Access VBA ProgrammingAccess VBA Programmingfor Beginners for Beginners

- Class 2 -- Class 2 -byby

Patrick LasuPatrick Lasu

p_lasu@lycos.comp_lasu@lycos.com

Class 2 - OverviewClass 2 - Overview

Quick Review of Class 1Quick Review of Class 1 ConstantsConstants Why not using Variants all the timeWhy not using Variants all the time Option ExplicitOption Explicit Scope/Visibility and Lifetime of VariablesScope/Visibility and Lifetime of Variables

Quick Review of Class 1Quick Review of Class 1

VBAVBA– Visual Basic for ApplicationsVisual Basic for Applications

» Application = Access, Word, Excel, etc.Application = Access, Word, Excel, etc.

Event DrivenEvent Driven– User Event: Example - Clicking a ButtonUser Event: Example - Clicking a Button– Programming Event: Example - TimerProgramming Event: Example - Timer

At least 3 different ways to code the same At least 3 different ways to code the same tasktask

Quick Review of Class 1Quick Review of Class 1

Good Code – It worksGood Code – It works Bad Code – It does not workBad Code – It does not work Better Code – Make it “Short and Sweet”Better Code – Make it “Short and Sweet” Save often, use [CTRL]+[S]Save often, use [CTRL]+[S] Use the Help Files [F1]Use the Help Files [F1]

Quick Review of Class 1Quick Review of Class 1

A variable is a storage for a value that can A variable is a storage for a value that can change during code executionchange during code execution– Answering Yes or NoAnswering Yes or No

Quick Review of Class 1Quick Review of Class 1

There are several Data Types for Variables There are several Data Types for Variables and Constants for efficiencyand Constants for efficiency– String = Stores Text – “Patrick”, “123 Main St”String = Stores Text – “Patrick”, “123 Main St”– Number = Stores Numbers - “1, 2, 3,...”, “3.14”Number = Stores Numbers - “1, 2, 3,...”, “3.14”– Boolean = Stores True/FalseBoolean = Stores True/False– Date = Stores DateDate = Stores Date– Currency = Currency format – “Dollar, Yen”Currency = Currency format – “Dollar, Yen”– Variant = Stores AnythingVariant = Stores Anything

And there are many more!!!!And there are many more!!!!

Quick Review of Class 1Quick Review of Class 1

Naming convention for Variables:Naming convention for Variables:– Strings – Starts with “str”Strings – Starts with “str”

» strFirstNamestrFirstName

– Integers – Starts with “int”Integers – Starts with “int”» intCountintCount

– Boolean – Starts with “bln”, “bol”, “bool”Boolean – Starts with “bln”, “bol”, “bool”» boolExitboolExit

– Variant – Starts with “var”Variant – Starts with “var”» varAnyValuevarAnyValue

Quick Review of Class 1Quick Review of Class 1

A variable needs to be declaredA variable needs to be declared

Syntax: Dim Syntax: Dim variablenamevariablename [As type] [As type]

– Dim = Dimension (make space for it)Dim = Dimension (make space for it)– variablename = Ex: strFirstNamevariablename = Ex: strFirstName– [As type] = Optional, Ex: As String[As type] = Optional, Ex: As String

Dim strFirstName As StringDim strFirstName As String

ConstantsConstants

A constant is a storage for a value that does A constant is a storage for a value that does not change during code executionnot change during code execution– 3.1415, vbYes, vbRed3.1415, vbYes, vbRed– Can be changed manually Can be changed manually

» Going from 365 days to 360 days when calculating Going from 365 days to 360 days when calculating interestinterest

ConstantsConstants

Naming Conventions for ConstantsNaming Conventions for Constants– Use UPPERCASEUse UPPERCASE

» PIPI

– Start with “con” Start with “con” » conInterestconInterest

ConstantsConstants

Constants must to be declaredConstants must to be declared– Syntax: Syntax:

Const Const constnameconstname [As type] = Expression [As type] = Expression

– Const = Declares it as a ConstantConst = Declares it as a Constant

– constnameconstname = Ex: PI = Ex: PI

– [As type] = Optional, Ex: As Double[As type] = Optional, Ex: As Double

– Expression = Value assigned to it, Ex: 3.1415Expression = Value assigned to it, Ex: 3.1415

Const PI As Double = 3.1415Const PI As Double = 3.1415

Changing ConstantsChanging Constants

A Constant Value cannot ChangeA Constant Value cannot Change– You can change Constants manually by You can change Constants manually by

declaring several Constantsdeclaring several Constants» Const LONGYEAR as Integer = 365Const LONGYEAR as Integer = 365

» Const SHORTYEAR as Integer = 360Const SHORTYEAR as Integer = 360

– Let the user make the choice on a form which Let the user make the choice on a form which Constant to useConstant to use

» Example: Option buttonsExample: Option buttons

ConstantsConstants

Constant values are hard-codedConstant values are hard-coded– Need to change it directly in the codeNeed to change it directly in the code

VariantsVariants

Why not use Variants for all Variables and Why not use Variants for all Variables and Constants?Constants?– It is slowerIt is slower

» Uses up more memoryUses up more memory

» Has to be convertedHas to be converted

– Sacrifices readability of code (Programmer)Sacrifices readability of code (Programmer)» varCount – Does it count by whole numbers, or by varCount – Does it count by whole numbers, or by

fractional numbers?fractional numbers?

