Chapter 5: ASP.NET Object-Oriented Programming

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Chapter 5 ASP.NET Object-Oriented Programming
Original slides by Kathleen Kalata Dave
Turton Modified by Meyer Tanuan
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Basic OOP terms

• Object
• A set of related code
• Properties
• Methods
• Class
• A definition of an object
• Like a cooking recipe
• Instantiation creating objects from a class
• Like creating cookies from a recipe
• Each inherits properties and methods from the
  class
• Can vary properties to create different, but
  similar, objects
• Oatmeal vs. chocolate chip cookies
• Checking vs. savings account

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Access Declarations

• Applied to properties, methods, Classes, etc.
• Private
• Accessible only within the class
• Protected
• Accessible within class sub-classes (inherit
  from the base class)
• Friend
• Accessible anywhere from within same assembly
• Public
• Accessible from outside of the class assembly
• Eg sharing User Control between assignment
  applications

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Methods or procedures

• Both accept parameters
• Values can be passed to procedure
• Public Sub SetWeightTons(ByVal newValue As
  String)
• ByVal - pass value of source variable (.NET
  default)
• ByRef - pass address of source variable
• 2 types of procedures (aka methods) (camelCase)
• Functions
• Return a value using return keyword
• Subs
• Do not return a value
• commonly used for event handlers
• Premature end of procedure Exit Sub, Exit
  Function
• Use () after procedure call, even if not passing
  any parameters required in C, but not in VB.NET

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Class example Using Procedures

• Public Class FreightCar
• Private weightTons as Integer
• Public Function getWeightMetric() As Integer
• Return weightTons 0.91
• End Function
• Public Sub setWeightMetric(ByVal newValue As
  Integer)
• weightTons newValue / 0.91
• End Sub
• End Class

weightTons, being private, is not accessible
outside the class The procedures are public,
used to access the freight car's
weight. Programmer control store in imperial,
deliver in metric
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Properties

• Used to indirectly access a variable
• Can have a set and/or a get action
• Set
• Sets the variable to the given value
• Get
• Returns the value of the variable
• When property is to right of "", get assumed
• When property is to left of "", set assumed

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Class example Using Property
Note underscore on Private variable allows you
to have a property with the same name

• Public Class FreightCar
• Private _weightTons as Integer
• Public Property weightMetric() As Integer
• Set(ByVal newValue As Integer)
• _weightTons newValue / 0.91
• End Set
• Get
• Return _weightTons 0.91
• End Get
• End Property
• End Class

Weight is stored in Imperial measures, but
delivered and reset in metric
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Using Class Property

• Dim myCar As New FreightCar
• (Instantiate an object of type FreightCar)
• myCar.weightMetric 7388
• (Set action assumed)
• lblCarWeight.Text myCar.weightMetric.ToString()
• (Get action assumed)
• (notice using ToString method of Integer class)

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Constructors

• Methods executed when an instance of a class is
  created
• Use parameters to pre-set private variables
• Default Constructor
• Used when no parameters are passed
• Assumed present when no constructors coded
• Must explicitly define when other constructors
  present
• Can have multiple constructors
• Which to use
• Type sequence of passed parameters

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2-Constructor Example
Public Class FreightCar Private _type as
String "boxcar" Private _weight as Integer
"1200" ' constructor initialise type/weight at
instantiation Public Sub New(ByVal type as
String, ByVal tonnes as Integer) _type
type _weight tonnes / 0.91 End Sub '
default constructor use default type/weight from
class Public Sub New() ' default End
Sub ' properties to return weight or car type
Public Property weightMetric() as Integer
. Public Property type() as String
. End Class
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Using Constructors- which constructor to use
depends on parameter type order- have one with
String, Integer and one with no parameters
Dim oilTanker as New FreightCar("tanker", 1600) '
use 1st constructor Dim oilTanker as new
FreightCar() ' use default constructor Or
oilTanker.type "tanker" oilTanker.weightmetr
ic 1600 lblMessage.Text "type of car "
oilTanker.type "ltbr /gt" lblMessage.Text
"weight, loaded "oilTanker.weightMetric.ToString
() Later creating/using a collection of these
new objects with ArrayList
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Inheritance

• Problem
• A class has almost everything you need
• Need 1 or 2 more properties, methods
• Define a subclass
• Inherit class's properties methods
• Add (or override) methods, properties,
  constructors to subclass
• Use new class instead of original one

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Inheritance example

• Public Class MyArray
• Inherits ArrayList
• ' place new methods, properties here
• End Class
• ' using it, in another program
• Dim category as New MyArray()
• category.Clear()
• category.Add("milk")
• category.Add("soda")
• lstCategory.DataSource category
• lstCategory.DataBind()
• Your MyArray class inherited Add() and Clear()
  methods from its ArrayList parent

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Variable Types
intCount
75

• Primitive Types
• Reference is address of value in the stack
• Variable has fixed defined size cannot change
  that
• Reference Types
• Reference is address of a pointer to object in
  the heap (area managed by garbage collector)
• Address is a fixed-length item
• Garbage collector can move object data
• Program still ref's address location
• Which could have a different value
• Variables memory requirements vary
• Properties, methods vary by object
• Value varies in size
• May be a collection varying number of elements

strName
2ce8f965
Count 4 Value Tara Trim()
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Variables

