WORKING WITH FILES,
MENUS AND DATABASES
IN VISUAL BASIC
BY
V. V. SUBRAHMANYAM
Working with files

Visual Basic File System Controls
DriveList Box
DirList Box
FileList Box
DriveList Box control
Is a drop down list box
 Displays the list of drives on your
computer
 The change is recorded in Drive
property of the DriveList Box

DirList Box Control
It is a Drop down list box
 Displays the hierarchical list of
Directories in the current drive

FileList Box
It is a Drop down list box
 Displays all files in the current directory
or folder and also allows the user to set
up search criteria for files

Advantages of file system
controls

These three controls used together can
create an elegant interface that will
allow the user to locate a file on his
computer
Private Sub Dir1_Change()
File1.Path = Dir1.Path
End Sub
Private Sub Drive1_Change()
Dir1.Path = Drive1.Drive
End Sub
Private Sub Text1_Change()
File1.Pattern = Text1.Text
End Sub
File functions
ChDrive - Changes the current logged
drive
 ChDir
- Changes the default
directory
 MkDir
- Creates a new directory
 RmDir - Deletes a directory
 Name
- Renames a file

Contd…
Kill
- Deletes a file
 FileCopy - Copies a file from src to des
 FileDateTime – Returns the date and
time when the file was modified
 GetAttr
- Returns the attributes of a
file as an integer value
 SetAttr
- Sets the attributes of a file

Menus
Contains a no. of options, logically
organized and easily accessible.
 In VB Menus can be created using the
Menu Editor
 Menu is tied to a form.

Menu Conventions
Keep menu captions short and simple
 Follow the Windows conventions while
naming and ordering the menu items
 Keep the list of menu items short
 Use separators to logically group menu
options
 Provide necessary keyboard shortcuts

Multiple Document Interface
(MDI)

MDI was designed for applications
which need to show more than one
document(multiple documents) at the
same time, with each document
displayed in its own window.
Why MDI forms?
MDI form acts like a container for the
other forms in the application
 Most of the control buttons and code for
the various forms can be shared
 Reduces the no. of controls

MDI Application
An application can have only one
MDI form
 One or more MDI Child Form(s)
 Optionally independent forms and
modules

Data Base
It is a collection of records stored in
tables.
 Information is stored in tabular form and
is called a table.
Columns  Fields
Rows
 Records
 The collection of the tables is called as
database and are stored in a file.

Three categories of databases

Visual Basic recognizes 3 categories of
databases
Visual basic database
External databases
ODBC databases
Creating a table

You can create your own tables using
– DAO(Data Access Objects)
– Microsoft Access and others
– Visual Data Manager
Visual Data Manager
Visual Data manager makes the job
of table creation and modification very
simple.
 This can work with MS-Access,
Dbase, Paradox and text files also.

Data Control
Establishes a connection to a database
 Returns a set of records from the
database
 Enables you to move from record to
record
 Enables you to display and manipulate
data from the records in bound controls

Properties to be set to Data
control

Two properties to be set at runtime or
design time are:
DatabaseName: Specifies the name of
the database that must be opened
RecordSource: Specifies the name of
the table(s) of the database from which
the data has to be extracted
Data-Aware Control

It is the control that provides access to a
specific field in a database through a
data control.This can be bound to a
data control through its data source and
data field properties.
DBlist, Dbcombo and Dbgrid

These controls are all capable of
managing sets of records when bound
to a Data Control. All of these controls
permit several records to be displayed
or to be manipulated at a time.
`Object Linking and
Embedding(OLE)

To create an application that can
display data from many different
applications and enables the user to
edit that data from with in the
application in which it was created.
OLE DB
It is defined as a new low-level interface
that is part of the Universal Data Access
platform.
 It is general purpose set of interfaces
designed to let developers build data
access tools as components using the
COM.

Additional Controls
Sstab control

Provides an easy way of presenting
several dialogs or screens of
information on a single form, using the
same interface seen in many
commercial Windows applications.
ImageList control

This control acts like a repository of
images for the other controls
MSFlexGrid control

This displays and operates on data in a
table form
Toolbar Control

This is used to create a toolbar for the
application, just like Toolbars for
applications like Word or Excel or
others.
Statusbar Control

This control holds up to a maximum of
sixteen panels or frames each of these
panel given different types of
information like time, microhelp, status
of a key etc..
Treeview Control

To display the data as a hierarchy. It
displays the drives, directories,
subdirectories and files in the form of a
hierarchy.
ActiveX Data object

This enables the client applications to
access and manipulate data in a
database serer through any of the OLE
DB providers.
Benefits of ADO
Ease of use
 High speed
 Low memory overheads
 Small disk footprint

ADO support

ADO support key features for building
client/server and Web-based
applications.
BUG

The error or the problem occurred in the
system is called as a bug
Debugging

The process of finding out and removing
the error is called debugging.
Types of Bugs
Errors of syntax
 Logical errors
 Runtime Errors

Debugging Methods
The Message box
 Debug.print
 Debug Toolbar
 Error Handler

Message Box

To display the state of values that have
been assigned to a variable
Dim I as integer
For I = 1 to 20 step 4
MsgBox I
----Next I
Debug.print

The debug object will send the output to
the immediate window.
Dim I as integer
For I = 1 to 20 Step 4
Debug.print I
Next I
Debug Toolbar
To begin debugging, Debug Toolbar is
required.
 To bring up, right click the toolbar and
select Debug from the pop-up menu

Error handler

It is a routine that traps errors and
directs the user or the program to
perform a certain task to overcome the
error.