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Advanced web technologies - 12261

Book1 contains VB.net part

Modules of Book 1 Slide No.
Module 1 : Introduction to Basic Windows programming using VB.net 2
Module 2 : Programming Concepts 17
Module 3: Streams And Files 71
Module 4 : Exception Handling 80
Module 5 : OO Programming Concepts 97
Module 6 : Namespaces 111
Module 7: Accessing Data with .Net 139
Module 8: Multi threading - Concept and Program 170

Book 2 contains ASP.net part
compiled by RJ , 9892544177 1

Module 1: Introduction to Basic Windows programming using VB.net

Short note on development/ history of VB.net( 4m)

Microsoft has developed many languages before reaching to the .NET
framework:
1964 – BASIC
Prob : no support for UI
1975 – QBASIC
Prob : slow response time
1976 – VB 1.0 , the series progressed uptill VB 5.0 ( 1997)
Adv : Allowed good UI development , component library to share code.
Library files are in .dll format.
2000 – VB 6.0
Prob : lots of garbage code due to garbage collection.
Viva Q : what is Garbage collection?

Therefore, finally a new and clean implementation developed =
.NET framework.

What is .NET ?


Coding the First Visual Basic .Net Application with out
using IDE

1. Open notepad. Create a new file save as
“step1.vb”
2. Type the following code in step1.vb file

Imports System // predefined package in the .NET framework

Public Class Step1
Shared Sub Main()
System.Console.WriteLine(“We are engineering students”)
End Sub

End Class


3. launch the command prompt from
Start, Programs, Microsoft Visual Studio .NET 7.0, Visual Studio .NET Tools menu.

4. (To test the vb.net compilier is running or not)
Before you compile at the command prompt, type vbc and press Enter

5.o/p is
Microsoft (R) Visual Basic.NET Compiler version 7.00.9254
for Microsoft (R) .NET CLR version 1.00.2914.16
Copyright Microsoft Corp 2001. All rights reserved.
Visual Basic Compiler Options


Viva : why type vbc ?
To check the following
• Visual Basic.NET installed
• We have the appropriate permission to run the compiler
• The system was able to find the file vbc.exe. ie vb compiler

6. Compile and make exe
C:TYVBC1>vbc step2.vb /t:exe
Microsoft (R) Visual Basic.NET Compiler version 7.00.9254
for Microsoft (R) .NET CLR version 1.00.2914.16
Copyright Microsoft Corp 2001. All rights reserved.

7. Run the executable
C:TYVBC1>step2
We are engineering students


What are command line switches? ( 4m )

Command line switches are used to configure the output according to
application requirement.
Eg. Of switches are
3. /target or /t : < winexe or exe or library or module>

8. /out : < filename >

11. /help ( or /?)


List different components of IDE and its use? (4m)
Before we begin with the using the IDE we must set the profile. Choose
profile
”VB developer Profile”.
The main components are :
Toolbox : has window controls, common controls, containers, menus
and toolbars, data , components, printing, Dialogs, WPF
interoperability, reporting, Vb power packs.
Command / immediate window.
Server explorer : contains all data base components, used only when
we have SQL or Ms Access .
Solution explorer : all forms , its GUI components.
The development area, where the Form appears.


Create a simple form (window application). The application must accept
name and phone_number.

The name field must raise an exception when the numeric is entered or it is
left blank. Similarly validate the phone_no field.

Step 1: Create the project
Using the menus, choose the File, New, Project command, bringing up the New
Project dialog. Select the Windows Application icon and change the project
name from WindowsApplication1 to name_phno. (name_phno.vb)

Step 2: Develop the User- Interface.

Step 3: logic : “Raising an exception” means using validating or validated event
on the textbox where the user would enter the name and phone no.
Sub TextBox1_Validating(… )
Sub TextBox2_Validating (… )
Viva Q : difference between validating and validated event.
Validating checks for input moment we enter data. Validated checks only after we leave
the field and go to the next field.
9
compiled by RJ , 9892544177

Use ErrorProvider control to report an error message.

If TextBox1.Text = "" Then
ErrorProvider1.SetError(TextBox1, "plz enter a name")
e.Cancel = True Indicates that the
Else error control
If IsNumeric(TextBox1.Text) Then should be shown.
ErrorProvider1.SetError(TextBox1, "plz enter a correct name")
e.Cancel = True
Else
ErrorProvider1.SetError(TextBox1, "")
End If
End If

Apply similar logic with textbox2.

Step 4: Running the project : press play button or F5.


Coding steps
ErrorProvider1.SetError(TextBox1, "") -

Private Sub Button1_Click(ByVal sender As Object,
ByVal e As System.EventArgs) Handles ?
Handles Button1.Click
End
End Sub Viva : difference
between end and exit

Sub Form1_Load (ByVal sender As System.Object,
ByVal e As System.EventArgs)
Handles MyBase.Load


Create a simple login having 2 textboxes – username and password.
Password must have “vesp” as input only. Provide 2 buttons “submit ”
and “exit”. Allow maximum 3 login attempts.

Step 1 : choose window application and create the UI as reqd.

Step2 : logic :
Both text boxes i.e the Username and password must have some data.
If TextBox1.Text = "" Or TextBox2.Text = "" Then
MsgBox("enter all fields")

No restriction on data entered in Username field – Textbox1

Check data entered in textbox2 = “vesp” or not.
If TextBox2.Text = "vesp" Then
MsgBox("login successfull")


Maximum 3 attempts indicates set up a counter variable

All validation must be done on “Submit button” , so put the code in
Sub Button1_Click(ByVal sender As Object,
ByVal e As System.EventArgs)

Every textbox experiences TextBox1_TextChanged event when we
give input. We need not handle it , as the logic is not asking for any
validation on typing.

Assignment “: Develop application to validate for numeric input on
typing. Handle TextBox1_TextChanged event.


Create a window application to calculate SI. It should
accept P, N and R as inputs. Raise exception if no input or
text is entered.

Step 1: Create a window application. Develop the UI.
Step 2: logic :
Sub TextBox1_Validating(ByVal sender As Object, ByVal e As
System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
If TextBox1.Text = "" Then Blank not allowed
ErrorProvider1.SetError(TextBox1, "enter an amount")
e.Cancel = True
Else
If IsNumeric(TextBox1.Text) Then No numbers
allowed
ErrorProvider1.SetError(TextBox1, "")
Else
ErrorProvider1.SetError(TextBox1, "enter an correct amount")
e.Cancel = True
End If
End If

Logic of PNR / 100 to find SI is implemented on click of a button.

Sub Button1_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button1.Click

MessageBox.Show(((TextBox1.Text * TextBox2.Text *
TextBox3.Text) / 100))

end sub


Create a window application which highlights the
importance of validating event over validated.

Step 1: Create Window application with 2 textboxes.

Step2 : logic :
On Textbox 1 handle validated event.
On Textbox 2 handle validating event.

Sub TextBox1_Validated(ByVal sender As Object, ByVal e As
System.EventArgs) Handles TextBox1.Validated

Sub TextBox2_Validating(ByVal sender As Object, ByVal e As
System.ComponentModel.CancelEventArgs) Handles TextBox2.Validating


Module 2: Programming Concepts
> Variable types
> Built –In functions
> String functions
> Console Based programming.

Q> List with ranges the different types of variables supported by
VB.NET. ( 4m )

VARIABLES: Defn : A temporary storage location.

