xp chapter 7 succeeding in business with microsoft office access 2003: a problem-solving approach 1...

Chapter 7 Succeeding in Business with Microsoft Office Access 2003: A Problem-Solving Approach

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XP

Enhancing User Interaction Through Programming

Chapter 7

“I like thinking big. If you’re going to be thinking anything, youmight as well think big.”

—Donald Trump


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XPChapter Introduction

• Visual basic for applications (VBA) Fully customize and automate a database Perform more complex validity Use functions and actions not available with macros


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XPTools Covered in This Chapter

• Assignment statement

• Breakpoints

• Code window

• DateDiff function

• DateSerial function

• Debug

• DoCmd statement


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XPTools Covered in This Chapter (continued)

• If statement

• Immediate window

• Northwind sample database

• Variables

• Visual basic editor

• Watches window


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XPLevel 1 Objectives:Writing Visual Basic for

Applications Code

• Design create and test a subroutine in a standard module

• Design create, and test an event procedure

• Analyze decisions using procedures

• Design create, and test a function in a standard module


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XPUnderstanding Visual Basic for Applications

• Programming language for Microsoft Office programs Including Access

• Common syntax and set of common features for all Microsoft Office programs

• Features unique for each Microsoft Office program

• Use programming language Write set of instructions to direct computer to perform

specific operations in specific order


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XPUnderstanding Visual Basic for Applications (continued)

• Coding

• Statement

• Event-driven language

• Object-oriented language


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XPEvent-Driven Programming

• Event State condition or occurrence that Access recognizes Has associated event property Appear in property sheet for forms reports, and

controls

• Create group of statements using VBA code Set event property value to name of that group of

statements Event procedure


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XPFrequently Used Access Events


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XPFrequently Used Access Events (continued)


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XPCommon Events for Selected Controls


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XPCoding VBA

• Types of procedures Function procedures

• Performs operations • Returns value • Accepts input values • Can be used in expressions

Sub procedures• Performs operations and accepts input values • Does not return value • Cannot be used in expressions


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XPCoding VBA (continued)

• Module Group of related procedures Starts with declarations section One or more procedures

• Basic types of modules Standard modules

• Database object stored in memory• Use from anywhere in database

Class modules• Usually associated with particular form or report


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XPCoding VBA (continued)

• Public procedure More than one object can use

• Local procedure or a private procedure Only the form or report for which class module created

can use event procedure


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XPCreating a Subroutine in a Standard Module

• Replace macros with VBA procedures Some tasks cannot be performed with VBA

• AutoKeys• AutoExec


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XPCreating a New Standard Module

• Click modules tab Click new button

• Begin new procedure in module Click list arrow on insert module button Click procedure Type name Select options


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XPCreating a New Standard Module (continued)

• Visual Basic Editor Create and modify VBA code

• Visual Basic window Program window that opens within VBE

• Code window Window to create modify and display specific VBA

procedures Can have as many code windows open as modules in

database


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XPCreating a New Standard Module (continued)

• Sub statement Ends with end sub statement Includes

• Scope of procedure• Name of procedure • Opening and closing parenthesis

• Option compare statement Designates technique access uses to compare and

sort text data


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XPCreating a Subroutine

• Type statements in procedure between Sub and End Sub statements

• DoCmd statement Executes action in procedure Access object

• Method Action that operates on specific objects or controls


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XPCreating a Subroutine (continued)

• Comment Include anywhere in VBA procedure Describe what procedure or statement does

• Make it easier for programmers to identify purpose of statements

Begin comment with • Word Rem (for “remark”) • Or single quotation mark (')

Appear green in code window


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XPCreating a Subroutine (continued)

• Line label Statement that serves as starting point for block of

statements in procedure Begins at start of line and ends with colon

• Underscore character at end of line Statement continues to next line

• Run procedure Click Run Sub/Userform button

• Saves module Click Save button


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XPCreating an Event Procedure


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XPDesigning an Event Procedure

