VBA – Visual Basic for Applications

Week 20 - Tutorial

Objectives

At the close of this tutorial you should understand

Objects, Properties, Methods and Events

Event driven programming Basic VBA programming syntax Functions and Procedures

What is VBA VBA is a programming language It can be used in all major

Microsoft Office Applications VBA allows developers to create

their own functions and procedures to enhance bespoke databases or spreadsheets

It is more powerful and flexible than Access macros

Objects Properties Methods and Events

Before we can create any VB code we must understand Objects Properties, Methods and Events

Objects – can be anything in your database such as a form, textbox, combo box – the database is also an object. Other applications such as Excel are also objects

Properties

Objects can have Properties that describe their characteristics

A Form has a Caption property, a textbox has a Font property

We can set the fonts attributes by setting some of the textboxes properties such as Bold or Italic

Methods

Object also have Methods, which allow actions to be done to the objects

A Recordset object has an AddNew method that allows the addition of a new record – it also has MoveFirst, Delete, Insert etc.

Events

Closely related to methods are Events

VBA is an Event driven programming language

A Event is a specific action that occurs on or with an Object

VBA is totally dependent on events being initiated or occurring

Events cont. The Click event of a button is

probably the most commonly initiated event

When you click a command button on a form, the code within the click event is executed

All controls that are placed on a form have events – the form itself has its own events

Modules All the code for a VBA program is

contained in Modules VBA has Class and Standard Modules Each Form and Report has its own Class

module that contains code that is specific to that form or report

A standard module contains generic code that is not specific to any particular object and can be deployed anywhere within a program

Viewing a Form Module

To view a Form module open the form in Design View and click on the code icon on the toolbar

The Form Class Module Code Window

The code module is displayed

Form Class Module

If we click on the ‘General’ dropdown list we can see a list of Objects (controls) that have been placed on the form. It also lists the Form itself

Form Class Module

If we select ‘Form’ from the list, the ‘Declarations’ dropdown list displays ‘Load’ – this refers to the Form Load Event

Form Class Module If we click on the declaration drop down

list we can view all the other Events available to the form

When you select an Event, a code template is created in the code window – this is where we add the code for that Event

Code goes in here

Coding an Event To access both the properties and the

controls on the form we use the reserved word Me

This refers to the form itself To access the properties and controls

we use the dot (.) notation For example, to access the Form’s

Caption property we would useMe.Caption

Coding an Event To set the Caption property we can enter a

name in speech marks and click save, and no matter what name exists in the form name property, the Load Event code will over-ride it to display the name defined in the procedure

Procedures and Functions Apart from Event procedures developers can

write their own procedures and functions or more correctly Sub Procedures and Function Procedures

Sub Procedures perform actions and can be run directly or in response to an event

Function Procedures return a single value of any data type i.e. String, Integer, Date…

Modifying Existing Event Procedures Access can satisfy most user requirements,

however, by providing your own VBA code you can create individual bespoke Access database applications

The code that Access provides for a control’s event procedures can be rewritten to suit your own application and confirmation and error messages can be overridden and replaced by more suitable messages

Modifying Existing Event Procedures When you create an input form using

the wizard, Access does not provide a Delete option, only record navigation and add new record options

Navigation buttons

Add New button

Adding Delete Button To add a delete option place a command

button on the form and using the wizard set the button to Delete Record

When the button is clicked an internally generated message is displayed – if the user clicks ‘No’ then another message is displayed

Each message has the Microsoft Office Access caption

Customising Messages To disable Accesses error messages select

Tools->Options, select the edit/Find tab, uncheck Record changes and click Apply

Record Changes

Customising Messages We now need to edit the Access

generated code of the Delete button In Design mode click on the delete

button to display the properties window

Go to the ‘Click’ Event and click on the ellipses – this will take you to the click event procedure code template – see next slide

Customising Messages The code prefixed with DoCmd is the

code that deletes the record – all the rest is Access generated error trapping, which we want to keep

Message Boxes To display messages to the end user

when the program is running VBA uses message boxes (MsgBox)

They can be deployed in various ways depending on the requirements

If they are to display only messages that inform users of a particular state or condition then the format can be either of the following – see next slide