5. Integer
6. Numbers with Decimal Places
7. Strings and Characters
8. Boolean
9. Date

Data Type ( integer) Size (Bytes) Range

Byte 1 0 to 255

Short 2 -32,768 to 32,767

Integer 4 -2,147,483,648 to
2,147,483,647

Long 8 –9,223,372,036,
854,775,808, 9,223,372,036,
854,775,807


Data Type ( number with decimal places) Size (Bytes) Range

Single 4 –3.402823 × 10^38
to –1.401298 × 10^–45

Double 8 for negative numbers;
1.401298 × 10^–45
to 3.402823 × 10^38
for positive numbers
–1.797693134
86231 × 10^308 to
–4.940656458
41247 × 10^–324
for negative numbers;
4.940656458
41247 × 10^–324 to
1.797693134
86232 × 10^308 for
positive numbers


Data Type Size (Bytes) Range

Char 2 One character
String 10+2 Up to 2
Per billion
character characters

Data Type Size (Bytes) Range

Boolean 2 True or False

Date 8 January 1, 100 to December
31,9999


Declaring Variables
Dim sFirstName As String

Dim dblGrossDomesticProduct As Double

Dim bLearned As Boolean

Dim dtDateOfMagnaCartaSigning As Date = #DEC 15,
2010#

Dim lPeopleOnEarth As Long = 6000000000


WAP to declare 3 arrays of integer, date and string type resp.
demonstrate different ways of initialing the array . ( 4m )
– Refer pg 14 of notes

1 ‘Simple declaration
2 Dim iValues(3) As Integer // note no ; at end
3 Dim dtDates() As Date
4 Dim I As Integer

5 For I = 1 To 3 // 1st way of init an array.
6 iValues(I-1) = I
7 Next


8 ‘Changing the size of an existing array
9 ReDim dtDates(4)
10 ‘fill the list of dates of sem 6 TT
11 dtDates(0)=”4/24/2011” ‘management // 2nd way of initzn
12 dtDates(1)=”4/27/2011” ‘s/w testing or DCNE
13 dtDates(2)=”5/03/2011” ‘AJP
7 dtDates(3)=”5/06/2011” ‘AWT

15 ‘Declaration with Initialization
16 Dim sMonths() As String = {“Jan”,”Feb”,”Mar”,”Apr”,”May”,”Jun”, _
• “Jul”,”Aug”,”Sep”,”Oct”,”Nov”,”Dec”} // 3rd way of initzn

18 ‘Using arrays
14 Console.WriteLine(“”)

20 Console.WriteLine(“Second value in iValues = {0}”, iValues(1))
21 Console.WriteLine(“Third date in dtDates = {0}”, dtDates(2))
22 Console.WriteLine(“Eleventh month of the year = {0}”, sMonths(10))


Constants
Constants are declared using one of the two
forms

Const PI = 3.1415 As Double

Const DSN As String = “Random”


BUILT-IN FUNCTIONS Refer awt pracs > variables

Function Description

CBool Converts to a Boolean. Anything that evaluates to False or 0 will be set to False; otherwise, it will be True.

CByte Converts to a Byte. Any value greater than 255, or any fractional information,will be lost.

CChar Converts to a single character. If the value is greater than 65,535, it will be lost. If you convert a String, only
the first character is converted.

CDate Converts to a Date. One of the more powerful conversion functions, CDate can recognize some of the more
common formats for entering a date.

CDbl Converts to a Double.

CInt Converts to an Integer. Fractions are rounded to the nearest value.

CLng Converts to a Long. Fractions are rounded to the nearest value.

CSht Converts to a Short. Fractions are rounded to the nearest value.

CStr Converts to a String. If the value is a Date, this will contain the Short Date format.

CType Converts to any type. This is a powerful function that enables you to convert any data type into any other
type. Therefore, the syntax for this function is slightly different than the others.


Syntax of CType( )

oNewVariable = CType(oOldVariable, NewType)

In which oNewVariable and oOldVariable are placeholders for the
variables that we’re converting to and from, respectively. NewType
is the type you are converting to.

Eg : convert object of customer to employee.
Dim oCust As Customer = New Customer ( “a”, “b”)
Dim oEmp As Employee = New Employee ( “c”, “d”)
// here assuming that the no. and type of attributes is the same In both
the classes.
Then oEmp = CType( oCust, Employee ) ‘ converts


Example : uses the CBool function to convert expressions to Boolean
values. If an expression evaluates to a nonzero value, CBool returns
True; otherwise, it returns False.

Example : uses the CByte function to convert an expression to a Byte.


Example: uses the CChar function to convert the first character of a String
expression to a Char type.

The input argument to CChar must be of data type Char or String. You cannot use CChar to
convert a number to a character, because CChar cannot accept a numeric data type. The
following example obtains a number representing a code point (character code) and converts
it to the corresponding character. It uses the InputBox function to obtain the string of digits,
CInt to convert the string to type Integer, and ChrW to convert the number to type Char.


Example: uses the CDate function to convert strings to Date values.

Example of Cdbl


Example of Clng() function

Example : uses the CObj function to convert a numeric value to Object. The
Object variable itself contains only a four-byte pointer, which points to the
Double value assigned to it.


CSng Example

Example: uses the CStr function to convert a numeric value to String.


Example: uses the CStr function to convert Date values to String values.
Or short note on CStr()

CStr always renders a Date value in the standard short format for the current locale, for
example, "6/15/2003 4:35:47 PM". However, CStr suppresses the neutral values of 1/1/0001
for the date and 00:00:00 for the time.

Date/Time Conversions. Use the IsDate function to determine if a value can be converted to a
date and time. CDate recognizes date literals and time literals but not numeric values. To
convert a Visual Basic 6.0 Date value to a Date value in Visual Basic 2005 or later versions,
you can use the DateTime.FromOADate method.

String Manipulation Functions : The following table lists the functions
that Visual Basic provides to search and manipulate strings.


Example : uses the UCase function to return an uppercase version of a string.

Example : uses the LTrim function to strip leading spaces and the RTrim
function to strip trailing spaces from a string variable. It uses the Trim
function to strip both types of spaces.

Refer awt pracs > Console Application3

35

Example: uses the Mid function to return a specified number of characters from
a string.

Example : uses Len to return the number of characters in a string.


Example: uses the InStr function to return the position of the first occurrence
of one string within another.


Home Assignment
A> Specify the string functions which would
1> Check len of the sPassword .
2> if sPassword is containing “ Engineering students” find the postn of
string “students”.
Hint : be case sensitive
Stringdemo.vb


How to develop a Console Based application.

Select File > New > Project > Console application.

Eg : A simple console Application which reads 5 integers and calculates
average. Print the average number.

Refer exp4 > Module2.vb

Readline() and writeline() functions are predefined in
NameSpace = Systems.console

Eg : Make a console application and accept input via InputBox.



Develop console application for showing different date and time formats.
Dateformatspecifiers.vb

Refer > console Application 1


Programming user-defined Routines or Functions

There are 2 types of procedures
Subroutine ( or sub in coding )
Function

Sub does not return any value

1 Sub ShowMessage(ByVal Message As String)
2 Console.WriteLine(Message)
3 End Sub
4 ShowMessage(“Hello World from Visual Basic .NET”)


Eg. Of function
Function returns some value
1 Private Function GetValue(ByVal Prompt As String) As String
2 Console.Write(Prompt)
3 Return Console.ReadLine
5 End Function

Analysis :

Develop a console based application showing how to interchange or swap numbers.
Define a sub or function to swap.



Define scope of a Variable. Describe it with all details.
The scope of a declared element is the set of all code that can refer to it
without qualifying its name or making it available through an
Imports Statement (.NET Namespace and Type). An element can have
scope at one of the following levels:

These levels of scope progress from the narrowest (block) to the widest (namespace), where
narrowest scope means the smallest set of code that can refer to the element without
qualification.


Specify the scope of an element when you declare it. The scope can
depend on the following factors:
• The region (block, procedure, module, class, or structure) in which
you declare the element
• The namespace containing the element's declaration
• The access level you declare for the element

Block Scope
A block is a set of statements enclosed within initiating and terminating
declaration statements, such as the following:

Do and Loop
For [Each] and Next
If and End If
Select and End Select
SyncLock and End SyncLock
Try and End Try
While and End While
With and End With


The scope of the integer variable cube is the
block between If and End If, and you can no
longer refer to cube when execution passes
out of the block.

Note : Even if the scope of a variable is limited to a block, its lifetime is still that of
the entire procedure. If you enter the block more than once during the procedure,
each block variable retains its previous value.

Procedure scope :
An element declared within a procedure is not available outside that procedure. Only the
procedure that contains the declaration can use it. Variables at this level are also known as
local variables. You declare them with the Dim Statement (Visual Basic), with or without the
Static (Visual Basic) keyword.

Procedure and block scope are closely related. If you declare a variable inside a procedure
but outside any block within that procedure, you can think of the variable as having block
scope, where the block is the entire procedure.

Module Scope
• The single term module level applies equally to modules, classes, and structures.
You can declare elements at this level by placing the declaration statement outside of
any procedure or block but within the module, class, or structure.
• When you make a declaration at the module level, the access level you choose
determines the scope. The namespace that contains the module, class, or structure
also affects the scope.

Refer awt pracs > ScopeVar


Namespace Scope
If you declare an element at module level using the Friend (Visual Basic) or
Public (Visual Basic) keyword, it becomes available to all procedures throughout
the namespace in which the element is declared.

