VB.net

Introduction
 Visual Basic .NET (VB.NET) is an object-
oriented computer programming language
implemented on the .NET Framework.
 Everything in VB.NET is an object, including
all of the primitive types (Short, Integer,
Long, String, Boolean, etc.) and user-
defined types, events, and even
assemblies.
 All objects inherits from the base class
Object

Strong Programming Features
VB.Net
 Boolean Conditions
 Automatic Garbage Collection
 Standard Library
 Assembly Versioning
 Properties and Events
 Delegates and Events Management
 Easy-to-use Generics
 Indexers
 Conditional Compilation
 Simple Multithreading

Data Types Available in VB.Net
Data Type Storage Allocation Value Range
Boolean Depends on implementing platform True or False
Byte 1 byte 0 through 255 (unsigned)
Char 2 bytes 0 through 65535 (unsigned)
Date 8 bytes
0:00:00 (midnight) on January 1, 0001
through 11:59:59 PM on December 31,
9999
Decimal 16 bytes
0 through +/-
79,228,162,514,264,337,593,543,950,335
(+/-7.9...E+28) with no decimal point; 0
through +/-
7.9228162514264337593543950335 with
28 places to the right of the decimal
Double 8 bytes
-1.79769313486231570E+308 through -
4.94065645841246544E-324, for negative
values 4.94065645841246544E-324
through 1.79769313486231570E+308, for
positive values
Integer 4 bytes
-2,147,483,648 through 2,147,483,647
(signed)
Long 8 bytes
-9,223,372,036,854,775,808 through
9,223,372,036,854,775,807(signed)

Object
4 bytes on 32-bit platform 8 bytes
on 64-bit platform
Any type can be stored in a variable of
type Object
SByte 1 byte -128 through 127 (signed)
Short 2 bytes -32,768 through 32,767 (signed)
Single 4 bytes
-3.4028235E+38 through -1.401298E-45
for negative values; 1.401298E-45 through
3.4028235E+38 for positive values
String Depends on implementing platform
0 to approximately 2 billion Unicode
characters
UInteger 4 bytes 0 through 4,294,967,295 (unsigned)
ULong 8 bytes
0 through 18,446,744,073,709,551,615
(unsigned)
User-
Defined
Depends on implementing platform
Each member of the structure has a range
determined by its data type and
independent of the ranges of the other
members
UShort 2 bytes 0 through 65,535 (unsigned)

Data Types Default Value Size (bytes)
Char 0 2
Byte 0 1
Short 0 2
Integer 0 4
Long 0 8
Single 0.0 4
Double 0.0 8
Decimal 0.0 16
Boolean False 1
Date 1/1/0001 12:00:00 Am 8

Operators
Arithmetic +,-,*,/,^,,Mod
Relational =,<>,<,>,<=,>=
Logical And, or, not
Assignment =,+=,-=,/=,*=

Option Statements
 Option explicit on/off
 Option compare binary/text
 Option strict on/off

Option explicit on/off
 If option explicit on variable
declaration is compulsory.
 If it is off variable declaration is not
compulsory.
 By default it is on.

Option compare binary/text
 By default binary
 If option compare is binary
comparison is case sensitive.

Option strict on/off
 By default option strict is off

Conditional Statement
If condition then
End if
If condition then
else
End ifIf condition then
Else if condition then
End if

 Iif(expression, true, false)

Short circuit evaluation
 Andalso, orelse
 VB.NET also provide two logical operators
andalso, orelse that can be used to help
evaluate expression as efficiently as possible.
 The andalso operator is used to prohibit the
evaluation of second condition if the result of
the expression is known after evaluating the
1st operand.
 There is a similar case with the orelse
operator in this case if the 1st condition is true
then 2nd condition will not be evaluated and
operator return true.

Select case
 Select case variablename
 Case 1
 Case 2
 Case else
 End select

Looping statements
 Do……..loop
 While………end while
 For………..next
 For each………….next

Exit statement
 Exit for
 Exit do
 Exit while

Procedure and function in VB.NET
 Procedure and functions are block of code in
a program. They are also termed as
subprogram and are basically used to avoid
repetition of same code a number of times.
 By making use if procedures and functions
we save time there by making development
faster.

 Functions are almost similar to
subprocedure except that function can
return value to the calling procedure.
Function procedures re encloses
between function and end function
block. Function returns a value
whereas procedure does not return a
value.

