Project 4

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Project 4
Menus, Data Controls, Common Dialogs, and
General Procedures

Visual Basic Capabilities

Visual Basic can be used to build applications that display, edit and update information from databases created by the following DBMS products: Microsoft Access, dBase, FoxPro, and Paradox.

Project 4 Outline

Project 4 provides exposure to accessing a database by building an application that displays information from a World Geography database created with Access
World Geography database is included on Student Diskette.
Project describes only how to display information. VB can be used to create applications that query, add, change, and delete records are covered in later project.

Common Database Terms

field - single item of data (characteristic or attribute )
(graphic image - country flag)
record - group of fields (person or item)
table - group of related records (file)
database -collection of related facts organized in a systematic manner
DBMS - database management system - collection of software that manipulates a database

Geography Database Viewer

Geography Database Viewer does not have any visible controls
reason all interaction occurs by using menus or the Data Control
Select menu - Next, Previous, First and Last
File menu - Exit
Options Menu
- View menu Name, Capital, Government
- Font menu Font common dialog box
Shortcut menu can also be used (Options)

Getting Started

The database file WORLD.MDB and the icon named Earth.ico used in this project is found on the Student Disk.
These files should be copied to another disk that will be used later to save the completed application

Creating the Interface

Size and Location of Form determined
Viewer form contains - one image control, 6 label controls, one data control and one common dialog control

Note: common dialog control is not visible at run-time

Adding Label Control Array

Control array - is made up of a group of controls of the same type that share a common control name and a common set of event procedures
Array index - a unique index number is assigned by Visual Basic to each element of the array starting at 0

Control Array Continued

All items in control array must have the same Name property setting
All other property settings apply only to the individual control

Example: Label1(0) can have a caption and other property settings different from Label1(1)

Arrays make it easier to change a property of a group of controls to a common value during run-time.

Label Array Properties

FontSize can be changed through a simple code structure
Six labels have AutoSize property set to True and have the same BackStyle property (Transparent, Opaque)
- These two properties will be set for the first control during the interface building step, rather than during the set properties step, so that these properties can be copied to the other controls

Adding Common Dialog Control

Common dialog control is used in applications to display one of five common dialog boxes at run-time
Open, Save As, Print, Color, and Font
Common dialog control invisible (run-time)
Common dialog control is an ActiveX control and must be added to the Toolbox before you can use it in your application

Adding Data Control

data control used in Visual Basic applications to provide the necessary links to a database file

Note: A form can contain more than one data control, and generally one data control exists for each database table accessed by the application

data control has four record selection buttons used during run-time to move between records

Geography Database Viewer
Data Control

Geography database Viewer application contains a data control to link to the World database. (WORLD.MDB)
Record selection is controlled through the data control or the Select menu
Code will be written that causes the Select menu commands to trigger data control events (data control needed by the menu)

Creating Menus

Menu Design Window - Visual Basic's tool used to create menus at design-time
Access keys - allow you to open a menu at run-time by pressing the ALT key and a letter. (Hot-keys) (& used at design-time)

Note: When a menu is open, you press only the access key of a command (not the ALT key.)
Example: Exit (press only the x key)

Menu Concepts

separator bar - horizontal line used to visually group related commands in a menu
- added to menu at design time by typing a hyphen (-) in the Caption text box
submenu - branches off another menu to present an additional set of commands in a separate grouping
Visual Basic can have up to four levels of submenu

Setting Properties (steps)

Properties of form
Properties of image control
Caption property of the label controls
Properties of the CommonDialog control
Properties of the data control
Properties of the data-aware controls

Setting Properties of Form

Name of the form is set
Form is given a Caption to appear in the title bar
Form's BackColor is set to match the BackColor of the label controls
BorderStyle property (1-Fixed Single)
MinButton property set to True
Icon specified to represent the form when it is minimized

CommonDialog Control Properties

Flags property used to set dialog box options
- Flags value = 1
  (Font dialog box lists only screen fonts supported by system)
In Visual Basic, default for FontName property is determined by the system.
Fonts available with VB vary depending on your system configuration. For this reason, when Font dialog box displays, a preselected Font does not exist.
Must set this FontName property at design time or with code at run time

Data Control Properties

Caption property - of Data control is text that displays between control's next and previous record buttons
Align property - determines whether control can be located anywhere on form or whether it is sized automatically to fit the form's width and displayed at the top, left, right, or bottom of the form

Setting Properties of Data Control

DatabaseName property - used to supply the file name of the database to which the data control is linked
Record Source property - used to specify the table name in the database to which the data control is linked
Connect property - used to specify the type of database (Access, FoxPro, dBase etc.) Note: not necessary to set connect property when Microsoft Access used

Setting Properties
Data-Aware controls

data-aware - controls within Visual Basic that can be linked to information in a database
data-aware controls are check boxes, images, labels, picture boxes, and text boxes.