Public strMsg As String


• Namespace scope includes nested namespaces. An element available from
within a namespace is also available from within any namespace nested
inside that namespace.

• If your project does not contain any Namespace Statements, everything in
the project is in the same namespace. In this case, namespace scope can
be thought of as project scope. Public elements in a module, class, or
structure are also available to any project that references their project.

Access level or Visibility Modifiers applicable to variables

1. Public or Friend variables
2. Private or local variables
3. Protected – only used during Inheritance.
4. Shared
5. Static


Advantages of Local Variables
• Local variables are a good choice for any kind of temporary calculation, for the
following reasons:
• Name Conflict Avoidance. Local variable names are not susceptible to conflict.
For example, you can create several different procedures containing a variable
called intTemp. As long as each intTemp is declared as a local variable, each
procedure recognizes only its own version of intTemp. Any one procedure can
alter the value in its local intTemp without affecting intTemp variables in other
procedures.
• Memory Consumption. Local variables consume memory only while their
procedure is running. Their memory is released when the procedure returns to
the calling code. By contrast, Shared (Visual Basic) and Static (Visual Basic)
variables consume memory resources until your application stops running, so
use them only when necessary. Instance variables consume memory while their
instance continues to exist, which makes them less efficient than local
variables, but potentially more efficient than Shared or Static variables.

Q> Develop a console application to demonstrate scope of variables in a module.
variableScope.vb


How to: Control the Scope of a Variable (Visual Basic or VB.net)

To make a variable visible only within a block
• Place the Dim Statement (Visual Basic) for the variable between the
initiating and terminating declaration statements of that block, for example
between the For and Next statements of a For loop.

To make a variable visible only within a procedure
• Place the Dim statement for the variable inside the procedure but outside
any block (such as a While...End While block).

To make a variable visible throughout a module, class, or structure
• Place the Dim statement for the variable inside the module, class, or
structure, but outside any procedure.
• Include the Private (Visual Basic) keyword in the Dim statement.
• You can refer to the variable from anywhere within the module, class, or
structure, but not from outside it.


To make a variable visible throughout a namespace
• Place the Dim statement for the variable inside the module, class, or
structure, but outside any procedure.
• Include the Friend (Visual Basic) or Public (Visual Basic) keyword in the Dim
statement.
• You can refer to the variable from anywhere within the namespace
containing the module, class, or structure.

Example: Declares a variable at module level and limits its visibility to code within the module.


Case study 1: The Investment Calculation Application
To be done by students as Home practicals
I/O of The Investment Calculator:

1 InvestCalc.exe
2 Initial Balance: 10000
3 Annual Interest (e.g. for 5%, enter 5): 5
4 Monthly Deposit: 200
5 Years of Investment: 30
6
7 If you start with $10,000.00,
8 and invest $200.00 per month
9 for 30 years
10 at 5% interest.
11 Your final balance would be: $211,129.17


Logic to be implemented
The program requires the user to enter the four values (Initial Balance,
Annual Interest, Monthly Deposit, and Years of Investment). In turn,
the program calculates the final balance. This calculation is known
as the Future Value (FV) calculation.

The formula( given in Question) for Future Value is
FV = MonthlyDeposit * (((1 + MonthlyInterest)^Months - 1 ) /
MonthlyInterest ) + StartingBalance * ( 1 + MonthlyInterest )^Months

FV = 200 * ( ( ( 1+5 /1200) ^ 360 – 1) / (5 / 1200) ) + 10000 * ( 1+
(5/1200) ) ^ 360

Refer awt pracs> ConsoleApplication2


Solution
• Create new project in Visual Basic .NET. Select
option “visual Basic Console Application”.
( Visual Basic .NET creates a new project with one module.)

2. Rename the file using the Solution Explorer. Right-click
on the filename Module1.vb in the Solution Explorer
and select Rename. Change the filename to
modInvest.vb.
3. Change the name of the Startup Object, also. Right-click
on the project in the Solution Explorer and select
Properties. On the General page, change the Startup
Object to Invest.


Controlling Flow in Programs
Visual basic.net consists of two categories of control statements:
1. Choice statements ( If , If-Else ,If-Elseif-Else, and select case)

2. Looping statements
• For..Next loop
• while..End While loop
• Do loop


Choice statements
The If statement

SYNTAX:
If <condition>Then
Code to execute if the condition is true
End If

Example program for If statement
Develop Application : Following are the grading rule of the mark list:
1) If the marks is greater than 80 then the student get higher first class
2) If the marks less than 80 and greater than 60 then the student get first class
3) If the marks less than 60 and greater than 40 then the student get second class
4) The last condition is , if the marks less than 40 then the student fail.

Refer loop demo > Windows Application 7 [change mark in the program]


Boolean Expressions and Boolean Logic
1. Comparison Operators:
– >, greater than
– <, less than
– =, equal to
– <>, not equal to
– >=, greater than or equal to
– <=, less than or equal to
– Like
Special characters that can be used with Like include
* to indicate any number of additional characters
? to represent one character
# to represent any digit (0–9)
Ranges ([a-g], for example) to specify that any character within that
range should be considered a match.


Example program using If statement and Like operator
(PatternMatcher.vb)
1 Public Class PatternMatcher
2 Shared Sub Main()
3 Dim sInput As String
4 Dim sPattern As String
5 Dim sMatch As String
6
7 System.Console.Write(“Please Enter A Pattern:”)
8 sInput = System.Console.ReadLine()
9 sPattern = sInput
10
11 System.Console.Write(“Please Enter A String To Compare
Against:”)
13 sMatch = sInput
14


15 If sMatch Like sPattern Then
16 System.Console.WriteLine(sMatch & “ Matched with “ & sPattern)
17 Else
18 System.Console.WriteLine(sMatch & “ did not Match with “ & sPattern)
19 End If
20 End Sub
7 End Class


Loops :

Whenever you face a situation in programming to repeat a task for
several times (more than one times ) or you have to repeat a task till
you reach a condtition, in these situations you can use loop statements
to achieve your desired results.
• FOR NEXT Loop, FOR EACH Loop , WHILE Loop and DO WHILE Loop are the
Commonly used loops in Visual Basic.NET 2010 .

FOR NEXT Loop :
• The FOR NEXT Loop , execute the loop body (the source code within For ..Next code
block) to a fixed number of times.

• For var=[startValue] To [endValue] [Step] [loopBody] Next [var]
var : The counter for the loop to repeat the steps.
starValue : The starting value assign to counter variable .
endValue : When the counter variable reach end value the Loop will stop .
loopBody : The source code between loop body.


Show a messagebox 5 times and each time you want to see how many times
the message box shows. Logic : refer loop demo > windows application3

1. startVal=1
2. endVal = 5
3. For var = startVal To endVal
4. show message
5. Next var


If you want to Exit from FOR NEXT Loop even before completing the loop
Visual Basic.NET provides a keyword Exit to use within the loop body.

Refer loop demo > Windows Application 4

Nested For loop
Create a 2 dimensional array using 2 for loops.

While ..End While
Syntax :
While [condition]
[loop body]
End While


Logical Operators:
Binary : AND, OR, and XOR

Unary :NOT

Viva : What is Short Circuiting Concept?

To make Visual Basic .NET short-circuit a Boolean expression, we
need to use alternative forms of the AND and OR operators,
ANDALSO and ORELSE.


Example program to test ANDALSO:
ShortCircuiting.vb
1 Public Class ShortCircuiting
2
3 Shared Sub Main()
4 If Test(“Left”) ANDALSO Test(“Right”) Then
5 ‘do something
6 End If
7 End Sub
8
9 Shared Function Test(sInput As String) As Boolean
10 System.Console.WriteLine(sInput)
11 Test = FALSE
12 End Function
13
14 End Class


WhileSearch.vb
1 Imports System Demonstrate use of AND operator
2 Public Class WhileExample
4 Shared Sub Main()
4 Dim iCounter As Integer = 0
5 Dim arrList(10) As String
6 Dim iMatch As Integer = -1
7 Dim sMatch As String
8 sMatch = “Chembur”
9 arrList(0) = “thane”
10 arrList(1) = “Chembur”
11 arrList(2) = “Ghatkopar”
12 arrList(3) = “dadar”
13 arrList(4) = “Borivali”
14 arrList(5) = “andheri”
15 arrList(6) = “Nerul”
16 arrList(7) = “Panvel”
17 arrList(8) = “Belapur”
18 arrList(9) = “Worli”
19 While iCounter <= 9 AND iMatch = -1

65

20 If arrList(iCounter) Like sMatch Then
21 iMatch = iCounter
22 Else
23 iCounter = iCounter + 1
24 End If
6 End While
26 If iMatch <> -1 Then
27 System.Console.WriteLine(“Matched “ & iMatch)
28 End If
29 End Sub
31 End Class


Do Loop:
SYNTAX:
Do
Code to be executed
Loop

The syntax doesn’t specify any exit condition so the code will continue to
execute forever.