Passing arguments to function and
procedures
 Call by value
 Call by reference

Call by value
 It is used to pass and argument by value.
 It indicated that the value of the variable
should not be modified by the call procedure
or function.
 Hence when a variable is passed using
byval keyword a copy of the variable is
created within the call procedure. Any
change made to the value of the variable will
affect the copy not the variable itself.

Call by reference
 It is used to indicate that the arguments are
passed Byreference not value. This means
that the call procedure can modify or change
the variable. By passing argument by
reference a procedure is given access to the
original value of the variable in its memory
location. As a result any changes made to
the argument within the call function will be
reflected in the calling procedure.

Access Specifier
 Private, Public
 By default it is private
 When declare with a public keyword
elements are available throughout the
current project and within a other project that
are referencing the current project.
 On the other hand if elements are declare as
private it can only used within the current
module.

Arrays , Enumeration and
structure
 Array is an entity that contains multiple variables of
the same data type.
 This variables are referred to by a single name.
 This variables are called as elements of an array.
 An array subscripts or index is used to access each
element of an array.
 Array in VB.NET are classified into single and multi
dimensional array.
 Length property gives the total number of elements
in an array.

Redim statement
 The redim keyword in VB.NET allows us to
change the size of array after they have been
declared.
 A redim statement can only be used within a
procedure and not at the module level.
 When the size of an array is modified using
Redim keyword the original contents of an
array is lost, however the contents can be
retain using the keyword Preserve with
Redim.

Multidimentional Arrays
 Rectangular Arrays – Rectangular arrays are
multidimetional arrays where the number of
elements in each row is same, which occupy
adjacent memory locations.
 Jagged Arrays – A jagged array is an array of
arrays. When we declare a jagged array, we
specify number of rows. Each row holds an
array, which can be of different length.

Enumeration
 Enumeration are used when we need
to refer the values of primitive types
such as byte, short, integer as
constants

Structure
 A structure is a composite user defined
datatype using which we can group data of
different data type together.
 A structure can be declared with in a module
but it cannot appear inside a procedure.
 A Statement can contain data members as
well as procedure and functions.
 The scope of the data members within a
structure is public.

Object oriented concepts in
VB.NET
 Abstraction
 Encapsulation
 Polymorphism
 Data Hiding
 Inheritance

Class
 A class is a representation or a template of
common attributes of behavior of objects.
 The content of a class are called members.
Based on a class instance are created which
are called objects.

Properties and Methods
 In VB.NET data members that describes as
an object are called fields or properties.
 The members which describes object
behavior are called methods.


Properties
 Properties are an extension of variables.
 They don’t denote storage location but
instead have accessor which specify
statements that can be executed to assign or
retrieve to or from the properties.
 A set accessor in a property declaration is
used to assign values.
 A get accessor is used to retrieve values of
the property.

Types of properties
 Write only properties – It must have set
accessor and Get accessor may be omitted
 Read only – It must have Get accessor, the
Set accessor may be omitted.
 Read / Write – This type of property must
have Get as well as Set accessor.

Constructor
 Constructor executes automatically every
time when an object is created.
 Constructors are typically declared public
and are used for initialised purpose.
 In VB.NET the lifetime of an object begins
when it is created with the New keyword.
 Constructor in VB.NET are written using sub
new()…. End sub

Destructor
 The lifetime of an object ends when it is
destroy or goes out of the scope.
 In VB.NET the destructors are written using
the finalize() method.
 Destructor are use for cleanup operations
such as releasing of memory that is no
longer required.

Method Overloading
 Overloading is the process of declaring the
methods of a class having same name but
different signature.
 The signature of the method comprises the
number and the types of arguments.
 In VB.NET functions, procedures,
constructors and properties can be
overloaded.

Inheritance in VB.NET
 It is a process of creating classed
based on existing classes.
 Inheritance is based on the principle of
code reuse.

Access Specifiers
 Public – All public elements of a class are
inherited by it’s derived classes.
 Private – Private elements of a class can’t be
inherited by derived classes.
 Protected – Protected access for elements
denote that elements may be used within the
derived class but not outside the derived
class.

 Friend – Friend access modifier is
used to denote that the elements
accessible throughout the program in
which the class is defined.
 Protected Friend – This access
modifier indicated that the elements
contain features of both protected and
friend modiers.

Abstract Class
 An abstract class can’t be used to create
objects.
 It is generally used as as template to derive
other classes. An abstract class typically
has abstract methods which are only
method declaration without any
implementation.
 In VB.NET all classes are inheritable.
 The mustinherit keyword makes the base
class as a abstract class

Final Classes
 Final classes in VB.Net are marked
with the notinheritable keyword.
 Final classes can’t have derive
classes but they can be use to create
objects.

