Using VB.NET with ASP.NET Page

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Using VB.NET with ASP.NET Page
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Chapter Objectives
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Object-Oriented Programming

• Programming statements, or code, combined into
  logical groupings, functions, event handlers, and
  procedures

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Object-Oriented Programming (continued)

• Objects and Classes
• create objects based upon a class
• An object is a set of related code that is
  compartmentalized and built upon these classes
• access the object across multiple Web pages
• Create an object
• the object definition, called the class
• creating an instance of the class
• use the class as the template for creating the
  new object

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Object-Oriented Programming (continued)

• Instantiation
• Declaring and initializing an object from a class
  
• You create objects from the same definition
• Public Class TaraStoreClass
• Private StoreName As String "Tara Store"
• End Class

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Object-Oriented Programming (continued)

• Restrict applications access to the class
• Public - interact with other objects outside of
  the base class
• Private - called only from within the base class
• Protected - called from within the base class,
  and within subclasses
• Subclass a class that inherits from a base
  class
• Friend - called anywhere from within the same
  application

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Object-Oriented Programming (continued)

• Instantiate an object based on the class
  definition
• Declare a variable
• keyword Dim - to store the object
• keyword New - to identify that this is an object
  based on a class definition
• Dim Ch5Class As New Chapter5.TaraStoreClass()

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Object-Oriented Programming (continued)

• Decision control structures - organize the order
  in which the code is executed
• Event handlers - execute when the event occurs
• Procedures - named grouping of one or more
  programming statements
• Parameters - values passed multiple values are
  separated in a comma delimited list within
  parentheses
• Functions - named grouping of programming
  statements that can return a value

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Object-Oriented Programming (continued)

• Properties
• Set the value of a variable defined within an
  object
• Identified by the object name, a period, and the
  name
• Assigned a default value within the object
  definition, or the value is set as undefined
• All new objects inherit the same properties as
  the original object definition

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Object-Oriented Programming (continued)

• Inheritance
• Derive the interface and behaviors from another
  class
• Inherits keyword allows you to inherit from
  another .NET class
• All objects are inherited from the System.Object
• Properties like ToString apply to most objects
• Encapsulation
• Inner workings of the object are maintained
  within the object

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Introduction to Visual Basic .NET

• Windows Application
• User interface is called the Form
• Windows Forms tab in the Toolbox
• Created from System.Windows.Forms
• Web Pages
• Code behind the page contains class definition
• Inherits keyword
• Create classes in a file, or code behind the page
• Import the class into the page
• Create a new object using the class

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Creating a Class TaraStoreClass.vb (Page 215)

• Create Chapter5 Web application, create images
  folder, import images, and data files
• Create the TaraStoreClass class
  (TaraStoreClass.vb)
• Modify the Code View Options
• Automatic outlining and add line numbers
• Create Ch5Class (in ClassVariables.aspx)
• Retrieve values inherited from TaraStoreClass
• View the IL using the ILDASM

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TaraStoreClass.vb (continued)
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TaraStoreClass.vb (continued)
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ClassVariables.aspx
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ClassVariables.aspx (continued)
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ClassVariables.aspx (continued)
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Chapter5.dll
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Variables

• Declaring a variable
• Declaration keywords, variable name, data type
• Data type identifies what kind of data the
  variable can store
• Process of reserving the memory space for the
  variable before it is used in the program
• Declare all variables before they are used

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Variable Declaration

• Where the variable is defined determines where
  the variable can be used within the application
• Scope where access variable
• Lifetime how long variable and its value
  persist in memory

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Variable Declaration (continued)

• Keywords specify the variable scope
• Private - available only to code within the local
  class
• Public - used outside the class
• Friend - used only within the current application
  or project

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Variable Declaration (continued)
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Variable Declaration (continued)

• Naming variables
• Descriptive name
• No commands or keywords
• Begin with a letter
• Do not use a period or space
• Avoid special characters except underscore
• Visual Basic .NET commands and variables are not
  case sensitive
• First letter of each word is usually capitalized

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Variable Declaration (continued) First Three
Characters Identify the Data Type
Data Type Prefix Sample Variable Name
Boolean Bln BlnMember
Byte Byt BytZero
Char Chr ChrLetter
Date Dat DatBirthdate
Double Dbl DblWeight
Decimal Dec DecProductPrice
Integer Int IntNumberProducts
Long Lng LngSalary
Single Sng SngAverage
Short Sho ShoYears
String Str StrLastName
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Assigning Values to Variables

• The assignment operator is the equal sign ()
• Remember Visual Basic .NET is NOT case sensitive.
  However, Visual Studio .NET will place Dim, As,
  and String in upper case characters
• Dim LastName, FirstName as String
• Dim StoreName As String "Tara Store"