There are 2 forms :
Do While iMatch = 3 // note : Truewala
// Code to be executed
Loop

Do Until Not (iMatch = 3) // note : Falsewala
‘iMatch <> 3 would have also worked
Loop


Q> Write a Program to read from a file using Do…Loop and .Net
Framework classes.

NOTE:
Use two different objects, both part of the System.IO namespace of the .Net
Framework, System.IO.File and System.IO.StreamReader.

System.IO.File has methods like open(), openText() , openRead() , openwrite()

System.IO.StreamReader : has methods like read() and readLine()


1 Public Class ReadFromFile
2
3 Shared Sub Main()
4 Dim sFileName As String
5 Dim srFileReader As System.IO.StreamReader
6 Dim sInputLine As String
7
8 sFileName = “MySampleFile.txt”
9 srFileReader = System.IO.File.OpenText(sFileName)
10 sInputLine = srFileReader.ReadLine()
11 Do Until sInputLine is Nothing
12 System.Console.WriteLine(sInputLine)
13 sInputLine = srFileReader.ReadLine()
14 Loop
15 End Sub
16 End Class

Note : To run this code create a text file with sample content in the same
directory as the compiled executable. [ file class in detail in module 3 ]


Define Recursion with an example. (RecursiveFactorial.vb )

1 Public Class RecursiveFactorial
2 Shared Sub Main()
3 Dim sInput As String
4 Dim iInput As Integer
5 Dim iCounter As Integer
6 Dim iFactorial As Integer
7 System.Console.Write(“Please Enter A Number: “)
9 iInput = CInt(sInput)
10 System.Console.WriteLine(Factorial(iInput))
11 End Sub
12
13 Shared Function Factorial(n as Integer) as Integer
14
15 If n = 1 Then
16 Return 1
17 Else
18 Return n * Factorial(n-1)
19 End If
20 End Function
21 End Class


Module 3: Streams And Files

Stream : It is a flow of information that passes in some sequential manner.


Methods of the File Class
Methods Description
Copy Copies a file.
Create Creates a new file.
CreateText A special version of Create that creates a text file.

Delete Deletes a file.
Exists Returns True if the file exists.

Open Opens a file for reading, writing, or both.

OpenRead Specialized version of Open that always opens the file for reading.
Specialized version of Open that opens text files only for reading.

OpenText This would be a handy shortcut if you were writing an application
that needed to read configuration information, or a log file.

OpenWrite Specialized version of Open that always opens the file for writing.


Methods and Properties of FileStream.
Viva : why use Filestream class over File class?
Filestream class is having more defined methods for reading, writing.
Name Description

// Property

Length Number of bytes in the file.
Position The current position in the file.

Close ( ) Closes the FileStream.
Read ( ) Reads a number of bytes from the FileStream. The return value is an
array.
Seek ( ) Moves forward or backward through the file.

Write ( ) Writes a number of bytes to the FileStream.


Viva Q : We always read from StreamReader
which reads with FileStream
The Read method of the FileStream class deals with bytes.

If you apply a StreamReader to the FileStream we can read
information in the file as Chars or ints or whatever form they are.


Important Methods of the StreamReader
Name Description

Close Closes the StreamReader.

Read Reads the next character from the Stream. (one character at a time.)

ReadBlock Reads a block of characters from the Stream.

ReadLine Reads the next line from the Stream. Viva : used wrt Files

ReadToEnd Reads all the characters from the Stream at once.
This is the fastest way to get all the information out of the Stream and into
a variable.


Eg 1: Reading from a File . List steps for creating a file.
A> 1st create obj of FileStream, 2nd create obj StreamReader
1 Dim oFile As FileStream
2 Dim oReader As StreamReader
3 Dim sContents As String

5 oFile = New FileStream(“MyFile.txt”, FileMode.OpenOrCreate,
FileAccess.Read)

7 oReader = New StreamReader(oFile)

9 sContents = oReader.ReadToEnd()

7 oReader.Close()
8 oReader = Nothing
9 oFile = Nothing

Writing to a Text File using
StreamWriter
Name Description
Close Closes the StreamWriter.

Write Writes to the Stream.

WriteLine Writes to the Stream, ending the added information with a new
line.


Eg 2: Writing to a File
1 Dim oFile As FileStream
2 Dim oWriter As StreamWriter
3 oFile = New FileStream(“MyFile.txt”, _
4 FileMode.OpenOrCreate, FileAccess.Write)
5 oWriter = New StreamWriter(oFile)
6 ’Writes the Integer 123 to the file
7 oWriter.Write(123)
8 ’Writes the String “Customer” to the file
9 oWriter.Write(“Customer”)
10 ’Writes the String “Suven Consultants” to the file, next writes will be on a
new line
11 oWriter.WriteLine(“Suven Consultants”) //Writes on the new line
12 oWriter.Close()
13 oWriter = Nothing
14 oFile = Nothing


Example: Create a temporary file and writes some text to it. Then open the file,
using System.IO.FileMode.Open; that is, if the file did not already exist, it
would not be created.

1> The declaration of the Open is
Public Shared Function Open (path As String, mode As FileMode ) As FileStream

refer awt pracs > file demo.


Module 4 : EXCEPTION HANDLING

Syntax for Try…End Try ( or syntax for exception handling )

Q. Write a program with intentional exception, so you can see how it works and
do exception handling.
Ans >

1 Module modExceptional
2 Sub Main()

3 Dim dDividend As Decimal = 5
4 Dim dDivisor As Decimal = 0
6 Dim dResult As Decimal = 0

8 dResult = dDividend / dDivisor

7 System.Console.ReadLine()
8 End Sub
9
10 End Module


The o/p of the above program through IDE


The o/p of the above program through command prompt

1 Unhandled Exception: System.DivideByZeroException:
2 An exception of type System.DivideByZeroException was thrown.
3 System.Decimal.Divide(Decimal d1, Decimal d2)
4 at Exceptions.modExceptional.Main() in
5 modExceptional.vb:line 6

Note : Moment the program runs , as it contains an exception , the line
at which an exception occurs Just-In-Time Debugging dialog
opens. Select No. then we see the above o/p.


Exception handling in the Above program
1 Module modExceptional
2 Sub Main()
3 Dim dDividend As Decimal = 5
4 Dim dDivisor As Decimal = 0
5 Dim dResult As Decimal = 0
6 Try
7 dResult = dDividend / dDivisor
8 Catch Ex As Exception
9 System.Console.WriteLine(“A division by zero error has occurred.”)
10 System.Console.WriteLine(“Please check the divisor.”)
11 End Try
12 System.Console.ReadLine()
13 End Sub
14 End Module


Q. Can try-blocks be nested. Demonstrate with program
which writes days current time and date to a file.( 4m )
1 Sub WriteToFile(ByVal FileName As String)
2 Dim fsOut As System.IO.FileStream
3 Dim strOut As System.IO.StreamWriter
4 Try
5 ‘Open the File Open, OpenCreate,
6 fsOut = _ OpenRead,OpenWrite
7 New System.IO.FileStream(FileName, _
8 System.IO.FileMode.OpenOrCreate, _
9 System.IO.FileAccess.Write)
10 Try
11 ‘Write to the file
12 strOut = _ Today , now attributes

13 New System.IO.StreamWriter(fsOut)
14 strOut.Write(DateTime.Today.ToString())
15 Catch eIO As Exception

16 Console.WriteLine(“Couldn’t write to file: {0}.”, FileName)
17 End Try
18 Catch eFile As Exception
19 Console.WriteLine(“Couldn’t open file: {0}.”, FileName)
20 End Try
21 End Sub


Raising Exceptions by using “Throw” keyword
The Throw Statement
1 Dim oCust As Customer = New Customer(“abc”, “xyz”)
3 Dim oEmp As Employee = New Employee(“abc1”, “xyz1”)
// assumption …

3 Dim oSomething As Object
4 oSomething = oEmp
5 If TypeOf oSomething Is Customer Then
6 oCust = oSomething
7 Else
8 Throw New InvalidCastException(“Cannot assign an Employee to a Customer.”)
9 End If

O/p: Opens dialog box (by the default debugger) with the message above.