Message Boxes

MsgBox”Record Saved” – which will return only the text in an OK only message box with the Access caption

Message Boxes

MsgBox "Record Saved", vbInformation – which displays the same as previously shown but with an exclamation mark

Message Boxes MsgBox "Record Saved", vbInformation, "Bilbos Products”

– As previous but with user defined caption

Message Boxes We can also get the message boxes to

respond to user input i.e. Delete Record Yes/No/Cancel

To do this we must use the MsgBox as a function i.e. return a single value

When a message box uses the vbYesNoCancel function it returns an integer value dependant on whether the user has clicked Yes, No or Cancel

Message Boxes Yes = 6 No = 7 Cancel = 2 If we give this value to a variable we

can then evaluate the value using an ‘If’ statement in the code and display other messages or performing other tasks dependant on the users choice

Evaluating Message Boxes The format for such a message is:

Evaluating Message Boxes We declare an integer variable to contain

the response using the ‘Dim’ VB keyword The message box parameters must be

encapsulated in parentheses It is then passed to the variable

Dim response As Integer

response = MsgBox("Delete Record?", vbYesNoCancel + vbQuestion, "Bilbos Products")

Evaluating Message Boxes

The variable is then evaluated using the If statement – notice the other message boxes used to inform the user whether the record has been deleted or not

If response = 6 Then DoCmd.DoMenuItem acFormBar, acEditMenu, 8, , acMenuVer70 DoCmd.DoMenuItem acFormBar, acEditMenu, 6, , acMenuVer70 MsgBox "Record Deleted", vbInformation + vbOKOnly, "Bilbos Products" Else MsgBox "Record Not Deleted", vbInformation + vbOKOnly, "Bilbos Products" End If

Evaluating Message Boxes

You can also use the vbYes function in place of the number i.e. 6, to make the code more readable

For more information on message boxes read pages 12 – 14 of the VBA trainer

Custom Event Procedures If a user accidentally changes data

in a form and moves to the next record the data is saved

We can prevent this by adding code to one of the many form events available

The BeforeUpdate event is invoked if any changes have been made to the data

BeforeUpdate If we add the following code to the event

and the user changes any data, clicks any of navigation buttons and then selects Yes, the data is saved otherwise the save is undone

Private Sub Form_BeforeUpdate(Cancel As Integer) Dim response As Integer response = MsgBox("Save Details", vbYesNo, "Save") If response = vbNo Then Me.Undo Cancel = False End IfEnd Sub

BeforeUpdate

If we change Cancel to True, then the current record remains displayed when the user selects No

If we add a Save button to the form then the BeforeUpdate event is called whenever data is changed and the Save button is clicked – see next slide

BeforeUpdate

Inbuilt Functions VBA has many inbuilt functions i.e.

IsNumeric, IsDate etc that can be used by the developer when validating user entry

For example, if we had a textbox named txtPurchaseDate we could trap any erroneous input by the user by coding an If statement in an event i.e.

If IsDate(txtPurchaseDate) then… The IsDate function is a Boolean function

that returns either True or False

User Defined Functions We can create our own functions and

place them in a Standard Module i.e. a module that is not tied to any form or report. They contain generic code to be used anywhere in the program

To add a standard module to the program click Insert->Module

User Defined Functions Assuming that the discount in the form below was

calculated from the purchase date and date paid i.e. paid before 30 days then 20% discount – 30-60 days 10% discount > 60 days no discount, we could code the calculation in the BeforeUpdate event

User Defined Functions However, we may need this calculation

elsewhere in the program so a separate calculation function in the module would be better – to do this, click on the code icon and in the project explorer, double click the Module icon

Project Explorer

Module Icon

User Defined Functions To add a new function template to the

module select Insert->Procedure Give the function a name. Set the Type as Function Set the Scope as Public –

we need to use this in more than one place

The code below uses the DateDiff inbuilt function that has 3 parameters and returns, in this instance, an integer value based on the difference in days between the 2nd two parameters given as parameters to the function

