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Using VB.NET with ASP.NET Page

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Title: Using VB.NET with ASP.NET Page


1
Using VB.NET with ASP.NET Page
2
Chapter Objectives
3
Object-Oriented Programming
  • Programming statements, or code, combined into
    logical groupings, functions, event handlers, and
    procedures

4
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

5
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

6
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

7
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()

8
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

9
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

10
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

11
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

12
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

13
TaraStoreClass.vb (continued)
14
TaraStoreClass.vb (continued)
15
ClassVariables.aspx
16
ClassVariables.aspx (continued)
17
ClassVariables.aspx (continued)
18
Chapter5.dll
19
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

20
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

21
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

22
Variable Declaration (continued)
23
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

24
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
25
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"

26
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

27
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

28
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

29
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

30
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

31
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

32
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

33
Object Browser
34
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

35
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

36
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

37
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

38
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

39
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")

40
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

41
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

42
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

43
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

44
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)

45
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

46
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

47
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

48
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

49
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

50
Creating a Function
  • Public Class TaraStoreClass
  • Public Function GetStoreName() As String
  • Return "Tara Store"
  • End Function
  • End Class
  • GetTheFunction(New TaraStoreClass().GetStoreName)

51
Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (Page 239)
52
Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
53
Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
54
Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
55
Using Visual Basic .NET in a Web Page
SampleUsingVB.aspx (continued)
56
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

57
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

58
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

59
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)

60
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

61
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())

62
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

63
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
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