List all the exceptions that might occur when calling the File.Open method. Or
All exceptions related to file operations

To test this procedure, try a number of specific exceptions. For example, change the file
name to be:

In a valid path, but select a file that doesn't exist.
On a drive that doesn't exist.
In a path that doesn't exist.
On a drive that isn't ready.


If no file name given

If wrong file name given

If Nothing entered

Self
explanatory


List all exceptions under the ArgumentException class.

ArgumentException is thrown when a method is invoked and at least one of the passed
arguments does not meet the parameter specification of the called method.

ArgumentNullException whenever a null reference (Nothing in Visual Basic) is
passed to a method that does not accept it as a valid argument.

ArgumentOutOfRangeException when the value of an argument is outside the
range of acceptable values; for example, when the value "46" is passed as the month
argument during the creation of a DateTime.

InvalidEnumArgumentException thrown when using invalid arguments that are
enumerators.


92

Home assignment

2. Specify with e.g.. ( not complete code ) use of following exceptions

• ArgumentNullException
• ArgumentOutOfRangeException
• IndexOutOfRangeException
• OverflowException
• FileNotFoundException


An IndexOutOfRangeException exception is thrown when an attempt is made
to access an element of an array or collection with an index that is outside the
bounds of the array or less than zero.

• Make sure that the maximum index on a list is less than the list size
• Make sure the index is not a negative number.
• Make sure data column names are correct.

Example :
Uses a Try…Catch block to trap the IndexOutOfRangeException when
index i is outside the array bounds, 0 to 3.

The example displays the following:
• Element at index 0: 3
• Element at index 2: 5
• Element at index -1: IndexOutOfRangeException caught
• Element at index 4: IndexOutOfRangeException caught


The exception that is thrown when an arithmetic, casting, or conversion
operation in a checked context results in an overflow.


Module 5 : OO Programming Concepts


Creating Classes:
Step 1 > Open up Visual Studio .NET, and
create a new Empty Project from under
the Visual Basic Projects folder.

Step 2 > Add Class from the project menu.
This adds a new, empty class to the
project.

Step 3> The above class is empty ,
therefore put Properties into it.
In Vb.NET property is a special method
which is designed to assign and read
values of class data. Each property has
2 methods get( ) and set( ). Get is used
for retr values and set used for initzn it.

98

Eg . Of Set and Get methods

Understand a class definition , using constructor.
Refer exp 4> module 4.vb – this console application does not use get() and set()

Understand class definition with get() and set() , interface definition.
Refer exp 5> module 4.vb


Why to create Properties.

• To create a property within a class, you can either create a field (i.e.. a
Public variable), or you can create a Private variable and expose the Private
variable using a Property statement.

There are several reasons to expose properties through a Property statement.
• You can create a read-only or write-only property, as opposed to a Public
variable, which will always be read-write.
• You can add error handling within a Property statement to check for invalid
values being set. You can't check for invalid values when setting a Public
variable because there is no code that runs in response to setting a Public
variable.
• You can expose calculated values as properties even if they are not stored
as actual data within the class.

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Properties can be
1> ReadOnly
2> WriteOnly

For a write-only property
Dim m_sPassword As String
Public WriteOnly Property Password() // no rtype as no get method
Set(ByVal Value As String)
m_sPassword = Value
End Set

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Develop the sub main () to instantiate an object of class Line .

output :

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Overloading : By using Overloads keyword ahead of the Function or Sub

Definition:

Use:

Refer exp 5 > module3.vb

How would we call these methods with different set of parameters.
>

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Inheritance : Child class deriving properties from a parent, using keyword inherits
Understand single Inheritance

Understand multi level Inheritance
Refer exp 5 > solved.vb

Understand multiple Inheritance ( same as java using Class and Interface)

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Over riding
• Derived classes inherit properties and methods defined in their base class. This
is useful because it means you can reuse these items when appropriate for the
class you are using. If the inherited member cannot be used "as is" you have the
option of using the Overrides keyword to define a new implementation, provided
that the property or method in the base class is marked with the Overridable
keyword, or shadowing the member by redefining it in the derived class.
• Overridden members are used to implement polymorphism.

The following rules apply to overriding methods.
• You can only override members that are marked with the Overridable keyword
in their base class.
• Properties and methods are NotOverridable by default.
• Overridden members must have the same arguments as the inherited members
from the base class.
• The new implementation of a member can call the original implementation in the
parent class by specifying MyBase before the method name.

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Q> what is the use of the k/w “Overridable ”.
For a child class to override some part of the base class, that portion must
be marked Overridable in the base class definition.

1 Public Class Vehicle
2
3 ‘Code removed for simplicity....
4
5 Public Overridable Function Description() As String
6 Return “This is my generic vehicle description!”
7 End Function
8 End Class
9
10 Public Class Car
11 Inherits Vehicle
12
13 ‘Code removed for simplicity....
14
15 Public Overrides Function Description() As String
16 Return “This is my Car Description”
17 End Function
18
19 End Class
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Example defines a base
class, Payroll, and a derived
class, BonusPayroll, which
overrides an inherited
method, PayEmployee.

A procedure, RunPayroll,
creates and then passes a
Payroll object and a
BonusPayroll object to a
function, Pay, that executes
the PayEmployee method of
both objects.

107

Constructors
Constructors and destructors control the creation and destruction of objects.
• To create a constructor for a class, create a procedure named Sub New
anywhere in the class definition. To create a parameterized constructor,
specify the names and data types of arguments to Sub New.

Eg : Sub New(ByVal sString As String)

Constructors can be overloaded, as in the following code:
Sub New(ByVal sString As String, iInt As Integer)

• When you define a class derived from another class, the first line of a
constructor must be a call to the constructor of the base class, unless the
base class has an accessible constructor that takes no parameters. A call to
the base class containing the above constructor, for example, would be
MyBase.New(sString). Otherwise, MyBase.New is optional, and the Visual
Basic .NET runtime calls it implicitly.

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Q> How to define a constructor? (4m)
Ans: The creation of a constructor for Vehicle class
Step 1: create a method named New that is public and has no parameters.
Public Sub New()
End Sub

Step 2: Initialize internal
variables of the class.

Step 3: to call the Base
class constructor fro m
The child class

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• Finalize Methods and Destructors
• For the majority of the objects that an application creates, the .NET
Framework's garbage collector implicitly perform all the necessary memory
management tasks.

• However, when you create objects that encapsulate unmanaged resources,
you must explicitly release the unmanaged resources when you are finished
using them in your application. The most common type of unmanaged
resource is an object that wraps an operating system resource, such as a
file, window, or network connection. Although the garbage collector is able
to track the lifetime of an object that encapsulates an unmanaged resource,
it does not have specific knowledge about how to clean up the resource. For
these types of objects, the .NET Framework provides the
Object.Finalize method, which allows an object to clean up its unmanaged
resources properly when the garbage collector reclaims the memory used
by the object.

Implementing Finalize methods or destructors can have a negative impact
on performance and you should avoid using them unnecessarily.

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Module 6 : Namespaces (similar to concept of Packages in Java)

Viva : Q : why is it needed.
Namespaces organize the objects defined in an assembly. Assemblies can
contain multiple namespaces, which can in turn contain other namespaces.
Namespaces prevent ambiguity and simplify references when using large
groups of objects such as class libraries. Example of Name Spaces :

Within a namespace, you can define items such as modules, interfaces,
classes, delegates, enumerations, structures, and other namespaces. You
cannot define items such as properties, procedures, variables and events at
the namespace level. These items must be declared within containers such as
modules, structures, or classes.

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When should we use global Keyword.

If you have defined a nested hierarchy of namespaces, code inside that
hierarchy might be blocked from accessing the System namespace of the .NET
Framework. The following example illustrates a hierarchy in which the
SpecialSpace.System namespace blocks access to System.

As a result, the Visual Basic compiler cannot successfully resolve the reference
to System.Int32, because SpecialSpace.System does not define Int32. You can
use the Global keyword to start the qualification chain at the outermost level of
the .NET Framework class library. This allows you to specify the System
namespace or any other namespace in the class library. The following example
illustrates this. 112

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• Console: Enables reading and writing to the command-line.

