VB Net Topics Introduction to VB Net Creating

VB. Net

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

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

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 • Read. Line() – Reads a line from the user • Write. Line() – writes as line to the screen • Name spaces can be included in our code using the keyword imports • Eg: Imports System. Console

Data types and Operators in VB. Net • Data types – Integer, string, single, double, boolean, char • Operators – Arithmetic (+, -, *, /, , Mod) – Logical (Or, And) – Relational (=, <>, <, <=, >, >=)

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

If Else If (Condition) Then Statements executed if condition is true Else Statements executed if condition is false End. If We can also have Else If block in If Else statements

Select Case var Case 1 stmt 1 // executed if var = 1 Case 2 stmt 2 // executed if var = 2 Case Else stmt 3 // 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. Write. Line(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 Console. Writeline(a) a=a– 1 Loop While(a<>0)

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

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

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

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

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

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

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

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

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

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 – 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 • Un. Load

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

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 File. Stream is used for creating and manipulating files

Reader and Writer • Binary. Reader – This class has methods to read binary or raw data • Binary. Writer – This class has methods to write binary or raw data • Stream. Reader – This class has methods to read stream of data • Stream. Writer – 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 File. Stream class. This makes use of File. Mode and File. Access 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

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

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

Connection Object • Dim con as New Odbc. Connection(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 Odbc. Command(str. Cmd, con) • str. Cmd – is the select/insert/update/delete statement or exec <<stored. Proc>> command • Con is the connection object created in the first step • Properties – cmd. Command. Type – This can be either Text or Stored. Procedure

Command Methods • Cmd. Execute. Reader() – Returns one or more table row(s) – for select statement • Cmd. Execute. Scalar() – Returns a single value – for select statement with aggregate function • Cmd. Execute. Non. Query() – Used for executing stored procedure or insert/update/delete statements

Data Reader and Data Set • Data Reader – Dim dr as Odbc. Data. Reader – This dr holds the result set present in datareader object • Data Set – Dim ds as New Data. Set() – 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 Odbc. Data. Adapter(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