Method overriding
 Overriding is the process of overriding the methods
or properties of a base class in a derived class.
 In case of method overriding the return type, name
and arguments of method in the derived class must
be the same as that of the method be overriden.
 When an object of derived class invokes the
overriden method it will be derive class
implementation that will be called.
 The base class method must be marked with
keyword overridable and derived class method
marked with keyword overrides.

Shadows keyword
 If we wish to hide the inherited method within
a derive class and invoke an overriden
version of the method then we use the
shadows keyword.
 Shadows keyword can’t be used with the
overloads keyword.

Mybase keyword
 Mybase keyword is used to refer to the base
class method in derived class, that has
overriden method of the base class.

Myclass keyword
 This keyword works opposite to the way in
which mybase keyword works.
 Assume that a base method is overriden in
derived class.
 If the object that is used to invoke the method
is of derived class then it is always the
derived class version of the method in
another method of the base class.
 Instead of derived class version we must use
myclass keyword.

Interfaces , Namespaces
 Interfaces are similar to classes except that they
have no implementation methods. Methods are
only declare within within an interface and don’t
contain any code.
 An interface can’t be instantiated it is typically
implemented be a class using implements keyword.
 An interface defines using
 Interface <interfacename>
 End interface

 A class can’t inherit from two other
classes but it can inherit a class and
implement an interface.
 Multiple inheritance is not supported in
VB.NET.
 However, it can be achieved with the
help of inherfaces.

Namespaces
 In VB.NET clas libraries are comprises of
namespaces.
 Namespaces are used to organise nested
entities such as other namespaces, classes,
interfaces and so on.
 Namespaces takes care of the way in which
program elements are expose to other
program with the help of various access
modifiers.
 Modules and classes are generally put inside
namespaces.

Collections
 A collection is term used to describe a means
of grouping and managing related entities.
 An VB.NET a collection is used to manage
the objects that are used to manage the
objects that are used by class.
 The simplest way to create a public instance
of type microsoft.visualbasic.collection in the
program.

Events
 Events are actions that have trigger either by
a user action, program logic or by the
system.
 Whenever an event occurs the user may
either ignore an event or deal with the event
with the help of suitable code.
 Procedure containing codes that will process
the events are called event handler.
 The syntax to create an event is :-
 Private/public/proceted event
eventname(argument list)

 Once declare an event can be activated with
the help of the raise event statement placed
inside a subprocedure.
 To process an event we may use any one of
the following approaches :-
◦ Use addhandler statement to provide a reference
to an event handler.
◦ Use withevents, with conjunction, withhandles
keywords.

Delegates
 Representative
 Pointer to function.
 In VB.NET a delegate is define as
representative of a function or a procedure it
holds a reference to a method.
 A delegate declaration must specify the
parameter or return type for the method
which it represents.
 VB.NET allows us to create two types of
delegate classes.

 Singlecast delegates
 Multicast delegates
 Single cast delegates are delegate classes
that are derived from delegate class.
 Multicast delegates are derived from
multicast delegate class.
 Single cast delegates contains an invocation
list with only method where as multicast
delegate contains invocation list with one or
more methods.

Multithreading
 Multithreading in VB.NET is accomplish
through the classes and interfaces in the
system.threading namespace.
 To create a new thread we pass a delegate
to the constructor of the system.threading
thread class.
 This delegate must point to a method that will
act as starting point for the thread.

Name property
 A thread can be given a name by
using name property of the thread
class.

Suspend and resume method
 The suspend and resume method of
system.threading thread class is used to
suspend an action of the thread for
indefined period.
 The thread can be resume using the
resume method.

Synchronisation
 When two or more threads in a multithreaded
application access common method or data
simultaneously there will be a conflict and as a
result important info could be lost or data will
become inconsistent.
 To avoid this it is necessary to have some kind of
mechanism in a multithreaded application that
allows methods or data to be access by one thread
at a time.
 Synchronisation is a process that allows thread to
access methods or data one thread at a time.
 We use Synclock keyword for it.

 The synclock ………. End synclock block
encloses the statement that are likely to
cost conflict in data and act as monitor thus
giving the calling thread exclusive lock.
 Because of this only one thread is given
priority to execute at any given time.

Monitor Class
 VB.NET provides a monitor class which
defines enter, try enter and exit methods.
 These methods of monitor class describe
below.
 Enter method :- This method acquires a
monitor lock for an object. This method may
block execution of other methods in the
current thread holds the lock.
 Try Enter :- Tries to acquire a monitor lock
without blocking.