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Eg: Using the Console Class for Input and Output .
1 Imports System
2 Public Class ConsoleTest
3 Private Const ITEM_COUNT As Integer = 10
4 Shared Sub Main()
5 Dim I As Integer
6 Dim sItems(ITEM_COUNT) As String
7 Console.WriteLine(“Please enter {0} items. “ & _
8 Press ENTER between items.”, ITEM_COUNT)
8 For I = 0 To ITEM_COUNT-1
9 sItems(I) = Console.ReadLine
10 Next
11 Console.WriteLine()
12 Console.WriteLine(“Items in reverse order:”)
14 For I = ITEM_COUNT - 1 To 0 Step -1
14 Console.WriteLine(sItems(I))
15 Next
16 End Sub
17 End Class
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Redirection: sending the o/p and error messages or recv the i/p
from a device or place other than the default

Dg :

1 Imports System
2 Imports System.IO
3 Public Class ConsoleTest
4 Private Const ITEM_COUNT As Integer = 10
5 Shared Sub Main()
13 Dim I As Integer

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6 Dim I As Integer
7 Dim sItems(ITEM_COUNT) As String
8 Dim oFile As TextWriter = File.CreateText(“Output.txt”)
9 Dim oOut As TextWriter = Console.Out //Needed to reset the
output back from file
to monitor.
10 Console.WriteLine(“Please enter {0} items. Press ENTER between
items.”, ITEM_COUNT)
11 For I = 0 To ITEM_COUNT-1
12 sItems(I) = Console.ReadLine
13 Next
14 Console.WriteLine()
15 Console.SetOut(oFile)
16 Console.WriteLine(“Items in reverse order:”)
17 For I = ITEM_COUNT - 1 To 0 Step -1
18 Console.WriteLine(sItems(I))
19 Next
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Running the application:

1 [c:workconsole]Console2.exe
2 Please enter 10 items. Press ENTER between items.
3 Aardvark
4 Bandicoot
5 Cassowary
6 Dugong
7 Echidna
8 Finch
9 Giraffe
10 Hippopotamus
11 Iguana
12 Jackalope
13
14 Done

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The code should produce a file Output.txt with the following contents:

1 Items in reverse order:
2 Jackalope
3 Iguana
4 Hippopotamus
5 Giraffe
6 Finch
7 Echidna
8 Dugong
9 Cassowary
10 Bandicoot
11 Aardvark

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2. Environment class
Provides information about, and means to manipulate, the current environment and
platform. This class cannot be inherited.

Refer awt pracs >console application 4

120

121

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Use the Environment class to retrieve information such as command-line
arguments, the exit code, environment variable settings, contents of the call
stack, time since last system boot, and the version of the common language
runtime.

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Methods and Properties of the Environment Class

125

3. Random :
Represents a pseudo-random number generator, a device that produces a
sequence of numbers that meet certain statistical requirements for randomness.

Constructors :

Methods

126

Eg . Random class
Dim oRand As New Random
Dim iValue As Integer = oRand.Next(1, 100)

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4. Collection Classes in the .NET Framework
The .NET Framework provides specialized classes for data storage and
retrieval. These classes provide support for stacks, queues, lists, and hash
tables.

4. A . ArrayList : Is a Array which can hold objects .
Intially it is empty and has the default initial capacity. The size can dynamically
change.

Dim arrList As New ArrayList
‘creates a new ArrayList, with 16 members initially

Dim arrList2 As New ArrayList(20)
‘ creates a new ArrayList, with 20 members initially

Methods : add(int n ), retrieve(int n), and delete(int n)

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4.b) Queue : A Queue is a “first-in, first-out” (FIFO) collection

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Queues are useful for storing messages in the order they were received for
sequential processing. This class implements a queue as a circular array. Objects
stored in a Queue are inserted at one end and removed from the other.

The capacity of a Queue is the number of elements the Queue can hold. As
elements are added to a Queue, the capacity is automatically increased as
required through reallocation. The capacity can be decreased by calling
TrimToSize.

The growth factor is the number by which the current capacity is multiplied when a
greater capacity is required. The growth factor is determined when the Queue is
constructed. The default growth factor is 2.0. The capacity of the Queue will
always increase by at least a minimum of four, regardless of the growth factor.

For example, a Queue with a growth factor of 1.0 will always increase in capacity
by four when a greater capacity is required.

Queue accepts Nothing as a valid value and allows duplicate elements.

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4.c) Stack: Is a “first-in, last-out” (FILO) or LIFO collection

135

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4.d SortedList: Represents a collection of key/value pairs that are sorted by
the keys and are accessible by key and by index.

A SortedList object internally maintains two arrays to store the elements of the
list; that is, one array for the keys and another array for the associated values.
Each element is a key/value pair that can be accessed as a DictionaryEntry
object. A key cannot be Nothing, but a value can be.

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Module 7: Accessing Data with .Net

ADO.Net:
ADO.NET is the data access technology that is part of
the .NET Framework
• In .NET, database access is handled by the classes in
and under the System.Data namespace.
• The namespace is divided into two distinct areas: the
System.Data.OleDB classes and the
System.Data.SQLClient classes. The first set,
System.Data.OleDB, is designed to allow you to connect
to any database for which we have an OLEDB provider
i.e an ODBC driver.
• System.Data.SQLClient, is designed to work only with
Microsoft SQL Server,
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Standard Database Tasks( # )
1> Connecting to Database:
Requires 2 elements the connection object and a connection string.
// in java we have simply make a connection object by providing a data source name.
• In ADO.NET, there are two different connection objects
(one for OLEDB and one for SQL Server). Before you can
start coding, you should obtain the proper connection
string for your database. Which can be obtained by
opening special file of Microsoft Datalink.
• Follow these steps to create a Microsoft Datalink file (.udl )
and retrieve from it connection string information:

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• Create a blank Microsoft Data Link file by creating a new text file
and renaming it to something with a .udl file extension (New.udl)

• Double-click the new file, and a dialog appears with a set of four
tabs for creating and editing the connection information for your
database.

• Using the dialog that has just opened, start with the first tab,
Provider, and set up the correct information for your database:
– For the Access database select the Microsoft Jet 4.0 provider.
– For SQL Server database, select the Microsoft OLEDB
Provider for SQL Server.

Now the second tab “ Connection tab “, select the path For Access
(.mdb file.) // this depends on provider.

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• Test the connection (by Clicking the Test Connection button )
• If the test successful then close datalink properties window
• open the .udl file

It contains the following connection string for access database
[oledb]
; Everything after this line is an OLE DB initstring
Provider=Microsoft.Jet.OLEDB.4.0;Data Source=student;Persist Security Info=False

The contents of a .udl file configured for SQL Server is
[oledb]
; Everything after this line is an OLE DB initstring
Provider=SQLOLEDB.1;Password=password;
Persist Security Info=True;User ID=sa;
Initial Catalog=CD;Data Source=(local)

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• To create a connection, you need to create a new instance of either the
System.Data.OleDB.OLEDBConnection
or the
System.Data.SqlClient.SQLConnection
A connection string to make connection with .mdb
1 Module Module1
2 Private Const sConnection As String =”Provider=Microsoft.Jet.OLEDB.4.0;” &_
8 “Data Source=C:CD.mdb;”&_
4 “Persist Security Info=False”
5
6
7 Sub Main()
8 Dim objConn As New System.Data.OleDb.OleDbConnection(sConnection)
9 End Sub
10 End Module

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2> Opening Connection
1 Module Module1
2 Private Const sConnection As String = “Provider=
Microsoft.Jet.OLEDB.4.0;” & _
3 “Data Source=C:CD.mdb;”&_
4 “Persist Security Info=False”
5 Sub Main()
6 Dim objConn As New
System.Data.OleDb.OleDbConnection(sConnection)
7 Try
8 objConn.Open()
9 Catch myException As System.Exception
10 Console.WriteLine(myException.Message)
11 End Try
12 Console.ReadLine()
13 End Sub
14 End Module

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For Opening a connection with the SQLServer

Use SQLClient class

Modify the above program :

First: Remove the Provider section from your connection
string and

second : Change your objConn declaration to refer to the
System.Data.SQLClient.SQLConnection object
instead of the OLEDB class.

