Ty bca-sem-v-introduction to vb.net-i-uploaded

Prof. Prachi Sasankar.
Dept. of Comp.Science
Sadabai Raisoni Women’s College, Nagpur

Introduction
 VB.Net is developed by Microsoft
 It is Visual Basic for .Net Platform
 Ancestor of VB.Net is BASIC
 In 1991, Microsoft added visual components to BASIC
and created Visual Basic
 After the development of .Net, VB was added with more
set of controls and components and thus evolved a new
language VB.Net
Prof. Prachi Sasankar. TY-BCA-Visual Database Programming

Topics
 Introduction to VB .Net
 Creating VB .Net Project in VS 2005
 Data types and Operators in VB .Net
 String Functions
 Conditions (If Else, Select Case)
 Loops (Do While, Do Until, For)
 Classes, Objects
 Sub routines and Functions
 Constructor and Destructor
 Windows Application
 Collections
 File Handling
 Exception Handling
 Data base connectivity
Prof.Prachi Sasankar. TY-BCA-Visual Database Programming

Pros and Cons
 Pros
 Faster development of programs
 Rich set of controls
 Object Orientation of language enhances
modularity, readability and maintainability
 Cons
 Debugging larger programs is difficult, due to the
absence of an effective debugger

Features of VB .Net
 Object Oriented Language
 We can drag controls from the tool bar and drop
them on the form and write code for the controls
 Runs on the CLR (Common Language Runtime)
 Release of unused objects taken care by the CLR

Creating VB .Net Project in VS 2005
 Open Visual Studio 2005
 Click File -> New -> Project
 Choose Language as VB .Net
 Choose Type (Either Console Application or what ever
we want)
 Give the path under which the project need to be saved
 Click OK

Input and Output
 Under the namespace System there is a class called Console
 Console has 2 methods
 ReadLine() – Reads a line from the user
 WriteLine() – writes as line to the screen
 Name spaces can be included in our code using the keyword
imports
 Eg:
Imports System.Console
 EX:
 Dim I as Integer
I = console.ReadLine() ‘ Gets the value from user and stores it in
variable I
 Console.WriteLine(I) ‘Displays the value of I

Data types and Operators in VB
.Net
 Data types
 Integer, string, single, double, boolean, char
 Operators
 Arithmetic (+,-,*,/,,Mod)
 Logical (Or, And)
 Relational (=,<>,<,<=,>,>=)
Prof.Prachi Sasankar. TY-
BCA-Visual Database Programming

String Functions
 Len(str) – Length of the string str
 Str.Replace(“old”,”New”) – Replaces Old with New in
the string Str
 Str.Insert(pos,”string”) – Inserts the string specified at
the position pos in the string Str
 Trim(str) – Removes the leading and trailing spaces in
the string str
Prof.Prachi Sasankar. TY-
BCA-Visual Database Programming

If Else
If (Condition)
Then
Statements executed if condition is true
Else
Statements executed if condition is false
EndIf
We can also have Else If block in If Else statements
 If (a=0)
 Then
 Console.Writeline(“Zero”)
 Else If(a<0)
 Then
 Console.Writeline(“Negative”)
 Else
 Console.Writeline(“Positive”)
 EndIf

Select Case
Select Case var
Case 1
stmt1 // executed if var = 1
Case 2
stmt2 // executed if var = 2
Case Else
stmt3 // executed if var is other than 1 and 2
End Select

For Loop
For <<var>> = start To end Step <<val>>
Statements
Next
Eg
For I = 1 To 10 Step 2
Console.WriteLine(I)
Next
Here the values printed will be 1,3,5,7,9

Do While Loop
1. Do While(a<>0)
Console.Writeline(a)
a = a – 1
Loop
2. Do
a = a – 1
Loop While(a<>0)

Do Until Loop
1. Do Until(a=0)
a = a – 1
Loop
2. Do
a = a – 1
Loop Until(a=0)

Class
 Software structure that is important in Object
Oriented Programming
 Has data members and methods
 Blue print or proto type for an object
 Contains the common properties and methods of an
object
 Few examples are Car, Person, Animal
 Class Person
1. Properties: Name, Height, Weight etc
2. Methods: Run, Walk, Speak