• Associate procedure with form’s On Current event property Triggered when form’s Current event occurs Occurs when focus moves to record

• Add event procedure Open property sheet for form Click On Current text box Click list arrow Click [event procedure] Click Build button to right of On Current text box


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XPMaking Decisions Using the If Statement

• Decision-making statement Executes group of statements based on outcome of

condition


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XPMaking Decisions Using the If Statement (continued)

• If statement Tests condition follows one of two paths depending on

outcome of condition General form

If condition Then

True-statement group

[Else

False-statement group]

End If


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• Assignment statement Assigns value of expression to control or property Example

• EstSalary.ForeColor = vbGreen

• ForeColor property

• Color constants Predefined VBA names Have values that represent system color value


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XPComparison Operators and How to Use Them in Conditions


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• IsNull function returns True value when field or control null False when not


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XPTesting an Event Procedure

• Switch to form view

• Navigate through records Make sure results correct in different situations


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XPCreating a Function

• Similar calculation requests Create function to perform calculation

• Function Begins with Function statement Ends with End Function statement


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XPVariables

• Named location in computer memory

• Can contain value

• Use to store and retrieve data

• Reference using variable name assigned to location

• Holds only one value at a time


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XPVariables (continued)

• Naming rules Must begin with letter Cannot exceed 255 characters Include letters numbers and underscore character Cannot use space, punctuation, or special characters Cannot be same as keywords or reserved words

• Each variable has data type


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XPCommon VBA Data Types


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XPUsing Functions

• Similar to way built-in functions used

• Call function Function name followed by argument(s) Commas separate multiple arguments

• DateDiff function Calculates number of time intervals between two dates


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XPTesting a Function in the Immediate Window

• When statement entered Editor checks statement to make sure syntax correct

• Logic error Occurs when procedure produces incorrect results

• Immediate window Test VBA procedures without changing data in

database Enter different values to test procedure


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XPTesting a Function in the Immediate Window (continued)

• Immediate window Type keyword “print” or question mark (?) Followed by procedure name and argument values to

test in parentheses and separated by commas

• DateSerial function Returns date value for specified year, month, and day


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XPLevel 1 Summary

• VBA Programming language for Microsoft Office programs

• Create procedures in module

• Event-driven programming Program statement execution triggered by events

• If statement Used to make decisions

• Function Returns a value


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XPLevel 2 Objectives:Using Custom Functions and

Verifying Data

• Design create and test a custom function in an event procedure

• Use ElseIf and If statements

• Verify data using event procedures

• Use the Case control structure


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XPEnhancing an Event Procedure to Use a Custom Function

• Add and change statements in a procedure Open object that contains event procedure in Design

view Click Code button on toolbar Add new procedure module or class module

• Click Insert on menu bar • Click Procedure, Module, or Class Module

Edit existing statements• Scroll code window to desired statement • Make necessary changes

Press Save button on Standard toolbar


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XPUsing an ElseIf Statement in an If Statement

• Date function Returns current computer system date

• ElseIf statement Equivalent to Else clause followed by If statement

• Choice of which If statement version used Matter of personal preference

• Arranging order of condition testing Order of condition testing critical Place conditions in order from least inclusive to most

inclusive


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XPComparing an ElseIf Clause to an Else…if Clause


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XPUsing an ElseIf Statement in an if Statement (continued)

• Dim statement Declare variables and associated data types in

procedure


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XPVerifying Data with VBA

• Before Update event Occurs before changed data in control or record

updated in database Use to verify entered data


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XPDesigning the Field Validation Procedure to Verify Zip Codes

• Cancel As Integer Defines Cancel as parameter with Integer data type For some events access executes attached event

procedure before performing default behavior Can cancel default behavior in event procedure or

macro Using Cancel parameter

• Left function Returns string containing specified number of

characters from left side of specified string


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XPDesigning the Field Validation Procedure to Verify Zip Codes

(continued)

• Val function Returns numbers contained in specified string as

numeric value


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XPUsing the Case Control Structure