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Opening connection with SQL server #
1 Imports System
2 Module Module1
3 Private Const sConnection As String
4 sConnection = “Password=password;” & _
5 “Persist Security Info=True;” & _
6 “User ID=sa;” & _
7 “Initial Catalog=CD;” & _
8 “Data Source=(local)”
9 Sub Main()
10 Dim objConn As New Data.SqlClient.SqlConnection(sConnection)
11 Try
12 objConn.Open()
13 Catch myException As Exception
14 Console.WriteLine(myException.Message)
15 End Try
16 Console.ReadLine()
17 End Sub
18 End Module

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3. Executing a SQL Statement
After a connection is established we can add, delete, modify, and retrieve
records. To accomplish any of those tasks, you can use a command object
(SQLCommand or OleDBCommand) to represent and then execute a
SQLstatement.

Steps are:
a) Create a connection object using the connection string.

b) Create a command object of OLEDB command or SQL command.

c) Open connection with database. Refer exp6 > Application1

d) Create object of OleDbDataAdapter.

e) Use fill().
This executes the query. DataSet can hold one or more table objects.

f) Use DataGrid.
Dataset cannot show the records of the table, use Datagrid
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Data Set (System.Data.DataSet).
.NET provides a totally disconnected model of data access through
the Data Set (System.Data.DataSet). Data Sets are capable of
loading information, from a database and then disconnecting.

Here the data becomes independent of its original source. This
independence from the data source is why this information is
considered disconnected and can be kept for as long as needed in a
totally offline environment.

Note: If u make changes to the dataSet does it affect the data source.
Ans >

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1. Getting Data into a Data Set :
# To load data from the database into a DataSet, we will need a data
adapter. The data adapter objects, SQLDataAdapter and
OleDBDataAdapter, are designed to provide the glue or link between
your database and a DataSet object. This link works in two parts,
filling the DataSet, and then sending changes on the DataSet back
to the data source to update the original data.

Steps : 1> Create a connection object.
2> Create the appropriate data adapter class (OLEDB or SQL)
3> Use the desired SQL statement, or a command object that
refers to the correct SQL, and the connection object in the
constructor of the data adapter, and it will be completely set up
i.e. Data Adapter object is installed.

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4.To fill the dataset with the results of query, a DataSet object must first
be created.
Dim objDS As New DataSet(“dummy_dataSet”)

5. To load the data into the DataSet, use the Fill method of the
DataAdapter, but before that will work, the connection object must
be opened successfully:
objConn.Open()
objDataAdapter.Fill(objDS, “Disc”)

After the above code has executed, a table has been created inside
the DataSet, with the name “Disc”, and filled with the results of your
SQL query.

6. To work with its contents through the DataSet’s Tables collection:
Console.WriteLine(“{0} Rows”, objDS.Tables(“Disc”).Rows.Count)

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Viva : dataset is a disconnected model . Justify.

As the DataSet is a disconnected object, you could have completely
closed the connection to your database before working with the
DataSet’s contents; therefore,

objConn.Close()
Console.WriteLine(“{0} Rows”, objDS.Tables(“Disc”).Rows.Count)

o/p :

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2. Navigation Data
1> After populating the Data Set, we have to retrieve 1 table out of the data
Set.
( Note : why?
Because Dataset is a collection of tables.)

Dim objTable As DataTable
objTable = objDS.Tables(“Disc”)

The DataTable object provides two collections :
1> The Rows collection, which contains all the records from the table,
and the Columns collection, which contains a collection of
DataColumn objects describing each individual field in the table.
The Rows collection can be used in one of several ways to loop
through all the records of the table:

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Eg 1: Using a For Each loop

Dim objRow As DataRow
For Each objRow In objTable.Rows
Console.WriteLine(objRow.Item(“CDTitle”)) // Item() retrieves attr value
Next // it takes index value or attr name

Eg 2: Using a regular For loop

Dim i As Integer
For i = 0 To objTable.Rows.Count - 1
objRow = objTable.Rows(i)
Console.WriteLine(objRow.Item(“CDTitle”))

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The Columns collection contains details of the fields of the DataTable, each
one represented as a DataColumn object. We can loop through the table’s
fields using either a For Each or a For loop:

Dim objColumn As DataColumn
For Each objColumn In objTable.Columns
Console.WriteLine(“Column Name: {0} Data Type: {1}”, _
objColumn.ColumnName, _
objColumn.DataType.FullName)
Next

Develop an application - creating a table dynamically in the program and
showing it in the DataGrid. Do not connect to any Database.

Refer Exp6 > application2

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Home Assignment

Develop an application having UI to navigate through the database.
Connect to the Student table having at least 2 columns – Roll no. , name.

Use DataView and CurrencyManager object.

Refer Exp6> application3

Develop an application to generate an XML file representing the table. The
table ( DataTable object ) is created by adding some Columns.
To generate XML ( tags showing the schema of the table) , use GetXml()
method over the DataSet object.

Refer Exp7>consolbased

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Develop an application – creating
table and writing its schema to an
xml file. Use WriteXML ( String,
WriteXMLMode )

Refer exp 7 > empdetial

Another Example :

Refer exp 7 > solved
// this program contains Contact information

Refer exp 7 > studentinfo
// this program contains student information

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3> Editing Data (Add, Edit, Delete) using DataSet object
When we modify the database through the DataSet the changes are not
committed. The changes you make to the DataSet will be translated by the
DataAdapter into the SQL statements that need to be executed against the
database.

DataAdapter.Update Method
Calls the respective INSERT, UPDATE, or DELETE statements for each
inserted, updated, or deleted row in the specified DataSet from a DataTable
named "Table."
Namespace: System.Data.Common

The update is performed on a by-row basis. For every inserted, modified,
and deleted row, the Update method determines the type of change that has
been performed on it (Insert, Update or Delete). Depending on the type of
change, the Insert, Update, or Delete command template executes to
propagate the modified row to the data source. When an application calls
the Update method, the DataAdapter examines the RowState property, and
executes the required INSERT, UPDATE, or DELETE statements iteratively
for each row, based on the order of the indexes configured in the DataSet.

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For example, Update might execute a DELETE statement, followed by an
INSERT statement, and then another DELETE statement, due to the ordering of
the rows in the DataTable.

If INSERT, UPDATE, or DELETE statements have not been specified, the
Update method generates an exception. However, you can create a
SqlCommandBuilder or OleDbCommandBuilder object to automatically generate
SQL statements for single-table updates if you set the SelectCommand property
of a .NET Framework data provider. Then, any additional SQL statements that
you do not set are generated by the CommandBuilder.

Working of the Update method:
• The Update method retrieves rows from the table listed in the first mapping
before performing an update. The Update then refreshes the row using the value
of the UpdatedRowSource property. Any additional rows returned are ignored.

• After any data is loaded back into the DataSet, the OnRowUpdated event is
raised, allowing the user to inspect the reconciled DataSet row and any output
parameters returned by the command. After a row updates successfully, the
changes to that row are accepted.

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When using Update, the order of execution is as follows:

• The values in the DataRow are moved to the parameter values.
• The OnRowUpdating event is raised.
• The command executes.
• If the command is set to FirstReturnedRecord, then the first returned result is
placed in the DataRow.
• If there are output parameters, they are placed in the DataRow.
• The OnRowUpdated event is raised.
• AcceptChanges is called.

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Adapter has many properties

To create the SQL query

To check for any update

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• SelectCommand
Note : properties of adapter object. • InsertCommand
• UpdateCommand
• DeleteCommand

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161

Refer

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Short note on OleDbCommandBuilder
• The OleDbDataAdapter does not automatically generate the SQL statements required to
reconcile changes made to a DataSet with the associated data source.
• OleDbCommandBuilder object is needed to automatically generate SQL statements for
single-table updates if you set the SelectCommand property of the OleDbDataAdapter.

• The OleDbCommandBuilder registers itself as a listener for RowUpdating events
whenever you set the DataAdapter property. You can only associate one
OleDbDataAdapter or OleDbCommandBuilder object with each other at one time.

• To generate INSERT, UPDATE, or DELETE statements, the OleDbCommandBuilder
uses the SelectCommand property to retrieve a required set of metadata automatically.

• The OleDbCommandBuilder also uses the Connection, CommandTimeout, and
Transaction properties referenced by the SelectCommand. The user should call
RefreshSchema if one or more of these properties are modified, or if the SelectCommand
itself is replaced. Otherwise the InsertCommand, UpdateCommand, and DeleteCommand
properties retain their previous values.

