Enhancing User Interaction Through Programming Chapter 7.

Enhancing User Interaction Through Programming

Chapter 7

Chapter Introduction

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

macros

Succeeding in Business with Microsoft Access 2010 2

Tools Covered in This Chapter

• Assignment statement • Breakpoints• Code window • DateDiff function • DateSerial function• Debug• DoCmd statement


Tools Covered in This Chapter (continued)

• If statement• Immediate window• Variables• Visual Basic editor• Visual Basic for Applications• Watches window


Level 1 Objectives:Writing Visual Basic for Applications Code

• Understand Visual Basic for Applications programming

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

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

standard module


Understanding 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


Understanding Visual Basic for Applications (continued)

• Coding• Statement• Event-driven language• Object-oriented language


Event-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


Frequently Used Access Events


Common Events for Selected Controls


Coding 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


Coding 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


Coding 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


Creating a Subroutine in a Standard Module

• Replace macros with VBA procedures– Better error handling and greater capabilities– Some tasks cannot be performed with VBA• AutoKeys• AutoExec


Creating a New Standard Module

• Click Create tab– Click Module button in the Macros & Code group

• Begin new procedure in module– Click Insert menu– Click procedure– Type name– Select options


Creating 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


Creating 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


Creating a Subroutine

• Type statements in procedure between Sub and End Sub statements

• DoCmd statement– Executes action in procedure– Access object

• Method – Function that operates on specific objects or

controls


Creating 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


Creating 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


Designing 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 list arrow– Click [event procedure]– Click Build button to right of On Current text box


Using the If Statement in Decision Making

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

of condition– In simplest statement, Access executes a group of

statements if the condition is true• Executes nothing if False


Using the If Statement in Decision Making (Cont.)

• If statement– Tests condition follows one of two paths

depending on outcome of condition– General form

If condition ThenTrue-statement group

[ElseFalse-statement group]

End If


Using the If Statement in Decision Making (Cont.)

• 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

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


Testing an Event Procedure

• Switch to form view• Navigate through records – Make sure results correct in different situations


Using a Function in a Standard Module

• Similar calculation requests– Create function to perform calculation – Eliminates possibility of error when entering code

in more than one place• Function – Begins with Function statement – Ends with End Function statement


Using Functions

• Similar to way built-in functions used• Call a function– Function name followed by argument(s)– Commas separate multiple arguments

• DateDiff function– Calculates number of time intervals between two

dates


Using Variables

• 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


Using Variables (continued)

• Naming rules (applies to subroutine and function names also)– 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 typeSucceeding in Business with Microsoft Access 2010 29

Common VBA Data Types


Testing 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


Testing 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– Access executes the function and prints the value

returned by the function


Level 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


Level 2 Objectives:Using Custom Functions and Verifying Data

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

• Verify data using event procedures• Use the Case control structure


Enhancing an Event Procedure to Use a Custom Function

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

Design view– 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 Visual Basic toolbarSucceeding in Business with Microsoft Access 2010 35

Using 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

inclusiveSucceeding in Business with Microsoft Access 2010 36

Comparing an ElseIf Clause to an Else…if Clause


Using an ElseIf Statement in an If Statement (continued)

• Dim statement– Declare variables and associated data types in

procedure


Verifying Data with VBA

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

updated in database– Use to verify entered data


Designing 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


Designing the Field Validation Procedure to Verify Zip Codes (continued)

• Val function – Returns numbers contained in specified string as

numeric value


Using 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


Using the Case Control Structure (continued)

• CancelEvent action – Cancels event that caused procedure or macro

containing action to execute• SetFocus – Moves focus to specified object or control


Testing the Field Validation Procedure

• Switch to form view to test validation procedure

• Using event procedure for control or form– Before Update event for each control on form– Disadvantage• All changes made to record canceled


Designing the Field Validation Procedure to Verify Phone Area Codes

• Must test first three digits of phone number• Message can suggest potential error– Must accept any phone area code entry


Level 2 Summary

• ElseIf statement • Case Select statement• Verify data using VBA


Level 3 Objectives: Testing and Exploring VBA

• Troubleshoot VBA procedure errors• Compile modules• Develop sources for learning VBA


Troubleshooting 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


Syntax Error Message


Troubleshooting 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


Troubleshooting 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


Using 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


Using 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


Using 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

• Recompile and save

• When done, click Debug and Clear all Breakpoints


Identifying 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


Add Watch Dialog Box


Building 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• Easier to correct small groups than long procedure


Using Help to Learn More About Programming and VBA

• Access Help contains valuable information about VBA

• Can access Office.com for help if online• If not online, uses Help downloaded at

installation• Search for a topic– Returns results list– Can view sample code for situations


Visual Basic Help Table Of Contents


Level 3 Summary

• Errors– Syntax – Compilation– Execution or run-time

• Debugger– Use to find and correct errors

• Help– Learn more about VBA


Chapter Summary

• VBA– Programming language for Microsoft Office

applications• Decision structures– If– ElseIf– Case

• Develop subroutines• Use debugger to find errorsSucceeding in Business with Microsoft Access 2010 61

Enhancing User Interaction Through Programming Chapter 7.

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