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Enhancing User Interaction Through Programming
Chapter 7 Enhancing User Interaction Through Programming Use the quote as a jumping off point for discussion, if desired.
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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
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Tools Covered in This Chapter
Assignment statement Breakpoints Code window DateDiff function DateSerial function Debug DoCmd statement Succeeding in Business with Microsoft Access 2010
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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
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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
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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
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Understanding Visual Basic for Applications (continued)
Coding Statement Event-driven language Object-oriented language Succeeding in Business with Microsoft Access 2010
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Event-Driven Programming
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
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Frequently Used Access Events
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Common Events for Selected Controls
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Coding VBA Types of procedures Function procedures Sub 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Using the If Statement in Decision Making (Cont.)
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 Succeeding in Business with Microsoft Access 2010
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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
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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
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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
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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
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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
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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 type Succeeding in Business with Microsoft Access 2010
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Common VBA Data Types Succeeding in Business with Microsoft Access 2010
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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
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Testing a Function in the Immediate Window (continued)
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
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Level 1 Summary VBA Create procedures in module
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
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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
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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 toolbar Succeeding in Business with Microsoft Access 2010
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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 inclusive Succeeding in Business with Microsoft Access 2010
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Comparing an ElseIf Clause to an Else…if Clause
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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
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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
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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
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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
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Using the Case 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
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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
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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
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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
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Level 2 Summary ElseIf statement Case Select statement
Verify data using VBA Succeeding in Business with Microsoft Access 2010
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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
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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
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Syntax Error Message Succeeding in Business with Microsoft Access 2010
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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
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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
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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
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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
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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
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Identifying Errors Using the 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
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Add Watch Dialog Box Succeeding in Business with Microsoft Access 2010
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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
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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
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Visual Basic Help Table Of Contents
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Level 3 Summary Errors Debugger Help 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
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Chapter Summary VBA Decision structures Develop subroutines
Programming language for Microsoft Office applications Decision structures If ElseIf Case Develop subroutines Use debugger to find errors Succeeding in Business with Microsoft Access 2010
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