• Naming
• Begin with a letter/underscore, follow w/
  letters, numbers, underscore
• No spaces or periods in name, avoid special
  characters
• Declaring method or local variables
• Dim
• accessible only within the scope of the program
  block
• Method body, loop body, if body
• Declaring instance variables
• Private (default if Dim is used)
• Only available within the class
• Public
• Are accessible outside the class

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Primitive Data Types

• Byte
• 8 bits 0 to 255
• Short
• 16 bits -32,768 to 32,767
• Integer
• 32 bits
• Long
• 64 bits
• DateTime
• mm/dd/yyyy hhmmss

• Single
• Floating point number
• Double
• Larger floating point number
• Decimal
• 28 decimals currency
• Char
• 16 bits 0 to 65,535
• Boolean
• True/False

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String Methods

• xx.TrimStart(), xx.TrimEnd(), xx.Trim()
• Remove blanks from left, right, both ends
• xx.Replace("x", "y")
• Replace instances of char/string x with
  char/string y
• xx.Substring(x,y)
• Return substring starting at index x, for y
  characters

• xx.IndexOf("", y)
• Return index of given string, starting search at
  index y
• xx.ToLower() xx.ToUpper()
• Convert string to lower or upper case

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Collections

• An object that can store other objects (elements)
• Elements can be any data type
• Collection types
• ArrayList indexed collection of same data type
• HashTable 2-part elements key value
• SortedList key/value pair, indexed, ordered by
  key
• Queue sequential access FIFO
• Stack sequential access LIFO

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ArrayListDim nameList as New ArrayList

• Zero-based indexing to each item
• Properties
• Count
• number of elements in array
• Methods
• Add(), Remove()
• add/remove an item
• Insert(), RemoveAt()
• add/remove item at specific index location
• AddRange(), RemoveRange()
• Add/remove a group of items
• IndexOf()
• Returns index of given element, -1 if not found
• Clear()
• Remove all elements

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ArrayListcan contain complex objects

• Dim railCars as New ArrayList
• railCars.Add(New FreightCar("flatbed", 1000))
• railCars.Add(New FreightCar("tanker", 2600))
• ' accessing properties of each element
• lblFleet.Text railCars(0).type ", "
  railCars(1).type
• ' using with a CheckBoxList
• chkFleet.DataSource railCars
• chkFleet.DataTextField "type"
• chkFleet.DataValueField "weightMetric
• chkFleet.DataBind()

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HashTableDim nameTitle as New HashTable

• Indexed by an alphanumeric key (no sorting)
• Key is first parameter of each element
• Value is second parameter of each element
• Properties
• Count number of elements in array
• Keys returns a collection of all the keys
• e.g., myArrayList.Add(myHash.Keys)
• Methods
• Add(key, value)
• Clear()
• Item()
• Get or set the value at the given key e.g.,
  myHash.Item(15)
• Implicit Item reference e.g., myHash(10)
• ContainsKey(), ContainsValue()
• Boolean return type determine if list contains
  given key or value

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HashTable Sample

• Dim myHash As New Hashtable
• myHash.Add(12, "FGH")
• myHash(10) "ABC"
• myHash.Item(15) "XYZ
• lblHash.Text myHash.Item(10) ", "
  myHash(12) ", " myHash(15)

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SortedList

• Similar to HashTable
• However
• Indexed by both key and zero-based index
• So can use some index-based methods of ArraryList
• Index position changes as items added
• Automatically sorts on key
• Some Methods
• GetKey(), GetByIndex()
• IndexOfKey(), IndexOfValue()

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SortedList Sample

• Dim mySortedList As New SortedList
• mySortedList.Add(12, "FGH")
• mySortedList(10) "ABC"
• mySortedList.Item(15) "XYZ"
• ' use index 0, 1, 2 to access sorted list of keys
• lblSorted.Text mySortedList.GetKey(0).ToString()
  ", " _
• mySortedList.GetKey(1).ToString() ", "
  _
• mySortedList.GetKey(2).ToString()
• lblSorted.Text "ltbr/gt" mySortedList.GetByInde
  x(0) ", " _
• mySortedList(12) ", "
  mySortedList.GetByIndex(2)

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Queue

• Sequential access to elements
• First in, first out (FIFO)
• Properties
• Count
• Number of elements in the queue
• Methods
• Enqueue()
• Add an item to the tail of the queue
• Dequeue()
• Remove return the item at the head of the queue
• Clear()
• Remove all elements from the queue
• Peek()
• Look at the element at the head of the queue,
  w/out removing
• Contains()
• Boolean true if the given element is in the queue

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Stack

• Sequential access to elements
• Last in, first out (LIFO)
• Properties
• Count
• Number of elements in stack
• Methods
• Push()
• Add an item to the top of the stack
• Pop()
• Remove return the item at the top of the stack
• Clear()
• Remove all elements from the stack
• Peek()
• Look at the element at the top of the stack,
  w/out removing
• Contains()
• Boolean true if the given element is in the
  queue