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Constants

• A variable that does not change
• Examples - tax rates, shipping fees, and values
  used in mathematical equations
• Declare a constant
• Const keyword - Name is usually all uppercase
• When you declare a constant, you need to assign
  the value to the constant
• Const TAXRATE As Integer 8

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Concatenation

• Process of joining one or more strings
• Concatenation operator ()
• Can also use () only with strings
• Join a literal string, or the result returned
  from an expression, or a variable that contains a
  string
• Dim lblControlContent Ch5Class.StoreName.ToStrin
  g() _
• "ltbr/gt" Ch5Class.StoreEmail.ToString()
• lblContact.Text lblControlContent

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Data Types

• Reference types
• Strings, classes, arrays, collections, and
  objects
• Memory addresses stored in the managed heap
• Value types
• Referred to as primitive types or structures
• Stores the actual data in the stack
• Boolean and Char
• DateTime (Date in Visual Basic .NET)
• All numeric data types

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String

• Strings are variable in length
• Do not have to specify the number of characters
• Several built-in methods manipulate strings
• LCase and UCase - converts case to lower and
  upper
• Dim Password As String
• Password LCase(txtPassword.Value)
• LblPassword.Text Password

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Char

• Store a single text value as a number between 0
  and 65,535
• Represents a character in categories such as
  digit, letter, punctuation, and control
  characters

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Numeric

• Byte - stores an integer between 0 and 255
• Short - 16-bit number from -32,768 to 32,767
• Integer - 32-bit whole number
• Long - 64-bit number
• Real number data types
• Single - a single-precision floating point number
• Double - larger numbers than the single data type
• Decimal - up to 28 decimal places and often used
  to store currency data

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DateTime

• Dates between 01/01/0001 and 12/31/9999
• Formats are mm/dd/yyyy and hhmmss
• Enclosed within a pair of pound signs
• Dim MyBirthday As DateTime
• MyBirthday 3/22/2002

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Object Browser
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Boolean

• Two possible values True or False
• In binary math
• 1 represents true
• 0 represents false
• In Visual Studio .NET
• True value is converted to -1
• False value is converted to 0

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Using a Property to Retrieve and Set the Value of
a Variable

• Use a variable outside of a class
• Use the property function
• Declare the variable public
• Property methods
• Used to keep private variables
• To retrieve and set the variables value
• Set the value and retrieve them indirectly

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Using a Property to Retrieve and Set the Value of
a Variable (continued)

• ReadOnly prevents you from writing to the
  property
• WriteOnly allows the value to be changed, but not
  retrieved from the property
• Public ReadOnly Property NewStoreName() As String
• Public WriteOnly Property NewStoreName() ?
• As String

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Collections

• Data stored in structures called collections
• System.Collections namespace provides access to
  classes that manage data
• Each item is referred to as an element
• These five collections
• ArrayList, HashTable, and SortedList - access any
  element without having to rotate through the
  other elements
• Queue and Stack - rotate through the collection
  sequentially to locate an element

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The ArrayList

• Stores each item in sequential order
• Each item is indexed with a number
• Do not need to define the size of the ArrayList
• Each item is identified using an index number
  that indicates its position
• Zero-based - first item is at position 0
• ArrayList size of 3 means it has 4 items

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The ArrayList (continued)

• Create an ArrayList
• Dim StateAbbrev As New ArrayList
• StateAbbrev.Add("IL")
• StateAbbrev.Add("MI")
• StateAbbrev.Add("IN")
• Retrieve the value individually
• Response.Write(StateAbbrev(0))
• Insert an element into the first position and
  remove it
• StateAbbrev.Insert(0, "OK")
• StateAbbrev.Remove("OK")

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The ArrayList (continued)

• Properties and Methods
• Add and Remove - add or delete a single element
• Insert and RemoveAt - add and remove elements at
  a specific index position
• AddRange and RemoveRange - add or remove a group
  of elements
• IndexOf - find the position of the element in the
  list
• A value of -1 means the element was not found in
  the list.
• Count - identifies the number of items in the
  array
• which will be the largest index number plus 1.
• Clear - remove all of the elements

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The HashTables

• Creates the index of elements using an
  alphanumeric key like an encyclopedia
• keys - a collection of alphanumeric values
• values - a collection of elements
• Add and Remove method
• Items added using key and value pair separated
  with a comma
• Key passed with quotation marks
• Second parameter is the value

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Other Collections

• The SortedList Class - Indexed by both the key
  and the item so the index position will change
  frequently
• The Queue Class - sequential access to the
  elements
• Stores them in First In, First Out (FIFO)
• Roller coaster ride
• People in the first car are let out first
• The Stack class - sequential access
• Stores them in Last In, First Out (LIFO) order
• Line in a theatre, church, or crowded elevator
• First one to enter the room is the last one to
  leave