The getDiscount function returns a Single value

Given Parameters Return Value

User Defined Functions

User Defined Functions The function is useless unless it is

called from within an event in this case the BeforeUpdate event

Private Sub Form_BeforeUpdate(Cancel As Integer)Dim response As Integer response = MsgBox("Save Details", vbYesNo, "Save")If response = vbNo Then Me.Undo Cancel = TrueElse Me!txtDiscount = Null If Not Me!datePaid Then Me!txtDiscount = getDiscount(datePaid) End IfEnd IfEnd Sub

User Defined Functions We could also place the code in the

AfterUpate event of the datePaid text box so that the txtDiscount is calculated when the datePaid textbox loses the focus

Private Sub datePaid_AfterUpdate() Me!txtDiscount = Null If Not Me!datePaied Then Me!txtDiscount = getDiscount(datePaid) End IfEnd Sub

User Defined Sub Procedures

However, we are repeating code, which we want to avoid

To do this we select the Form Module an create a procedure by selecting Insert->Procedure

Make the procedure privateas it is only going to be used on this form

Select Private

User Defined Sub Procedures

Add the following code

Private Sub calculateDiscount()Me!txtDiscount = NullIf Not Me!datePaid Then Me!txtDiscount = getDiscount(PurchaseDate, datePaid) End IfEnd Sub

User Defined Sub Procedures Call the code from within each event

Private Sub Form_BeforeUpdate(Cancel As Integer)Dim response As Integer response = MsgBox("Save Details", vbYesNo, "Save") If response = vbNo Then Me.Undo Cancel = TrueElse Call calculateDiscountEnd IfEnd Sub

Private Sub datePaid_AfterUpdate() Call calculateDiscountEnd Sub

User Defined Sub Procedures See how much neater the code is – this is

called code re-use However, there is another calculation to

be done on the form –the total price based on the number of products, the product price and the discount i.e.

total=productPrice*noOfProducts*discount

Finishing it off We need another function in our

Standard Module – getTotalPrice that returns a currency value

Public Function getTotalPrice(discount As Single, price As Currency, noProducts) As CurrencyDim total As CurrencyIf Not discount And price <> 0 And noProducts <> 0 Then total = (discount * (price * noProducts)) + price * noProductsElseIf price <> 0 And noProducts <> 0 Then total = price * noProductsElse total = 0End IfgetTotalPrice = totalEnd Function

Finishing it off If we add the new function to our calculateDiscount

procedure and change the name of the procedure to a more suitable name i.e. calculatePrice, we can call this procedure from other events

Task – try adding a similar procedure to the AfterUpdate event of some of the input texboxes in a program of your own

Private Sub calculatePrice()Me!txtDiscount = NullMe!txtTotal = Null If Not Me!datePaid Then Me!txtDiscount = getDiscount(PurchaseDate, datePaid) Me!txtTotal = Format((getTotalPrice(Me!txtDiscount, Me!ProductPrice, Me!noOfProducts)), "Currency") End IfEnd Sub

Finishing it off This is my final code for the form on the right

Private Sub datePayed_AfterUpdate() Call calculatePriceEnd Sub

Private Sub Form_AfterUpdate() Call calculatePriceEnd Sub

Private Sub Form_BeforeUpdate(Cancel As Integer)Dim response As Integer response = MsgBox("Save Details", vbYesNo, "Save") If response = vbNo Then Me.Undo Cancel = TrueElse Call calculatePriceEnd IfEnd Sub

Private Sub Form_Current() Call calculatePriceEnd Sub

Private Sub noOfProducts_AfterUpdate() Call calculatePriceEnd Sub

Summary

In this tutorial we have covered: Objects, Methods, Properties and

Events Modules – Class and Standard Modifying Event Procedures Adding user defined messages Adding User Defined Function Adding User Defined Sub Procedures

To cover VBA in any depth would require a whole module – at least

This tutorial has hopefully given you some ideas in how to customise Access programs

For a more detailed coverage see references

Summary cont.

References “Getting Started with MS VB for

Applications (VBA) “ - Available from your lecturer or from one of it’s creators, Mary Spence

“Further Uses of MS VBA” – same authors as above

Any ‘Good’ book – especially Microsoft publications