Setting Properties
Data-Aware controls

to use these controls to access a database, the controls must be bound to a data control on the form
In multiform application, the bound control and data control to which it is bound must be on the same form
Data-aware controls are bound to a data control by setting their DataSource and DataField properties

Setting Properties
Data-Aware controls

DataSource property - of a control specifies the name of the data control to which it is bound
DataField property of a bound control specifies the name of a field in the database to which the control is linked
Not necessary to change caption property of bound labels to blank since captions will take on field values of 1st record of table

Writing Code (table 4-2 VB 4.38)

Geography Database Viewer code tasks

frmGeoView_MouseUp subroutine
mnuExit_Click subroutine
Select menu subroutines
- mnuNext, mnuPrev, mnuFirst, mnuLast
mnuFont_Click subroutine
mnuView_Click submenu subroutines
- mnuName, mnuCapital, mnuGovt

QueryUnload Event

Before a form is unloaded, the Form_QueryUnload event procedure occurs, followed by the Form_Unload event procedure
Event typically used to make sure that before an application closes, no unfinished tasks remain
- (put code in this event reminding users to save data)

Select Menu Subroutines

One event is associated with each of the four commands in the Select menu: mnuNext_Click, mnuPrev_Click, mnuFirst_Click, and mnuLast_Click
These actions are the same as if the data control was clicked on the appropriate record selection button
Actions in code with methods MoveNext, MovePrevious, MoveFirst, and MoveLast

Code statement form

DataControlName.Recordset.MoveMethod

Example: Data1.Recordset.MoveNext

EOF property - End Of File occurs when on last record and MoveNext method is used (property changes from false to true)
BOF property - Beginning Of File occurs when on 1st record and MovePrevious method is used (property changes from false to true)

Coding EOF statement

Data1.Recordset.MoveNext
If Data1.Recordset.EOF = True Then Data1.Recordset.MoveFirst
Note: If the MoveNext command causes the current record to move past the last record, then the first record in the database becomes the current record

MouseUp Event

MouseDown or MouseUp event used to specify actions that will occur when a given mouse button is pressed or released
- (enable to distinguish among left, right, and middle mouse buttons) (2=right)

If Button = 2 Then PopupMenu mnuOptions

Options pop-up menu to display when user right-clicks the form
can specify position of pop-up menu, use default location (current location mouse pointer)

Using Font Property

Font properties - selected font properties becomes the values of common dialog control's font properties when the Font dialog box is closed
Set Font properties of the 6 labels to equal Font properties of common dialog control

Code :

Label1.FontSize = CommonDialog1.FontSize

For...Next statement (loop)

For counter = start To end (header part)

[statements] (repeated)

Next (terminator part)

counter - numeric variable (loop counter)
start - initial value of counter
end - final value for counter
Next - Ends a For...Next loop; causes 1 to be added to counter

With Statement

With statement used to execute a series of statements on a single object or control

Syntax:
With object

[statements]

End With

Object - is the name of the object or control
[statements] - group of code statements that operate on object

Potential Problem

Possible to increase font size where captions extend beyond form's right border

Solution: - write code statements that adjust form's size (Height and Width) and controls' locations (Top and Left)

In GeoView application code statements adjust the Width of the form and center the Image control right to left

For...Next and Arrays

mnuFont_Click subroutine uses For...Next loop to set the Font properties of the 6 labels using With statement

Coding:
For X = 0 To 5

With Label1(X)

.FontName = CommonDialog1.FontName (etc)

End With

Next

General Procedures

General procedures include subroutines, also called Sub procedures, and functions
Function procedures and Sub procedures are separate procedures that can take arguments, perform a series of statements, and change the value of their arguments
- Sub procedure cannot be used in an expression

General Procedures

Advantage: - when multiple events execute similar code, it is more efficient to put code in a general procedure and then activate the general procedure from the appropriate events

Activate or call a Sub procedure using the procedure name followed by the argument list

Example of call: - ToggleView mnuName, 1

General Procedures

General procedures may have none or one or more arguments (multiple arguments are separated by commas)
After the general procedure is completed, program control returns to the code statement following the one that called the general procedure

Check Marks in Menus

Checked property of menu can be set at design-time by clicking the Checked box in the Menu Design Window (causes check marks to appear before menu item when program runs)
Code can be used to add or remove checks during run-time by setting menu control's Checked property to True or False

Code: mnuFlagshow.Checked = True

Project 4
Menus, Data Controls, Common Dialogs, and
General Procedures
END

Program Creating a Database Viewer Application Requirements

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