vb.net introduction. .net framework.net framework class libraries: a large set of classes that forms...

VB.Net Introduction

.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

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.Net, J#, 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

Form

• Properties:– Name, FormBorder, Text, BackColor, BackImage,

Opacity• Events:

– Load, Closed• Rename a form (hard to rename):

– Change the name and text property.– Rename the form in the Solution Explorer.– Change the name in the code window.– Change the StartUp in the Project Property.

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 code.

• To refer to a property: – ControlName.PropertyName

– Ex. TextBox1.Text

Typical VB.Net Programming Tasks

• Creating 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 proceduresSum: textBox3.text=CStr(CDbl(textBox1.text)+CDbl(textBox2.text))Or (CDbl(textBox1.text)+CDbl(textBox2.text)).toString.Challenge: How to draw a horizontal line?.Demo: Text alignment

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

Variable Declarations• Option Explicit• 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 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#

• Note: ControlPanel/RegionalOptions/Date

• 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)

• Date data type format methods

Some Date Functions

• Now: Current date and time

• Today: Current date

• TimeOfDay

• DateDiff

• Demo– Days to Christmas– Date data type properties and methods

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 <40Text1.text=“cold”

CASE < 60Text1.text=“cool”

CASE 60 to 80Text1.text=“warm”

CASE ELSEText1.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 UntilPrivate Sub Command1_Click()Dim counter As Integercounter = 0Do While counter <= 5 Debug.write(counter) counter = counter + 1LoopText1.Text = counterEnd Sub

Private Sub Command2_Click()Dim counter As Integercounter = 0Do Until counter > 5 Debug.write(counter) counter = counter + 1LoopText1.Text = counterEnd 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– The address of the item is passed. Any changes

made to the passing variable are made to the variable itself.

• ByVal– Default– Only the variable’s value is passed.

ByRef, ByVal example

Private Sub Button1_Click()

Dim myStr As String

myStr = TextBox1.Text

Call ChangeTextRef (myStr)

TextBox1.Text = myStr

End Sub

Private Sub ChangeTextRef(ByRef strInput As String)

strInput = "New Text"

End Sub