VB .Net

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VB .Net
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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

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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

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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

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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

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Creating VB .Net Project in VS 2005

• Open Visual Studio 2005
• Click File -gt New -gt 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

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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

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Data types and Operators in VB .Net

• Data types
• Integer, string, single, double, boolean, char
• Operators
• Arithmetic (,-,,/,\,Mod)
• Logical (Or, And)
• Relational (,ltgt,lt,lt,gt,gt)

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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

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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

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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

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For Loop

• For ltltvargtgt start To end Step ltltvalgtgt
• 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

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Do While Loop

• Do While(altgt0)
• Console.Writeline(a)
• a a 1
• Loop
• 2. Do
• Console.Writeline(a)
• a a 1
• Loop While(altgt0)

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Do Until Loop

• Do Until(a0)
• Console.Writeline(a)
• a a 1
• Loop
• 2. Do
• Console.Writeline(a)
• a a 1
• Loop Until(a0)

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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

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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

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Subroutines and Functions

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

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Constructor

• Used for initializing private members of a class
• Name of the constructor should be New() always
• Can have zero or more parameters
• 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

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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.

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Collections

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

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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

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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

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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

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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

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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

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Windows Application

• File -gt New -gt 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

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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

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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

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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

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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

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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

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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

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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

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File Handling

• 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

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Operations on a file

• Create
• Move
• Copy
• Replace
• Read
• Write
• Delete

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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

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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

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Command Object

• Dim cmd as New OdbcCommand(strCmd,con)
• strCmd is the select/insert/update/delete
  statement or exec ltltstoredProcgtgt command
• Con is the connection object created in the first
  step
• Properties cmd.CommandType
• This can be either Text or StoredProcedure

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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

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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

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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