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Chapter 7. Enhancing User Interaction Through Programming. 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. Tools Covered in This Chapter. - PowerPoint PPT Presentation
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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
Succeeding in Business with Microsoft Access 2010 3
Tools Covered in This Chapter (continued)
• If statement• Immediate window• Variables• Visual Basic editor• Visual Basic for Applications• Watches window
Succeeding in Business with Microsoft Access 2010 4
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
Succeeding in Business with Microsoft Access 2010 5
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
Succeeding in Business with Microsoft Access 2010 6
Understanding Visual Basic for Applications (continued)
• Coding• Statement• Event-driven language• Object-oriented language
Succeeding in Business with Microsoft Access 2010 7
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
Succeeding in Business with Microsoft Access 2010 8
Frequently Used Access Events
Succeeding in Business with Microsoft Access 2010 9
Common Events for Selected Controls
Succeeding in Business with Microsoft Access 2010 10
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
Succeeding in Business with Microsoft Access 2010 11
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
Succeeding in Business with Microsoft Access 2010 12
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
Succeeding in Business with Microsoft Access 2010 13
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
Succeeding in Business with Microsoft Access 2010 14
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
Succeeding in Business with Microsoft Access 2010 15
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
Succeeding in Business with Microsoft Access 2010 16
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
Succeeding in Business with Microsoft Access 2010 17
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
Succeeding in Business with Microsoft Access 2010 18
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
Succeeding in Business with Microsoft Access 2010 19
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
Succeeding in Business with Microsoft Access 2010 20
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
Succeeding in Business with Microsoft Access 2010 21
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
Succeeding in Business with Microsoft Access 2010 22
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
Succeeding in Business with Microsoft Access 2010 23
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
Succeeding in Business with Microsoft Access 2010 24
Testing an Event Procedure
• Switch to form view• Navigate through records – Make sure results correct in different situations
Succeeding in Business with Microsoft Access 2010 25
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
Succeeding in Business with Microsoft Access 2010 26
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
Succeeding in Business with Microsoft Access 2010 27
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
Succeeding in Business with Microsoft Access 2010 28
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
Succeeding in Business with Microsoft Access 2010 30
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
Succeeding in Business with Microsoft Access 2010 31
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
Succeeding in Business with Microsoft Access 2010 32
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
Succeeding in Business with Microsoft Access 2010 33
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
Succeeding in Business with Microsoft Access 2010 34
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
Succeeding in Business with Microsoft Access 2010 37
Using an ElseIf Statement in an If Statement (continued)
• Dim statement– Declare variables and associated data types in
procedure
Succeeding in Business with Microsoft Access 2010 38
Verifying Data with VBA
• Before Update event – Occurs before changed data in control or record
updated in database– Use to verify entered data
Succeeding in Business with Microsoft Access 2010 39
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
Succeeding in Business with Microsoft Access 2010 40
Designing the Field Validation Procedure to Verify Zip Codes (continued)
• Val function – Returns numbers contained in specified string as
numeric value
Succeeding in Business with Microsoft Access 2010 41
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
Succeeding in Business with Microsoft Access 2010 42
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
Succeeding in Business with Microsoft Access 2010 43
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
Succeeding in Business with Microsoft Access 2010 44
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
Succeeding in Business with Microsoft Access 2010 45
Level 2 Summary
• ElseIf statement • Case Select statement• Verify data using VBA
Succeeding in Business with Microsoft Access 2010 46
Level 3 Objectives: Testing and Exploring VBA
• Troubleshoot VBA procedure errors• Compile modules• Develop sources for learning VBA
Succeeding in Business with Microsoft Access 2010 47
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
Succeeding in Business with Microsoft Access 2010 48
Syntax Error Message
Succeeding in Business with Microsoft Access 2010 49
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
Succeeding in Business with Microsoft Access 2010 50
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
Succeeding in Business with Microsoft Access 2010 51
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
Succeeding in Business with Microsoft Access 2010 52
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
Succeeding in Business with Microsoft Access 2010 53
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
Succeeding in Business with Microsoft Access 2010 54
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
Succeeding in Business with Microsoft Access 2010 55
Add Watch Dialog Box
Succeeding in Business with Microsoft Access 2010 56
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
Succeeding in Business with Microsoft Access 2010 57
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
Succeeding in Business with Microsoft Access 2010 58
Visual Basic Help Table Of Contents
Succeeding in Business with Microsoft Access 2010 59
Level 3 Summary
• Errors– Syntax – Compilation– Execution or run-time
• Debugger– Use to find and correct errors
• Help– Learn more about VBA
Succeeding in Business with Microsoft Access 2010 60
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