As Integer
counter = 0
Do Until counter > 5
Debug.Print counter
counter = counter + 1
Loop
Text1.Text = counter
End Sub

With … End With
With TextBox1
.Height = 250
.Width = 600
.Text = “Hello”
End With
Convenient shorthand to execute a series of
statements on a single object. Within the block,
the reference to the object is implicit and need
not be written.

Procedures
. Sub procedure:
Sub SubName(Arguments)
…
End Sub
– To call a sub procedure SUB1
• CALL SUB1(Argument1, Argument2, …)

Function
• Private Function tax(salary) As Double
• tax = salary * 0.1
• End Function
– Or
• Private Function tax(salary)
• Return salary * 0.1
• End Function

Call by Reference
Call by Value
• ByRef
– Default
– The address of the item is passed. Any changes
made to the passing variable are made to the
variable itself.
• ByVal
– Only the variable’s value is passed.

ByRef, ByVal example
Dim myStr As String
myStr = TextBox1.Text
ChangeTextRef (myStr)
TextBox1.Text = myStr
End Sub
Private Sub ChangeTextRef(ByRef strInput As
String)
strInput = "New Text"
End Sub

Introduction to VB.Net By William Lacktano.ppt

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