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INTRODUCTION TO VISUAL BASIC

The Integrated Development Environment

One of the most significant changes in Visual Basic 6.0 is the Integrated Development Environment (IDE). IDE is a term commonly used in the programming world to describe the interface and environment that we use to create our applications. It is called integrated because we can access virtually all of the development tools that we need from one screen called an interface. The IDE is also commonly referred to as the design environment, or the program.

Tha Visual Basic IDE is made up of a number of components
Menu Bar
Tool Bar
Project Explorer
Properties window
Form Layout Window
Toolbox
Form Designer
Object Browser

In previous versions of Visual Basic, the IDE was designed as a Single Document Interface (SDI). In a Single Document Interface, each window is a free-floating window that is contained within a main window and can move anywhere on the screen as long as Visual Basic is the current application. But, in Visual Basic 6.0, the IDE is in a Multiple Document Interface (MDI) format. In this format, the windows associated with the project will stay within a single container known as the parent. Code and form-based windows will stay within the main container form.

Figure 1 The Visual Basic startup dialog box



Menu Bar

This Menu Bar displays the commands that are required to build an application. The main menu items have sub menu items that can be chosen when needed. The toolbars in the menu bar provide quick access to the commonly used commands and a button in the toolbar is clicked once to carry out the action represented by it.
Toolbox

The Toolbox contains a set of controls that are used to place on a Form at design time thereby creating the user interface area. Additional controls can be included in the toolbox by using the Components menu item on the Project menu. A Toolbox is represented in figure 2 shown below.

Figure 2 Toolbox window with its controls available commonly.


Control Description
Pointer Provides a way to move and resize the controls form
PictureBox Displays icons/bitmaps and metafiles. It displays text or acts as a visual container for other controls.
TextBox Used to display message and enter text.
Frame Serves as a visual and functional container for controls
CommandButton Used to carry out the specified action when the user chooses it.
CheckBox Displays a True/False or Yes/No option.
OptionButton OptionButton control which is a part of an option group allows the user to select only one option even it displays mulitiple choices.
ListBox Displays a list of items from which a user can select one.
ComboBox Contains a Textbox and a List Box. This allows the user to select an item from the dropdown List Box, or to type in a selection in the Textbox.
HScrollBar and VScrollBar These controls allow the user to select a value within the specified range of values
Timer Executes the timer events at specified intervals of time
DriveListBox Displays the valid disk drives and allows the user to select one of them.
DirListBox Allows the user to select the directories and paths, which are displayed.
FileListBox Displays a set of files from which a user can select the desired one.
Shape Used to add shape (rectangle, square or circle) to a Form
Line Used to draw straight line to the Form
Image used to display images such as icons, bitmaps and metafiles. But less capability than the PictureBox
Data Enables the use to connect to an existing database and display information from it.
OLE Used to link or embed an object, display and manipulate data from other windows based applications.
Label Displays a text that the user cannot modify or interact with.

Project Explorer

Docked on the right side of the screen, just under the tollbar, is the Project Explorer window. The Project Explorer as shown in in figure servres as a quick reference to the various elements of a project namely form, classes and modules. All of the object that make up the application are packed in a project. A simple project will typically contain one form, which is a window that is designed as part of a program's interface. It is possible to develop any number of forms for use in a program, although a program may consist of a single form. In addition to forms, the Project Explorer window also lists code modules and classes.

Figure 3 Project Explorer

Properties Window

The Properties Window is docked under the Project Explorer window. The Properties Window exposes the various characteristics of selected objects. Each and every form in an application is considered an object. Now, each object in Visual Basic has characteristics such as color and size. Other characteristics affect not just the appearance of the object but the way it behaves too. All these characteristics of an object are called its properties. Thus, a form has properties and any controls placed on it will have propeties too. All of these properties are displayed in the Properties Window.
Object Browser

The Object Browser allows us to browse through the various properties, events and methods that are made available to us. It is accessed by selecting Object Browser from the View menu or pressing the key F2. The left column of the Object Browser lists the objects and classes that are available in the projects that are opened and the controls that have been referenced in them. It is possible for us to scroll through the list and select the object or class that we wish to inspect. After an object is picked up from the Classes list, we can see its members (properties, methods and events) in the right column.

A property is represented by a small icon that has a hand holding a piece of paper. Methods are denoted by little green blocks, while events are denoted by yellow lightning bolt icon.