Option ExplicitOption Explicit

Using “Option Explicit” forces all Variables to be Using “Option Explicit” forces all Variables to be declared before the code can rundeclared before the code can run

Good for catching errorsGood for catching errors

Option ExplicitOption ExplicitDim curBonus as CurrencyDim curBonus as CurrencyDim curSalary as CurrencyDim curSalary as Currency……curBonus = curSalry * 0.1curBonus = curSalry * 0.1……

Error Message (“Variable not defined”)Error Message (“Variable not defined”)

curSalry

Option ExplicitOption Explicit

There is no set rule that says all Variables There is no set rule that says all Variables need to be declared – it is just good practiceneed to be declared – it is just good practice– With Option Explicit you are forced to declareWith Option Explicit you are forced to declare

With Option Explicit, you cannot use With Option Explicit, you cannot use “temporary” variables without declaring “temporary” variables without declaring themthem

Lifetime/Visibility of VariablesLifetime/Visibility of Variables

Public

Form

Local

Visible to the procedure where it is declared

Visible to all procedures within the form

Visible to all procedures within the project (database)

Lifetime/Visibility of VariablesLifetime/Visibility of Variables

Local LevelLocal Level– Visibility and Lifetime of variables are within Visibility and Lifetime of variables are within

the procedure that called itthe procedure that called itExample: Declaring the variable within a Example: Declaring the variable within a button’s On Click Event.button’s On Click Event.

The variable is destroyed after the code ends The variable is destroyed after the code ends (except Static variable – Next class!).(except Static variable – Next class!).No other procedure (button) can access the No other procedure (button) can access the variable.variable.

Lifetime/Visibility of VariablesLifetime/Visibility of Variables

Form1Form1

Private Sub MyButton_Click()Private Sub MyButton_Click()Dim strName As StringDim strName As StringstrName = “John”strName = “John”MsgBox strNameMsgBox strName

End SubEnd Sub

MyButton1 MyButton2

??????

Cannot see strName

Lifetime/Visibility of VariablesLifetime/Visibility of Variables

Form LevelForm Level– Visibility and Lifetime of variables are within Visibility and Lifetime of variables are within

the form for all procedures.the form for all procedures.Declaring the variable in General Declarations Declaring the variable in General Declarations section (Top) of the form.section (Top) of the form.

The variable is destroyed after the form is The variable is destroyed after the form is closed.closed.

Lifetime/Visibility of VariablesLifetime/Visibility of VariablesForm1Form1

Dim strName As StringDim strName As String

Private Sub MyButton1_Click()Private Sub MyButton1_Click()strName = “John” strName = “John” MsgBox strNameMsgBox strName

End SubEnd SubPrivate Sub MyButton2_Click()Private Sub MyButton2_Click()

MsgBox strNameMsgBox strNameEnd SubEnd Sub

MyButton1

MyButton2

Lifetime/Visibility of VariablesLifetime/Visibility of Variables

PublicPublic– Visibility and Lifetime of variables are within Visibility and Lifetime of variables are within

the project (database).the project (database).Declaring the variable as Public in General Declaring the variable as Public in General Declarations section in a standard module. Declarations section in a standard module.

The variable is destroyed after you close the The variable is destroyed after you close the project. project. All procedures (buttons, etc.) have access to the All procedures (buttons, etc.) have access to the variable as long as the project is runningvariable as long as the project is running

Lifetime/Visibility of VariablesLifetime/Visibility of Variables

Form1Form1

Private Sub MyButton1_Click()Private Sub MyButton1_Click()

strName = “John” strName = “John” MsgBox strNameMsgBox strName

End SubEnd Sub

Form2Form2

Private Sub MyButton2_Click()Private Sub MyButton2_Click()

MsgBox strNameMsgBox strName

End SubEnd Sub

MyButton1 MyButton2

Module1

Public strName as String

Review – Class 2Review – Class 2

Constants can change, but not its valueConstants can change, but not its value Avoid declaring all variables as VariantsAvoid declaring all variables as Variants Option Explicit is good for catching errorsOption Explicit is good for catching errors Lifetime and Visibility of variables are Lifetime and Visibility of variables are

(simplified):(simplified):– Local: Within the procedureLocal: Within the procedure– Form : All procedures within the formForm : All procedures within the form– Public: All procedures within the projectPublic: All procedures within the project

Next Class…Next Class…

Static VariablesStatic Variables MsgBox and InputBoxMsgBox and InputBox