 Exit :- This method release the monitor lock
on an object.
 Wait :- Wait method waits until another
thread passes notification method using the
PULSE method.
 Pulse :- Pulse method is used to notify
about the change in the state of an object to
a thread that is waiting.

Memory management in VB.NET
 In an automatic memory management
environment a garbage collector program
runs as a separate thread.
 The garbage collector frees memory that no
longer needed.
 VB.NET uses a garbage collector to
implement automatic memory management.

Garbage collector
 The garbage collector needs to know when objects
are no longer in use by an application.
 This information is given to the garbage collector
using concept called metadata.
 Every element in a VB.NET includes metadata that
describe it.
 By means of metadata the CLR knows the layout of
each object in memory.
 The JIT compiler and the CLR maintains a list of
active rules.
 This is then made accessible to the garbage
collector algorithm.

Dialog Boxes
 Modal – Open, Save, print
 Modeless – Find, replace.

Common Dialog Boxes
 Openfile
 Savefile
 Font
 Color
 Print dialog
 Print preview
 Pagesetup

 A dialogbox is a temporary window that
contain controls that can be used to display
information and messages to the user or to
accept the user input so that a specific
action can be carried out.

Types of Dialog Boxes
 Modal – A modal dialog box forces the user
to make a selection or perform a particular
action before proceeding with an application.
 For eg. If a modal dialog box is used to
display a message the user will not able to
switch another form unless and until the user
closes the dialog box.

 Modeless :- This dialog boxes let the user
switch to another form without having to
close the dialog box.
 Modeless dialog box allow user to continue
to work anywhere in the current application
while the dialog box is displayed.

Error handling in VB.NET
 Data Validation :- An application processes
information that user entered. Data validation
ensures that the data entered in the
application is accurate and of valid data type.
In winforms two data validation techniques
are supported
 A field level validation
 A form level validation

Field level validation
 Data in the field of the form are verified one at
a time after the user enters a value into a
particular field and moves on to the next field
on the form.
 Controls also support some methods and
events that are useful for verification and
validation data.
 Leave event :- When a form or a control
looses the focus or the cursor leaves the
control, the leave event is fire.

 Enter event :- This event is fire when the focus is
set to a field. This event can be used to check
whether the value entered in the previous field is
valid or not.
 Validating :- This event occurs when the control is
being validated. This event takes an argument of
type
◦ Cancelevent args
◦ The main property of the cancelevent args argument is the
cancel property.
◦ The cancel property can be set true or false to indicate
whether the event has to be canceled or not.
 Validated :- This event occurs after the validation of
the control is completed or after the validating event
is completed.

Keyboard events
 The main three keyboard events used in
validation are keypress, keydown, keyup
 A keypress event occurs when a keyboard
key is pressed while a control has focused.
The keypress event takes an argument of
type KeyPressEventArgs which represents
the character is composed when a key is
pressed.

Properties of keypresseventargs
 Handled – The value of this property indicates
whether the keypress event was handled or not.
 Keychar – This property represents the character
that correspond to the key press by the user.
 Key down/ Key up – These events are closely
related with the keypress events. The keydown
event occurs before keypress event as soon as the
user press a key and the keyup event occurs when
the user releases the key. The key down and keyup
events of types system.windows.forms.keyevent
args

Properties of keyeventargs
 Alt – It indicates whether the ALT key was
press or not.
 Control – It indicates whether ctrl key was
press or not.
 Shift - It indicates whether shift key was press
or not.
 Handled –
 Keycode – It will return keyboard code of the
key which when press triggers the keydown
and keyup events.

Exception Handling
 Exceptions are used to handle
abnormal/exceptional conditions that arises
while executing programs.
 Winforms include default exception that are
raised when an error occurs.
 Exceptions are used to handle runtime
errors.
 There are two different types of exception
classes supported in winforms,
System.exception and application.exception.

MDI
 Multiple Document interface
 A mdi application is made up of one MDI
parent form and one more child form.
 A MDI form is created in the same way as
we create a form, when the property
ISMDICONTAINER is set to true for a
window form it becomes a MDI form.

Collections Classes
 .NET provides the system.collections
namespace that contains various interfaces
and classes representing the collection of
objects. The advantage of using collection
classes :-
◦ Performance – Collection classes consist of
efficient algorithm.
◦ Similarity – Similar operation work on dissimilar
data types.
◦ Extensibility – We can extend the functionality of
collection classes for any new data type.

