Transcript chapt6 (slides 48-53)

6
Chapter
Six
Using Visual Basic 6.0 to
Create Web-Based
Database Applications
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Chapter Objectives
• Learn about the Visual Basic development
environment
• Learn about the components of a Visual
Basic database application
• Create a Visual Basic application using the
ADO data control to display database data
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Chapter Objectives
• Create programmatic data controls to
process data in a Visual Basic program
• Create a Visual Basic ActiveX document
that is run from a Web page
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ActiveX Documents
• ActiveX documents
– A program that users can download from a Web
site and install on their computers
Figure 6-1: Installing an ActiveX document
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Overview of Visual Basic
• Visual Basic
– Can be used to create almost any kind of
Windows-based program
– An event-driven programming language
• Program statements execute in response to user
actions or to system actions
Components of a
Visual Basic Program
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• Project file
– Specifies properties of the program and the names
of the individual component of the program
• Form
– Main components of a VB project
– Composed of the visible interface that the user sees
and interacts with, and the associated code that
responds to user and system actions
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Components of a
Visual Basic Program
• Standard module
– Contains only code
– Used to store declarations for variables that are used in
multiple forms
• Procedure
– Manipulates variable values
• Function
– Returns a single value based on parameters that are
passed to the function
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Components of a
Visual Basic Program
• Controls are the visible items on a form
Figure 6-2:
Form
Controls
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Visual Basic Projects
• When VB is started, a new project is
created, which corresponds to an individual
user application
• When you create a new project, you can
select the type of project it will be, which
specifies how the project file is compiled
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Visual Basic Projects
Figure 6-3:
Visual Basic
project types
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The Visual Basic
Development Environment
• Integrated development environment (IDE)
– Environment for developing programs
Figure 6-4:
VB IDE
components
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The Visual Basic
Development Environment
• Main IDE components include:
– The toolbar provides quick access to menu bar
commands for opening
– The Object window shows the form and the
position of the controls on the form
– The toolbox contains icons that are used to
create form controls
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The Visual Basic
Development Environment
• Main IDE components include (cont.)
– The Project Explorer displays a hierarchical list of
the components of the current project
– The Properties window is used to assign and display
the properties of the object that is currently selected in
the Form window
• Docking
– Allows the borders of windows to be attached, or
docked, to other windows
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Creating a Visual Basic
Database Application
• Data control
– Form control that is attached to a database table
– Used to sequentially step through the record to
view the items
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Creating a Visual Basic
Database Application
Figure 6-8:
Clearwater Traders
Inventory
Maintenance
application
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Modifying Form Properties
• The properties of a VB object specify the
object’s appearance and behavior
• Name property
– Determines how objects are internally
identified within the project
– Must begin with a letter and can contain
characters, numbers, or underscores
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Modifying Form Properties
Table 6-1: VB object name prefixes
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Modifying Form Properties
• To follow accepted Windows application design
guidelines, you should always modify the
following form properties:
– Border Style, which determines whether the user can
resize the form
– Caption,which is the form description that is displayed
in the form’s title bar
– MaxButton, which allows the user to maximize the
form so that it is displayed full-screen
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Modifying Form Properties
• To follow accepted Windows application
design guidelines, you should always modify
the following form properties (cont.):
– MinButton, which allows the user to minimize
the form
– StartUpPosition, which determines where the
form is displayed on the screen when the
application is running
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Saving Visual Basic Projects
• A VB project is saved in a file with a .vbp
extension
• Forms are saved in files with an .frm
extension
• When you create a new project, it is very
important to always save the project (.vbp)
file and the form (.frm) file in the same
folder in your file system
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Using Visual Basic with a
Database
• ODBC driver
– Low-level program that translates messages
from an application into the syntax expected by
a specific database
– Each different type a database requires a
different ODBC driver
– Always runs on the client workstation
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Using Visual Basic with a
Database
• Programs written in program development
languages and applications that access databases,
need to communicate with ODBC drivers
• To simplify this communication, Microsoft has
developed a variety of different data access
technologies: Data Access Objects (DAO),
Remote Data Objects (RDO), and ActiveX
Data Objects (ADO)
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Using Visual Basic with a
Database
• DAO
– Available in most applications that support database
connectivity, but cannot support action queries that
change content in some databases
• RDO
– Full-featured, but only available in Microsoft’s high-end
enterprise-level programming environments
• ADO
– Full-featured, is available in most Microsoft
environments, and supports most types of queries
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Using Visual Basic with a
Database
Figure 6-12: Microsoft data access architecture using ODBC
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Using Visual Basic with a
Database
Figure 6-13: Microsoft data access architecture using ADO and OLE DB
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Creating an ActiveX
Data Control
• ActiveX data control
– A control that is displayed on a form
– Different from an ordinary form control
because it is associated with a recordset
• A specific set of database records based on a SQL
query
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Creating an ActiveX
Data Control
Figure 6-14: ActiveX data control
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Creating an ActiveX
Data Control
• To create an ADO data control, you must add a
type library to your project
• A type library is a library of code that has
programs, such as additional controls, that you
can add to VB IDE and then use in your
project
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Using Program Code
to Process Data
• With a programmatic data connection:
– All of the commands to create the connections and
execute SQL commands are specified in a VB
standard module
– User does not have to interact with a visible data
control to perform database operations
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Using Program Code
to Process Data
Figure 6-17:
Creating a data
connection
programmatically
