An Introduction VB.NET2

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An Introduction VB.NET2

• ASP.NET
• http//sdetu/courses/csdc101/
• Lecture 07
• Tuesday, February 26, 2008

2
Agenda

• Functions
• Sub routines
• Classes

3
Branching Logic Controls

• Subroutines (sometimes called procedures)
• Functions
• The only difference between the two is that
  functions send information back to whatever
  called them, and subroutines don't.
• Subroutine
• Sub name (parameters)
• code
• End Sub

4
Example

• 4 sub Page_Load(obj as object, e as eventargs)
• 5 MultiplyNumbers(8,9)
• 6
• 7 MultiplyNumbers(4,12)
• 8
• 9 MultiplyNumbers(348,23)
• 10 end sub
• 11
• 12 sub MultiplyNumbers(intA as integer, intB as
  integer)
• 13 Response.Write(intA intB "ltbrgt")
• 14 end sub

5
Function Example

• 4 sub Page_Load(obj as object, e as eventargs)
• 5 Response.Write(MultiplyNumbers(8,9)
  "ltbrgt")
• 6
• 7 Response.Write(MultiplyNumbers(4,12)
  "ltbrgt")
• 8
• 9 Response.Write(MultiplyNumbers(348,23)
  "ltbrgt")
• 10 end sub
• 11
• 12 function MultiplyNumbers(intA as integer,
  intB as _
• 13 integer) as Integer
• 14 Return intA intB
• 15 end function

6
Two ways of Returning a value

• Using return statement
• Assigning the return value to the function itself
• 12 function MultiplyNumbers(intA as integer, intB
  as _
• 13 integer) as integer
• 14 MultiplyNumbers intA intB
• 15 end function

7
Optional Parameters

• VB.NET allows you to do this with the Optional
  keyword
• function MultiplyNumbers(intA as integer,
  _optional intB as__ integer 3) as Integer
• return intA intB
• end function
• Calling the above function
• MultiplyNumbers(8)
• MultiplyNumbers(8,9)

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Event Handlers

• Actions that may occur in your applicationa
  mouse click or a button press, for instance.
• You do this by creating an event handler. The
  syntax is identical to that for a subroutine.
• When an event is raisedmeaning the event has
  occurredit produces variables that describe the
  event.
• Your event handler can use these variables to
  figure out what to do.

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Example

• 1 lt_at_ Page Language"VB" gt
• 2
• 3 ltscript runat"server"gt
• 4 Sub Button_Click(Sender As Object, e As
  EventArgs)
• 5 Response.Write("You clicked the button!")
• 6 End Sub
• 7 lt/scriptgt
• 8
• 9 lthtmlgtltbodygt
• 10 ltform runat"server"gt
• 11 ltaspbutton id"btSubmit" Text"Submit"
• 12 runatserver
• 13 OnClick"Button_Click"/gtltpgt
• 14 lt/formgt
• 15 lt/bodygtlt/htmlgt

represents the object that raised the event.
contains any information specific to the event
that occurred.
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What is an Object?

• Objects are real world entities.
• Dosa
• Fried Maggi
• Teacher
• Etc
• Two characteristics of these are
• State
• Behaviour

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What is state of Objects?

• Dosa is cold.
• Dosas Temperature.
• Fried Maggi is too spicy
• Spice Level in Maggi
• State in software Objects are dependent on
• Variables.
• Objects Contained.

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Behaviour of an Object

• Teachers Phd
• Depends on Teachers research interest.
• Students exam preparation
• Depends on the Cricket match schedule.
• Behaviour of a software object is
• Functions Exposed by the object.

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Features of Object Orientation

• Encapsulation
• Hiding out stuff from others.
• Ex Consider Mail as an object, now you have your
  personal mails ?
• Modularity
• Imagine each student getting a room.
• A Room gives privacy and separates out behavior
  of these students.

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In Programming terms

• Encapsulation
• Controlling access to your Variables.
• Controlling access to your Methods.
• Modularity
• Source code of one program is independent.
• A software can be constructed from many such
  modules.

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Messages

• In a class if you sit alone, you may get sleep.
• So you interact with Next student. ?
• Objects cannot exist independently in vacuum.
• They may have to interact with some one. But
  How????

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In programming terms

• But objects are not complicated as humans.
• Messages are usually passed as parameters to the
  method exposed by the object.
• So Two Object communicate using behaviors.
• Now this Message can also be an object.

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Classes

• Classes form a template for creating objects.
• Why do you need classes?
• Classes give you a generic way of defining
  multiple objects.
• An Object in programming terms is an instance of
  a CLASS
• Didnt Understand????

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Example

• Note a separate class called Student.
• Student has two parts
• State (i.e. currently XYZ)
• Behaviour (i.e. returning Name and ID)
• Look at how the message is passed.
• Now with this template I can create n students
  who are similar to XYZ

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Class

• Everything in the .NET Framework and VB.NET is
  represented by classes
• Syntax
• Class name
• subroutines, functions, and properties
• End Class
• Any variables declared in a class are known as
  properties of the class.
• Access Levels
• Public Allows the members to be globally
  accessible.
• Protected - Limits the members access to the
  containing type and all classes derived from the
  containing type.
• Private- Limits the members access to only the
  containing type.

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Example

• 4 Class Clock
• 5 public Second as integer
• 6 public Minute as integer
• 7 public Hour as integer
• 8
• 9 sub SetTime(intSec as integer, intMin as
  integer, _
• 10 intHour as integer)
• 11 Second intSec
• 12 Minute intMin
• 13 Hour intHour
• 14 end sub
• 15 End Class
• 16
• 17 sub Page_Load(Sender as object, e as
  EventArgs)
• 18 dim objClock as new Clock
• 19
• 20 objClock.Second 60
• 21
• 22 end sub

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Example

• In your ASP.NET page, you could do the following
  
• Dim objClock as new Clock
• objClock.SetTime(60,4,12) objClock.Second 59
• Whats with new ?
• It's used to initialize a new object.
• One more form
• dim objClock as Clock New Clock

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Inheritance

• You don't have to create entirely new classes
  when there's a similar one that already does what
  you want.
• Class AnalogClock
• Inherits Clock
• private ClockWound as Boolean false
• sub WindClock()
• ClockWound true
• end sub
• End Class
• In your ASP.NET page, you could do the following
• dim objAnalogClock as new AnalogClock
  objAnalogClock.SetTime(60, 4, 12)
• objAnalogClock.WindClock

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