Transcript 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
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
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
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()
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
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
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
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
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
TaraStoreClass.vb (continued)
TaraStoreClass.vb (continued)
ClassVariables.aspx
ClassVariables.aspx (continued)
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)
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
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 individually
Response.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
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
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 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
Creating a Function
Public Class TaraStoreClass
Public 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
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Using Visual Basic .NET in a Web
Page SampleUsingVB.aspx
(continued)
Using Visual Basic .NET in a Web
Page SampleUsingVB.aspx
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Using Visual Basic .NET in a Web
Page SampleUsingVB.aspx
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Using Visual Basic .NET in a Web
Page SampleUsingVB.aspx
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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
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;
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
Introduction to C# (continued)
• C# Sample
String s1;
String s2 =
s2 += "Tara
s1 = s2 + "
Label1.Text
"Welcome to ";
Store";
!!!";
= 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);
Introduction to C# (continued)
• JScript Sample - this goes inline in the HTML
code view
<%@ Page Language="jscript" . . . %>
<%
// 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);
%>
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());
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
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