using vb.net with asp.net page

Using VB.NET with ASP.NET Page

Chapter Objectives

Object-Oriented Programming

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

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


• Instantiation– Declaring and initializing an object from a

class – You create objects from the same definition

Public Class TaraStoreClassPrivate StoreName As String = "Tara Store"

End Class


• 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


• 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()


• 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


• 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


• 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

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

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

TaraStoreClass.vb (continued)

ClassVariables.aspx

ClassVariables.aspx (continued)

Chapter5.dll

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

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

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

Variable Declaration (continued)

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

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

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"

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

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.ToString() _

& "<br/>" & Ch5Class.StoreEmail.ToString()

lblContact.Text = lblControlContent

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

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

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

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

DateTime

• Dates between 01/01/0001 and 12/31/9999

• Formats are mm/dd/yyyy and hh:mm:ss

• Enclosed within a pair of pound signs

Dim MyBirthday As DateTime

MyBirthday = #3/22/2002#

Object Browser

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

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 variable’s value

• Set the value and retrieve them indirectly

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

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

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

The ArrayList (continued)

• Create an ArrayList

Dim StateAbbrev As New ArrayList

StateAbbrev.Add("IL")

StateAbbrev.Add("MI")

StateAbbrev.Add("IN")

• Retrieve the value individuallyResponse.Write(StateAbbrev(0))

• Insert an element into the first position and remove it

StateAbbrev.Insert(0, "OK")

StateAbbrev.Remove("OK")

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

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

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

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

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)

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

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

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

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

Exiting a Function

Public Function GetStoreName() As StringDim UserName As String

UserName = txtUserName.Text.ToString

If UserName = "Admin" then

Return "Welcome Administrator!"

Exit FunctionElse

Return "Welcome!"

Exit FunctionEnd If

End Function

Creating a Function

Public Class TaraStoreClassPublic Function GetStoreName() As String

Return "Tara Store"

End Function

End Class

GetTheFunction(New TaraStoreClass().GetStoreName)

Using Visual Basic .NET in a Web Page SampleUsingVB.aspx (Page

239)

Using Visual Basic .NET in a Web Page SampleUsingVB.aspx

(continued)

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

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;


• 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


• C# SampleString 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);


• JScript Sample - this goes inline in the HTML code view

<%@ Page Language="jscript" . . . %>

<%// Write the message to the Web pagevar s1 : String;var s2 : String = "Welcome to ";s2 += "Tara Store";s1 = s2 + " !!!"; Response.Write(s1);Response.Write(s3);%>


• 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());

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

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

using vb.net with asp.net page

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