Collection Types
 Ordered collection
 Indexed collection
 Key collections

Ordered collection
 Classes that implement the I collection
interface fall under this category.
 In this category the insertion and deletion of
objects is order based i.e. the order in which
the elements are inserted controls, the order
in which they would be retrieve from the
collection. E.g. Stack Queue.

Indexed Collection
 Here the insertion and retrieval of elements
is index based i.e. elements can be retrieve
using O base numeric index.
 Such collections implement the I list
interface i.e. array, arraylist.

Key collections
 Here elements can be inserted and
retrieve using an associated key value
pairs.
 This classes implements the I
dictionary interface i.e. hashtable ,
sorted list.

Stack
 The collection namespace provides a stack
class, which provides Last In First Out way
to store and retrieve the elements.
 The operation by which an element is added
to the stack is called PUSH, and the
operation by which element is removed from
the stack is called POP.
 The member of the stack that refers last
element of the stack is called TOP.

Queue
 The collection namespace also provides a
queue class which provides First In First Out
way to store and retrieve the elements.
 The end at which first element is placed is
called front and the end at which last element
is placed is called rear.
 A new element get’s added at the end that is
at rear end and an element get removed from
front end.

Array List
 Array list class is similar to the array
class except that it’s size can grow
dynamically.

Hash table
 One of the most efficient known data
structure for fast look up is “HASH TABLE”.
 In a hash table we can store pair of values
and associated keys.
 The value are organised on the basis of the
keys.
 The keys can be used to retrieve the
corresponding values from the hash table.

GDI+
 .NET provides a set of GDI classes. This
classes allows programmers to draw
graphics or text without being require to
bother about the specification of the video
hardware.
 These classes are present in system.drawing
and system.drawing.drawing2D namespace.
 The GDI+ classes offer device independence
to our program.

 Device independence means that the same
program should work with the different
screens , keyboards and printers without
modifying the program.
 The GDI+ classes takes care of the
differences in hardware allowing a
programmer to concentrate on drawing.

Paint Handler
 The graphics class is a wrapper around the device
context.
 All methods used for drawing operations are
belongs to this class.
 This class is present in the system.drawing
namespace.
 When the onpaint eventhandler is called a
reference to the painteventargs object is passed to
it.
 The painteventargs class contains a property
access returns a reference to the graphics object.

FILE I/O
 We deal with files mainly for three purposes
getting properties of a file, reading and
writing data of primitive data types and
reading and writing data of user defined
types. For these purposes .NET provides
separate set of classes.
 The filesysteminfo and file classes are used
for performing file operations like creating ,
copying m deleting and moving of files.

 They also provide functions for getting
information of a file.
 The fileinfo and directoryinfo classes are
derived from the filesysteminfo class.
 Fileinfo class is used to perform an the file
operations that we can perform using the file
class.
 The DirectoryInfo class is used for creating ,
moving through directories and
subdirectories.

 The classes derived from the marshal Byref
object class are used for marshelling the
object across the application.
 Marshelling means creating an object in one
application and passing it’s state to another
application.

MarshalByRefObject
TextReader Stream Text Writer
String
Reader
Stream
Reader
String
Writer
String
Writer

 A stream is a sequence of bytes traveling
from source to destination or traveling over a
communication link.
 Two basic types of streams are InputStream
and OutputStream.
 An InputStream is used for read operation
while outputstream is used for write
operation.
 The streamReader class inherits a
textReader that reads characters from a
bytestream.
 The streamwriter clas inherits a textwriter for
writing a character to a stream.

Assembly
 Assemblies are building blocks of .NET application.
 Components are package into assemblies.
 Assembly can either be in a form of exe or dll files.
 To create the assembly.
 Programs->Ms visual studio 2005 -> Visual studio
tools -> Visual studio 2005 command prompt.
 Go to your application
 Vbc/t : library module1.dll

Inheritance Picker
 We can create a new form which is inherited
from another form.
 The environment has something called
‘inheritance picker’ that provides that
functionality.
 It is possible to create a base form with logic
and visual elements needed by all forms and
then have other forms inherits to get that
functionality.

 The logic and visual elements are
encapsulated in one location so that
changing the base form causes all the forms
inheriting form it to change automatically.
 This concept is called as ‘inheritance picker’.
 A form must be compiled in to an executable
file with the built command before it can be
used by the inheritance picker.
 Once that is done the menu options/ project/
add new item/inherited form allows the
addition of a form that inherits from another
form in the project.

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