Object
 Instance of a class
 Gives Life to a class
 Ram is an object belonging to the class Person
 Ford is an object belonging to the class Car
 Jimmy is an object belonging to the class Animal
 Public Class Test
 Dim a As Integer
 Sub Print()
 Console.WriteLine(“Hello”)
 End Sub
 Public Function add(ByVal a as Integer, ByVal b as Integer) as Integer
 Return (a+b)
 End Function
 End Class

Subroutines and Functions
 Subroutines
 Does not return any value
 Can have zero or more parameters
 Functions
 Always Returns some value

Constructor
 Used for initializing private members of a class
 Name of the constructor should be New() always
 Does not return any value. So they are sub routines
 Need not be invoked explicitly. They are invoked
automatically when an object is created
 A class can have more than one constructor
 Every constructor should differ from the other by
means of number of parameters or data types of
parameters
 Constructors can be inherited

Destructor
 Used for releasing memory consumed by objects
 Name of the destructor should be Finalize() and the
method is already defined in CLR. So we can only
override it.
 Does not return any value. Hence it is a subroutine
 Does not accept any parameters
 Only one destructor for a class
 Destructors are not inherited
 No need of explicit invocation. They are called when
the execution is about to finish.

Collections
 Array List
 Sorted List
 Hash Table
 Stack
 Queue
 These can be accessed via the System.Collections
namespace

Array List
 Array List is a dynamic array
 Its size grows with the addition of element
 Searching is based on the index
 Sequential search is performed on elements
 Hence it is slow
 Occupies less space
 Dim Arr as New ArrayList()
 Arr.Add(1)
 Arr.Add(2)
 The above code adds two elements 1 and 2 to the array list Arr
 To access individual element, Arr.Item(1) – fetches 2
 It is a zero based collection

Sorted List
 Elements are stored as key value pairs
 They are sorted according to the key
 Search is based on index as well as on keys
 Hence faster than Array List
 Occupies Medium amount of space
 Keys cannot be duplicate or null
 Values can be duplicated and also can be null
 Dim Sl as New SortedList()
 Sl.Add(1,”One”)
 Sl.Add(2,”Two”)
 Sl.Item(1) // fetches 1
 Sl.GetKey(1) //fetches the 1st Key,I.e. 1

Hash Table
 Hash table stores data as a key value pair
 Here the keys can be duplicated
 Search is based on the hash of key values
 Very fast way of searching elements
 Occupies large space
 Dim ht As New Hashtable()
 ht.Add(1, “Ram”)
 ht.Add(2,”Raj”)
 ht.Item(2) // fetches Raj

Stack
 Stack is a data structure where elements are retrieved in the
order opposite to which they are added
 It implements LIFO (Last In First Out) algorithm
 Its method called Push() is for adding elements
 Its method Pop() is for removing elements
 Dim stack As New Stack(5)
 Dim i As Integer
 For i = 1 To 5
 stack.Push(i)
 Next
 For i = 1 To stack.Count
 WriteLine(stack.Pop())
 Next

Queue
 Queue is a data structure where elements are retrieved in
the same order in which they are added
 It implements FIFO (First In First Out) algorithm
 Its method called Enqueue() is for adding elements
 Its method called Dequeue() is for removing the elements
 Dim queue As New Queue(5)
 Dim i As Integer
 For i = 1 To 5
 queue.Enqueue(i)
 Next
 For i = 1 To queue.Count
 WriteLine(queue.Dequeue())
 Next

Windows Application
 File -> New -> Project
 Select Language as VB .Net
 Select .Net template as Windows Application
 Give the path where the application need to be saved
 A application opens up with a Form

Forms and other controls
 Form is a container for other controls
 We can place the following in a form
 Label
 Text Box
 Check Box
 Radio Button
 Button
 Date Picker
 And more…

Properties and Events
 Every Control has a set of properties, methods and events
associated with it
 Eg Form
 Properties
 Name (program will use this name to refer)
 Text (title of the form)
 Methods
 Show
 Hide
 Close
 Events
 Load
 UnLoad
 If we hide a form, it is still in the memory. It can be shown at any time.
 If we close a form, it is erased out of the memory. Same as destroying an
instance of the form. We need to recreate it if needed to see it again.