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Code in Visual Basic Programs
• A VB project consists of forms and standard
code modules
• Every form and every code module has a
section called the General Declarations
section
– Contains declarations for variables, and the code
for functions and procedures that are used in the
form or code module
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Variables in Visual Basic
Programs
• Visual Basic code has variables and data
types just like other programming languages
• It is a good programming practice to always
declare variables before using them
• VB does not require you to declare
variables, but allows you to assign a value
to a variable without declaring it first. This
can lead to errors
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Variables in Visual Basic
Programs
• Declaration keyword that is used to declare a
variable depends on the desired scope of the
variable
• Scope
– Specifies how long the variable exists in memory
– Specifies what program components can assign and
access the variable value
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Variables in Visual Basic
Programs
• Variable declaration keywords are used as
follows:
– The Public keyword is used to declare global
variables
– These are variables that are visible to all forms
and modules within a project
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Variables in Visual Basic
Programs
• Variable declaration keywords are used as
follows (cont.):
– The Private keyword is used to declare formlevel and standard module-level variables
– These are variables that are visible only to
procedures and functions written within the
form or standard module where the variable is
declared
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Variables in Visual Basic
Programs
• Variable declaration keywords are used as
follows (cont.):
– The Dim keyword is used to declare local
variables
– These are variables that are visible in the
function or procedure where they are declared
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Variables in Visual Basic
Programs
• Variable declaration keywords are used as
follows (cont.):
– The Static keyword is used to declare local
variables whose values are only visible within
the procedure where they are declared, but
whose values still exist and can be accessed
after the procedure is exited
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Variables in Visual Basic
Programs
• The Variant data type can store any type of data
Table 6-2: Visual Basic data types
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Visual Basic Objects and
Collections
• In object-oriented programming languages, an
object is an item that has a specific structure
and behavior
• Methods
– Procedures that perform an operation on an object
• Collection
– Contains a set of related objects
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Running Programs in the
Visual Basic IDE
• Source code
– The program code that you write
• Interpreted
– Means that the code is translated to machine language
and executed one line at a time
• Compiled
– Means that all of the code is translated into machine
language, and the machine-language version is then
stored as an executable file
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Message Boxes
• A message box provides information to user
regarding status of program or current operation
Figure 6-23:
Message box
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Message Boxes
• A return value is an integer value that corresponds to the
button the user clicks in the response to the message box
• A prompt is a text string that specifies the message
displayed in the message box
Table 6-3: Message box return values
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Message Boxes
• Buttons
– Defines the buttons that are displayed in the
message box
– Commonly used values include:
•
•
•
•
vbOKOnly
vbOKCancel
vbYesNo
vbYesNoCancel
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Message Boxes
• Title is a text string that defines the text that
is displayed in the message box title bar
Table 6-4: Predefined message box definitions
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Using a DataGrid Control
• To display database records on a Visual
Basic form, you use a DataGrid
– Always associated with an ADO control, which
specifies the database connection and the SQL
query that returns the records that are displayed
in the grid
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Using a DataGrid Control
Figure 6-29: Inventory form
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Displaying and Hiding Forms
in a Project
• In Visual Basic, a form can be displayed as
modal or modeless
– Modeless
• User can interact with other project forms while the
form is displayed
– Modal
• User can interact with only the modal form, and
cannot interact with any other project forms until the
modal form is unloaded
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Displaying Visual Basic
Programs Using Web Pages
• Visual Basic projects can be created to
make standard executable files
• Also can be created using different ActiveX
options to make programs that can be
installed and/or run by clicking a hyperlink
on a Web page
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ActiveX Options Supported by
Visual Basic
• Active documents
– Have both a visual interface and code to process user
inputs and actions
• Active programs
– Provide processing for other Web programs, but do not
have a visual interface component
• Active controls
– Used to create custom controls that can be used in other
Web-based programming projects
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Creating an ActiveX Document
• User document
– Container object in an ActiveX document
– Similar to a form in the sense that it can contain
controls and code, and has events similar to
those in a form
• A user document must be associated with, or
sited on, an external application, which is
called a container
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Creating an Installation Package
for Your ActiveX Document
• Installation package - has the files needed to
install an application on a user’s
workstation
• Visual Basic provides a program called the
Package and Development Wizard that
leads developers through the steps needed
to create an installation package
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Displaying an ActiveX
Document using a Hyperlink
• When creating a Internet package using Package and
Development Wizard, the Wizard creates an HTML file
containing the command for the hyperlink that references
the ActiveX document
Figure 6-34: Link to ActiveX document file in HTML file created by
Package and Development Wizard
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ActiveX Documents and
Security Considerations
• One approach to controlling and screening
ActiveX programs is the use of verification
certificates
– These certify that software is from a
trustworthy source
• With verification certificates, users can be
confident that the certified software will not
harm their workstations
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Chapter Summary
• Visual Basic is a development language and used
to create Windows-based applications
• A VB project can have forms and code modules
• Visual Basic has an integrated development
environment (IDE) with multiple windows for
displaying and modifying project components
• Visual Basic forms and controls have properties,
which determine how the forms and controls look
and function
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Chapter Summary
• An Open Database Connectivity (ODBC) driver is
a program that allows an application to interact
with a database
• A DataGrid is used to display multiple database
records in a matrix format
• You can create a VB project that is an ActiveX
document, which has both visual components and
code, and can be displayed as a Web page using
the Microsoft Internet Explorer browser