Object naming conversions of controls (prefix)

Form -frm
Label-lbl
TextBox-txt
CommandButton-cmd
CheckBox -chk
OptionButton -opt
ComboBox -cbo
ListBox-lst
Frame-fme
PictureBox -pic
Image-img
Shape-shp
Line -lin
HScrollBar -hsb
VScrollBar -vsb


DATABASE CONNECTIVITY

A database is a collection of data that is related one to another to support a common application. For example Employee details - Name, Address, etc. Each of these collections of data continue a database.

Database accessing methods are as follows;

Jet Engine - Accessing Microsoft Access and Visual Basic databases.

ODBC (Open Database Connectivity) - Allow access to the client server databases on a network.

ISAM (Index Sequential Access Method) - Used to access flat databases such as dBase, FoxPro, ParaDox.
Bound Data Tools

• Most of the Visual Basic tools we’ve studied can be used as bound, or data-aware, tools (or controls). That means, certain tool properties can be tied to a particular database field. To use a bound control, one or more data controls must be on the form.

• Some bound data tools are:

Label - Can be used to provide display-only access to a specified text data field.

Text Box - Can be used to provide read/write access to a specified text data field. Probably, the most widely used data bound tool.

Check Box - Used to provide read/write access to a Boolean field.

Combo Box - Can be used to provide read/write access to a text data field.

List Box - Can be used to provide read/write access to a text data field.

Picture Box - Used to display a graphical image from a bitmap, icon, or metafile on your form. Provides read/write access to a image/binary data field.

Image Box - Used to display a graphical image from a bitmap, icon, or metafile on your form (uses fewer resources than a picture box). Provides read/write access to a image/binary data field.

• There are also three ‘custom’ data aware tools, the DataCombo (better than using the bound combo box), DataList (better than the bound list box), and DataGrid tools, we will look at later.

• Bound Tool Properties:

DataChanged - Indicates whether a value displayed in a bound control has changed.

DataField - Specifies the name of a field in the table pointed to by the respective data control.

DataSource - Specifies which data control the control is bound to.

If the data in a data-aware control is changed and then the user changes focus to another control or tool, the database will automatically be updated with the new data (assuming LockType is set to allow an update).

• To make using bound controls easy, follow these steps (in order listed) in placing the controls on a form:

Draw the bound control on the same form as the data control to which it will be bound.

Set the DataSource property. Click on the drop-down arrow to list the data controls on your form. Choose one.

Set the DataField property. Click on the drop-down arrow to list the fields associated with the selected data control records. Make your choice.

Set all other properties, as required.

By following these steps in order, we avoid potential data access errors.

• The relationships between the bound data control and the data control are:

ADO (ActiveX Data Object) data control



• The ADO (ActiveX Data Object) data control is the primary interface between a Visual Basic application and a database. It can be used without writing any code at all! Or, it can be a central part of a complex database management system. This icon may not appear in your Visual Basic toolbox. If it doesn’t, select Project from the main menu, then click Components. The Components window will appear. Select Microsoft ADO Data Control, then click OK. The control will be added to your toolbox.

• As mentioned in Review and Preview, previous versions of Visual Basic used another data control. That control is still included with Visual Basic 6.0 (for backward compatibility) and has as its icon:


• The data control (or tool) can access databases created by several other programs besides Visual Basic (or Microsoft Access). Some other formats supported include Btrieve, dBase, FoxPro, and Paradox databases.

• The data control can be used to perform the following tasks:

1. Connect to a database.

2. Open a specified database table.

3. Create a virtual table based on a database query.

4. Pass database fields to other Visual Basic tools, for display or editing. Such tools are bound tools (controls), or data aware.

5. Add new records or update a database.

6. Trap any errors that may occur while accessing data.

7. Close the database.

• Data Control Properties:

Align Determines where data control is displayed.

Caption Phrase displayed on the data control.

ConnectionString Contains the information used to establish a connection to a database.

LockType Indicates the type of locks placed on records during editing (default setting makes databases read-only).

Recordset A set of records defined by a data control’s ConnectionString and RecordSource properties. Run-time only.

RecordSource Determines the table (or virtual table) the data control is attached to.

• As a rule, you need one data control for every database table, or virtual table, you need access to. One row of a table is accessible to each data control at any one time. This is referred to as the current record.

• When a data control is placed on a form, it appears with the assigned caption and four arrow buttons:



The arrows are used to navigate through the table rows (records). As indicated, the buttons can be used to move to the beginning of the table, the end of the table, or from record to record.