Exception Handling
 Exception is Run time error
 It is not known at the compile time
 Examples of exceptions
 Divide by zero
 Accessing non existing portion of memory
 Memory overflow due to looping
 In VB .Net, exception is handled via Try Catch
Mechanism

Try Catch Finally
Try
Suspicious code that may throw an exception to be written
here
Catch ex As Exception
What to be done if exception occurs to be written here
Finally
Optional portion which will be executed irrespective of the
happening of exception to be written here. Can contain
code for releasing unnecessary space
 Catch block with Specific exception to be given first and then
the generic type Exception

File Handling
 In the System Namespace, the IO class has several
subclasses for file handling, text processing etc
 Classes File, Directory are used for creating, deleting
file or folders and also has methods to play with them
 Class FileStream is used for creating and manipulating
files

Reader and Writer
 BinaryReader
 This class has methods to read binary or raw data
 BinaryWriter
 This class has methods to write binary or raw data
 StreamReader
 This class has methods to read stream of data
 StreamWriter
 This class has methods to write stream of data
 Stream is a channel through which an object (file
in this case) is accessed

File Handling
 Open the file using FileStream class. This makes use of
FileMode and FileAccess enumeration to specify how to
open a file (for creating a new file or opening an existing
file) and whether the file is read only or write only or read
write
 Associate a reader for the stream
 Read the file and do the manipulations
 Open a file stream for writing
 Associate a writer
 Write contents to file
 Close the stream, so that it will be released back to the memory pool

Operations on a file
 Create
 Move
 Copy
 Replace
 Read
 Write
 Delete

Database Connectivity
 Following are important to get connected to the database
and perform operations
 Connection Object
 Command Object
 Operation on the Command Object
 Using Dataset and Data adapter
 Using Data Reader
 If we use data adapter, it is called as disconnected
architecture
 If we use data reader, it is called as connected architecture
 Connected Architecture – An active connection to the database is
required. Connection need to be opened and closed explicitly
 Disconnected Architecture – Connection management is done internally.

Connection Object
 Dim con as New OdbcConnection(connectionstring)
 Where connectionstring is a string that contains
details about the server where the database is located,
the name of the database, user id and password
required for getting connected and the driver details

Command Object
 Dim cmd as New OdbcCommand(strCmd,con)
 strCmd – is the select/insert/update/delete statement or exec
<<storedProc>> command
 Con is the connection object created in the first step
 Properties – cmd.CommandType
 This can be either Text or StoredProcedure
Command Methods
 Cmd.ExecuteReader() – Returns one or more table row(s) –
for select statement
 Cmd.ExecuteScalar() – Returns a single value – for select
statement with aggregate function
 Cmd.ExecuteNonQuery() – Used for executing stored
procedure or insert/update/delete statements

Data Reader and Data Set
 Data Reader
 Dim dr as OdbcDataReader
 This dr holds the result set present in datareader object
 Data Set
 Dim ds as New DataSet()
 ds holds the result of select statement
 Data adapter is used to fill the data set
Data Adapter
 Data adapter fills in the data set with the result of the select query
 Dim da as New OdbcDataAdapter(cmd)
 Cmd is the command object created
 da.Fill(ds) fills the dataset
 The data set can be set as a data source for various controls in the
web form or windows form

Connectivity:
 For MS SQL server we have corresponding Connection, Command, datareader and data adapter object
 They are:
 SqlDataReader
 SqlDataAdapter
 SqlConnection
 SqlCommand
 For My SQL we have corresponding Connection, Command, datareader and data adapter object
 They are:
 OdbcDataReader
 OdbcDataAdapter
 OdbcConnection
 OdbcCommand
 For Oracle server we have corresponding Connection, Command, datareader and data adapter object
 They are:
 OracleDataReader
 OracleDataAdapter
 OracleConnection
 OracleCommand
 For MS Access/ Excel we have corresponding Connection, Command, datareader and data adapter object
 They are:
 OledbDataReader
 OledbDataAdapter
 OledbConnection
 OledbCommand

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