CS130/230 Lecture 12

Advanced Forms and Visual Basic for Applications

Friday, January 23, 2004

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We are going to continue using the vending machine example to illustrate some more of Access’ properties.

Advanced Forms

Yesterday we created an advanced form that used data from two tables and listed the picture of the driver. Now we will look at combo boxes.

Combo Boxes

A Combo box is the control that has a drop down list of valid values.

We will now modify our form so that it contains a drop down list of the customer name. The end user can then use the combo box to directly jump to the details of a specific customer.

Problem

Open up the form from yesterday and add a combo box somewhere in the form. The combo box wizard should automatically appear. Use the wizard to link the combo box to the name field in the customer table.

Switch to form view and test out your combo box.

Question: Can you see any problems/limitations with the combo box as it now stands?

We can tackle some of these limitations directly by programming in Visual Basic.

Visual Basic for Applications

VBA is an event-driven programming language that can be used with Access.

Programs in visual basic consist of code, which is a collection of statements (commands), which are instructions that will cause actions to take place when the program is executed.

When working with Access, visual basic deals with events. Events are associated with user actions such as Click, DblClick, MouseDown, …

Variables: 255 characters beginning with a letter including letters, numbers, underscore (no spaces).

Assignment Statement: Factor = 1.05

Simple IF

If Customer_Type = “EDU” Then

Factor = 1.05

End If

Note: The If statement can also have an Else and ElseIf component.

Comments: these are notes to yourself that will be ignored by visual basic. You indicate a comment by placing an apostrophe just before the comment. Everything to the right of the apostrophe will now be a comment.

Functions : these are a group of statements that calculate and return a value.

Function Factor (Customer_Type)

‘ Determine factor base on Customer Type

If Customer_Type = “EDU” Then

Factor = 1.05

Else

Factor = 1

End If

End Function

Subroutines: these are a group of statements that do not return a value.

Public Sub ShowPromotion ()

txtPromoAmount.Visible = True

txtPromoFactor.Visible = True

cmdPromoQuery.Visible = True

End Sub

Module: a group of procedures

- Standard Module – procedures available anywhere in the DB

- Class Module – procedures available in a particular form or report

This was just a quick look at the basics in visual basic. The best way to really get a hang of it though is to use it directly.

Problem

We will use VB to modify the Add Record button so that as soon as we click on it, it will place an insertion point in the customer number box.

Question: What currently happens when we click on the Add Record button?

The first thing you need to do is go back to the Customer table and rename the field Customer Number to Customer_Number.

Question: Why do we need to do this?

Go back to the form, and in the design view, click on the text box and again rename Customer Number to Customer_Number. Once you have done this, click on the Build Event option on the toolbar.

VB opens up the code and goes directly to the subroutine for the text box. After the line that starts with DoCmd add

Customer_Number.setFocus

Close VB and test out the form.

Problem

The next thing that we are going to do is modify the combo box so that it

- matches the name of the current record

- sorts the names alphabetically

- is not included in the tabs

Another Example

Let us move onto another database example. For this one you will be working more independently but I’ll be there to help if needed.

Basically, every action we perform at the computer is an event that is sent to the Operating System. Events can be typing, mouse clicks, mouse moves, …

Let’s take a look at some Form events in Access:

- Open Event

- Load Event

- Resize Event

- UnLoad Event

- Close Event

Event Actions

Private Sub Form_Load()

MsgBox “Form Is Loaded"

End Sub

Problem

Load the DB VBAccess1.mdb and add the following code for the Open Event associated with the form frmAlgebraicOperators

Variable Declarations

In general, variables are declared using Dim

Private Sub NameIt()

Dim Name As String

Dim Value As Integer

Dim Found As Boolean

Dim Total As Single

End Sub

Other Possible Data Types

- Byte

- Long

- Double

- Currency

- Date

- Object

- Variant

Operators

- ‘ Comment ‘ This is a comment

- = Assignment txtName = txtFirstName

- “ String “hello there”

- & Concatenate “hi” & “there”

Problem

Continue using VBAccess1.mdb and do the following:

For each button, write the code that will calculate and display the Perimeter and Area for both the Square and Rectangle.

Problem

Insert another page into the VBAccess1.mdb database called Compute Wage. Allow the user the ability to input Hours Worked and Hourly Wage. Then call a function that returns the amount of money earned. Add a calculate button that when pressed calls your function and displays the proper value in the text area.

Function AmountEarned (dblHoursWorked As Double, dblHourlyWage As Double)

End Function

You will need to use an IF Then Statement

Looping

The general form for looping (doing something repeatedly) is:

Do While Condition

Statements

Loop

More Looping

Statements

Loop While Condition

Do Until Condition

Statements

Loop

Yet More Looping

For Counter = Start To End

Statements

For Each Element In Group

Statements

Next Element

Example

Sum = 0

For Counter = 1 To 10

Sum = Sum + Counter

Problem

Add another page called SumIt that allows the user the ability to enter a starting value and an ending value. Calculate and place the sum and average of the numbers, from the starting value to the ending value, in two separate text box areas in the form.