• Control structure Set of VBA statements work together as a unit

• Case control structure Evaluates expression Performs one of several alternative sets of statements Based on resulting value (or condition) of evaluated

expression Use Case Else statement as last Case statement

• Include false-statement group


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XPUsing the Case Control Structure (continued)

• CancelEvent action Cancels event that caused procedure or macro

containing action to execute

• Me keyword Refers to current object

• Undo Method that clears all changes made to current record

• SetFocus Moves focus to specified object or control


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XPTesting the Field Validation Procedure to Verify Zip Codes

• Switch to form view to test validation procedure

• Using event procedure for control or form Before Update event for each control on form Need two or more fields as part of validation process

• Use form’s Before Update event Disadvantage

• All changes made to record undone


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XPDesigning the Field Validation Procedure to Verify Phone Area

Codes

• Message can suggest potential error Must accept any phone area code entry


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XPLevel 2 Summary

• ElseIf statement

• Verify data using VBA


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XPLevel 3 Objectives: Testing and Exploring VBA

• Troubleshoot problems in VBA procedures

• Compile modules

• Develop sources for learning VBA

• Explore completed modules in the Northwind sample database


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XPTroubleshooting VBA Procedures

• Syntax error Occurs when VBA statement violates language rules

for statement such as • Misspelling • Incorrect sequence of keywords• Missing parenthesis

Detected immediately when statement completed• Error message opens and explains error


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XPSyntax Error Message


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XPTroubleshooting VBA Procedures (continued)

• Compilation error Occurs when procedures translated into form computer

can understand

• Compilation Process of translating modules from VBA to form

computer understands


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XPTroubleshooting VBA Procedures (continued)

• Prevent compilation errors at run time Use Compile command on Debug menu Compile as last step before saving module

• Execution error or run-time error Occurs when procedure executes and stops because it

tries to perform operation that is impossible to perform


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XPUsing the Debugger to Correct Errors

• Breakpoint Run subroutine or function up until line on which

breakpoint set Procedure halts execution at point and displays

module screen Good way to isolate place at which procedure stops

producing anticipated result


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XPUsing the Debugger to Correct Errors (continued)

• Use mouse pointer to get more information about procedure Pointing to variable name displays ScreenTip with

value contained in variable at point that procedure halted

• Execute procedure one statement at a time Try and identify cause of error Click Debug on menu bar

• Click Step Into


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XPUsing the Debugger to Correct Errors (continued)

• Step Into Procedure executes next statement and stops

• Step Out Executes current subroutine or function and then halts

• Reset button Stops debugger so you can fix problem


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XPIdentifying Errors Using the Watches Window

• Watches window Shows current value of specified variable

• Add Watch dialog box Enter variable name to watch

• “<Out of context>” in value column Appears for watch expression When access not executing procedure that contains

watch expression


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XPAdd Watch Dialog Box


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XPBuilding Procedures Slowly to Isolate Problems

• Prevent problems in procedures Build them slowly using small groups of statements Prove them to be correct as you go


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XPExploring VBA

• Powerful but complicated language

• Takes time to learn

• Know what resources available


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XPUsing the Northwind Sample Database

• Very efficient to reuse code included in different modules

• Sample Northwind database Installed with access Study existing procedures Load by clicking help on menu bar in access

• Point to sample databases• Click Northwind sample database

Contains variety of simple and complex VBA procedures


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XPUsing Help to Learn More About Programming and VBA

• Access Help contains valuable information about VBA

• Reading individual topics gives excellent background

• Search results list Sample code for situations


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XPVisual Basic Help Table Of Contents


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XPLevel 3 Summary

• Errors Syntax Compilation Execution or run-time

• Debugger Use to find and correct errors

• Help Learn more about VBA


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XPChapter Summary

• VBA Programming language for Microsoft Office

applications

• Decision structures If ElseIf Case

• Develop subroutines

• Use debugger to find errors

xp chapter 7 succeeding in business with microsoft office access 2003: a problem-solving approach 1...

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