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Procedures

• Subprocedures
• Do not return values
• Cannot be used in an expression value
• Event Procedures
• Not executed until an event triggers the
  procedure
• Known as an event procedure
• Does not return a value
• Page_Load event triggered when the page is loaded
  
• Functions
• A block of code that is grouped into a named
  unit.
• Built-in functions inherit from a .NET Framework
  class
• User defined functions

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Subprocedures

• Subprocedures
• Other keywords - Public or Private, Exit Sub
• Sub SubprocedureName(parameters)
• Action and Control Statements
• End Sub
• Call keyword calls the procedure
• Call SubprocedureName(arguments)

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Event Procedure

• Event Names
• Based on object name and event name
• Identified with the prefix on and event name
• Underscore (_) separate object and event name
• Sub objectName_eventHandler? (sender as Object,
  e as EventArgs)
• action and control statements
• End Sub

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Functions

• Are declared
• Public functions - visible to all other functions
• Private functions - only available within the
  context where they are declared
• Public Function GetStoreName() As Integer
• 'This function returns an integer
• Return 23422
• End Function

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Passing an Argument to a Function

• A pair of parentheses follows with zero or more
  arguments, also known as parameters, which are
  passed to the function when it is called
• If no arguments are passed, you use an empty pair
  of parentheses
• If multiple arguments are used, you use a comma
  to separate each argument

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Returning a Value From a Function Exiting a
Function

• Keyword Return
• Identify the value returned to the function call
• Exiting a Function
• Exit Function keywords
• A jumping control jumping controls allow you to
  temporarily halt the execution of a code block,
  and move to another section of code outside the
  function

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Exiting a Function

• Public Function GetStoreName() As String
• Dim UserName As String
• UserName txtUserName.Text.ToString
• If UserName "Admin" then
• Return "Welcome Administrator!"
• Exit Function
• Else
• Return "Welcome!"
• Exit Function
• End If
• End Function

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Creating a Function

• Public Class TaraStoreClass
• Public Function GetStoreName() As String
• Return "Tara Store"
• End Function
• End Class
• GetTheFunction(New TaraStoreClass().GetStoreName)

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Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (Page 239)
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Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
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Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
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Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
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Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
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Introduction to C

• Syntax similar to JavaScript and C
• Compiled by the C compiler
• into the same managed Intermediate Language code
  that is also generated by the Visual Basic .NET
  compiler
• Base Classes and development environment are
  available across programming languages
• Access to the same Windows Form tools and
  ASP.NET Web Form tools

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Introduction to C (continued)

• Language Differences
• C is case sensitive
• Array using C, use square brackets around index
  position
• One or more statements enclose code in curly
  braces
• Assign a value to a variable, specify the data
  type first, then specify the variable name
• String StoreName "Tara Store"
• int counter 1

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Introduction to C (continued)

• Comments in C are similar to comments in
  JavaScript
• // This is a single line comment
• /
• This is a multiline comment
• Always document your code
• /
• Declare the variable public in C
• Use all lower case letters for the keyword public
• Declaration of variables

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Introduction to C (continued)

• C Sample
• String s1
• String s2 "Welcome to "
• s2 "Tara Store"
• s1 s2 " !!!"
• Label1.Text s1.ToString()
• J Sample (this is the sample shown in the book)
• String s1
• String s2 "Welcome to "
• s2 "Tara Store"
• s1 s2 " !!!"
• Label1.set_Text(s1)

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Introduction to C (continued)

• JScript Sample - this goes inline in the HTML
  code view
• lt_at_ Page Language"jscript" . . . gt
• lt
• // Write the message to the Web page
• var s1 String
• var s2 String "Welcome to "
• s2 "Tara Store"
• s1 s2 " !!!"
• Response.Write(s1)
• Response.Write(s3)
• gt

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Introduction to C (continued)

• StringBuilder Class Import System and
  System.Text
• C Sample
• StringBuilder s3 new StringBuilder()
• s3.Append("Welcome to ")
• s3.Append("Tara Store")
• s3.Append(" !!!")
• Label1.Text s3.ToString()
• J Sample (this is the sample shown in the book)
• StringBuilder s3 new StringBuilder()
• s3.Append("Welcome to ")
• s3.Append("Tara Store")
• s3.Append(" !!!")
• Label1.set_Text(s3.ToString())

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Summary

• Process of creating an object from a class is
  instantiation
• Create multiple classes within a single class
  file
• Assign a data type to a variable when the
  variable is created
• Properties set the value of a variable defined
  within an object
• Constants store values in variables that do not
  change within the application
• Concatenation operator is the ampersand

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Summary (continued)

• Each item in the collection is referred to by its
  index position
• Procedures organize the order in which the code
  is executed
• Event handlers execute code when an event occurs
• Functions return values
• C is a new programming language that can be used
  to create ASP.NET applications