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1. Adding Records
After you have created a connection, created a data adapter, and
loaded some data into your DataSet, you can directly access a
DataTable object:

After you have that DataTable, you can access its contents through the
Rows collection, which returns a DataRowCollection object.
Dim drRows As DataRowCollection
drRows = objTable.Rows

This object represents all the records in the table as a collection of
DataRow objects. The collection itself provides a method, Add, to create
new records.

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Adding a DataRow to a Data Table by passing of a DataRow Object
as the Parameter to the Add Method of DataRow collection.

1 Dim drRows As DataRowCollection //Contains all Rows
2 Dim objNewRow As DataRow
3 drRows = objTable.Rows //Returns all Rows
4
5 ‘Assume - we have 3 columns
6 ‘ArtistID
7 ‘ArtistName
8 ‘CDTitle
9
10 objNewRow = objTable.NewRow() //Instantiating a new Row
object with schema/structure of the
ObjTable.
11 objNewRow(“ArtistID”) = 3
12 objNewRow(“ArtistName”) = “Mohit Chawan”

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13 objNewRow(“CDTitle”) = “NewYork”
2 drRows.Add(objNewRow) //Adding new Row to the DataTable

Note : These changes are reflected to the Database Server only after the update( ).

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Steps similar to adding records.

2. Editing Records:
objRow = drRows(5) ‘ retriving the 5th row
Each individual DataRow object has several methods for editing:
BeginEdit, EndEdit, and CancelEdit. BeginEdit and EndEdit put the
DataRow into and out of edit mode, which is a special state in which the row
maintains information about the in-progress edit, and therefore change
events will not fire for each individual field modification.

For Eg:
objRow.BeginEdit()
objRow(“student_name”) = “Suven”
objRow.EndEdit()

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3. Deleting Records:
objRow = drRows(3) // Retreiving 3rd row
objRow.delete() // or drRows.Remove(3)

Note : Remove() used when changes are not to be
committed to the database. Therefore used delete().

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Demonstrate use of adapter.DeleteCommand and ExecuteNonQuery()
Imports System.Data.SqlClient
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Dim connetionString As String
Dim connection As SqlConnection
Dim adapter As New SqlDataAdapter
Dim sql As String connetionString = "Data Source=ServerName;Initial
Catalog=DatabaseName;User ID=UserName;Password=Password"
connection = New SqlConnection(connetionString)
sql = "delete product where Product_name ='Product7'"
Try
Refer awt pracs>DB Navigation
connection.Open()
adapter.DeleteCommand = connection.CreateCommand
adapter.DeleteCommand.CommandText = sql
adapter.DeleteCommand.ExecuteNonQuery()
MsgBox("Row(s) deleted !! ")
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
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End Class

Module 8: Multi threading - Concept and Program

Multithreading is new to VB .NET. The .NET Framework, and thus VB.NET
provides full support for multiple execution threads in a program. You can
add threading functionality to your application by using the
System.Threading namespace.

– A thread in .NET is represented by the System.Threading.Thread class. We
can create multiple threads in our program by creating multiple instances
(objects) of this class.

– A thread starts its execution by calling the specified method and terminates
when the execution of that method gets completed. We can specify the
method name that the thread will call when it starts by passing a delegate of
the ThreadStart type in the Thread class constructor. The delegate
System.Threading.ThreadStart may reference any method which has the
void return type and which takes no arguments.

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Example below does not use Multithreading

Public Sub Main()
Fun1()
Fun2() The output of the program is:
Console.WriteLine("End of Main()")
End Sub
Fun1() writes: 1
Public Sub Fun1()
Fun1() writes: 2
Dim i As Integer Fun1() writes: 3
For i = 1 To 5 Fun1() writes: 4
Console.WriteLine("Fun1() writes: {0}", i) Fun1() writes: 5
Next Fun2() writes: 10
Fun2() writes: 9
End Sub Fun2() writes: 8
Public Sub Fun2() Fun2() writes: 7
Dim i As Integer Fun2() writes: 6
For i = 10 To 6 Step -1 End of Main()
Console.WriteLine("Fun2() writes: {0}", i)
Next
End Sub

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The method Fun2() only started its execution when Fun1() had completed its
execution. This is because when a method gets called, the execution control
transfers to that method. And when the method returns the execution starts
from the very next line of the code that called the method. i.e. the program
implicitly has only one execution path. Using multithreading, we can define
multiple concurrent execution paths within our program called threads.

For example, we can use threads so that the two methods Fun1() and
Fun2() may execute without waiting for each other to terminate.

Imports System.Threading
Public Sub Main()
Dim firstThread As New Thread(New ThreadStart(AddressOf Fun1))
Dim secondThread As New Thread(New ThreadStart(AddressOf Fun2))
firstThread.Start()
secondThread.Start()
Console.WriteLine("End of Main()")
End Sub

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Public Sub Fun1()
Here we have created two instances
Dim i As Integer of the Thread class and passed a
For i = 1 To 5 ThreadStart type delegate in the
constructor which references a
Console.WriteLine("Fun1() writes: {0}", i) method in our program.

It is important that the method
Next referenced in the Thread class
End Sub constructor, through the ThreadStart
delegate is parameter-less and has
no return type.
Public Sub Fun2()
We have to start the execution of a
Dim i As Integer thread by calling the Start() method
For i = 10 To 6 Step -1 of the Thread class.
Console.WriteLine("Fun2() writes: {0}", i) The output of the program would now
be interleaving Fun1 () and Fun2()

Next
End Sub
End Module
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Synchronization of thread in VB.NET
Note : Does VB6 support Multi – threading.
No. VB6 supports multiple single-threaded apartments. This means each individual thread
application ( i.e. an apartment ) can use only the same set of data. Data cannot be shared
and a thread cannot be run in the background.

To understand synchronization, 1st understand a multithreaded program without
synchronize method (Thread.join ( )) and then with Thread.join().

Public Class SquareClass Use this code to start the CalcSquare procedure on a new
Public Value As Double thread, as follows:
Public Square As Double
// code in a form, add a button and handle button click
Private Sub Button1_Click(ByVal sender As System.Object,_
Public Sub CalcSquare() ByVal e As System.EventArgs) Handles Button1.Click
Square = Value * Value Dim oSquare As New SquareClass()
End Sub t = New Thread(AddressOf oSquare.CalcSquare)
oSquare.Value = 30
End Class
t.Start()
End Sub

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We do not inspect the square value of the class, because it is not guaranteed to have
executed once you call the start method of the thread. i.e. there is no synchronization.

There are a 2 ways to synchronize
• By raising an event when the thread is complete.
• By using Thread. join().

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Method 1:
Public Class SquareClass
Public Value As Double
Public Square As Double
Public Event ThreadComplete(ByVal Square As Double)
Public Sub CalcSquare()
Square = Value * Value
RaiseEvent ThreadComplete(Square)
End Sub
End Class

// code in a form, add a button and handle button click
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click
oSquare = New SquareClass()
t = New Thread(AddressOf oSquare.CalcSquare)
oSquare.Value = 30
t.Start()
End Sub
Sub SquareEventHandler(ByVal Square As Double) _
Handles oSquare.ThreadComplete
MsgBox("The square is " & Square)
End Sub
End Class
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Method 2:
To perform synchronizations, VB.NET provides the
• SyncLock … End SyncLock statement and the Thread.Join method.

• SyncLock gains an exclusive lock to an object reference that is passed to it.
By gaining this exclusive lock you can ensure that multiple threads are not
accessing shared data.
• In order to gain lock find System.Type of object associated with each class.
The System.Type object can be retrieved using the GetType method:

Public Sub CalcSquare()
SyncLock GetType(SquareClass)
Square = Value * Value
End SyncLock
End Sub

Lastly, the Thread.Join method allows you to wait for a specific amount of
time until a thread has completed. If the thread completes before the timeout
that you specify, Thread.Join returns True, otherwise it returns False.

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The code using synchronize methods
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click
Dim oSquare As New SquareClass()
t = New Thread(AddressOf oSquare.CalcSquare)
oSquare.Value = 30
t.Start()
If t.Join(500) Then
MsgBox(oSquare.Square)
End If
End Sub
Thread.Abort stops a thread from executing. In above example, we can add another button on the
form that allows us to stop the process. To do this all we would have to do is call the Thread.Abort
method as follows:

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
t.Abort()
End Sub

This is where the power of multithreading can be seen. The UI seems responsive to the user
because it is running in one thread and the background process is running in another thread.
The cancel button immediately responds to the user's click event and processing stops
178

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