1 chapter 9 writing, testing, and debugging access applications

1Chapter 9Chapter 9

Writing, Testing, and Debugging

Access Applications

Writing, Testing, and Debugging

Access Applications

9Chapter ObjectivesChapter Objectives

• Write VBA procedures that use a variety of assignment statements

• Choose and write appropriate conditional execution statements

• Create program loops

• Write disk- and file-related statements

9Chapter ObjectivesChapter Objectives

• Invoke error handlers and write error-handling routines

• Test Access applications

• Debug Access applications using message boxes and the debugging facilities

9OperatorsOperators

• Many VBA statements support mathematical, string, and comparison operations

• Integer division Indicated by \

• Exponentiation Indicated by the ^ operator

9OperatorsOperators

• Comparison operators <, <=,>, >=, =, and <>

• And and Or Logical operators

• Not Negative operator

• And, Or, and Not have traditional precedence relationships Parentheses can be used to control the precedence

9OperatorsOperators

• String concatenation Uniting of two or more string values Can be performed using either the + or &

operator+ operator produces a null result when either

operand is null& operator treats a null operand as a zero-length

string

9OperatorsOperators

Figure 9-1 Constructing an SQL command by using strings in VBA

9CommentsComments

• Comments Indicate the purpose of each section of code

• Rem statements Used to include explanatory comments in a

program Can be represented in code with a single quote

(‘)

9Built-in FunctionsBuilt-in Functions

• Built-in functions Perform trigonometric calculations, financial

calculations, and common mathematical calculations

Handle the conversion of data from one data type to another

InputBoxUsed to prompt a user for information

9 Assignment and With Statements

Assignment and With Statements

• Assignment statements Change the value of an object’s properties Use them to update fields in recordsets and to

place values in VBA variables

• With statements Allow you to abbreviate assignment statements

that reference object properties, because the object does not need to be specified



Table 9-1 Summary of assignment statements



Table 9-1 Summary of assignment statements (continued)

9 Conditional Execution Statements (If Statement)

Conditional Execution Statements (If Statement)

• If statement Can evaluate multiple conditions and thus

selectively execute multiple sections of code Can also contain multiple ElseIf parts

When it does include such parts, conditions occur for the initial If part and for each ElseIf part

9 Iterative (Looping) Statements

Iterative (Looping) Statements

• Iterative (or looping) statements Cause blocks of statements to repeat

• VBA supports multiple looping statement forms The Do statement is a commonly used

“looping” statement

9 Iterative (Looping) Statements

Iterative (Looping) Statements

Table 9-2 Looping statements

9 Unconditional Branching Statements

Unconditional Branching Statements

• Unconditional branching statements Cause the program to skip execution of code

that would have otherwise been executed Created using line labels and numbers

• Exit Function Exits a function

9 VBA Statements and Related Functions that Perform Access Actions

VBA Statements and Related Functions that Perform Access Actions

• VBA provides many statements that may not appear elsewhere which include statements that: Manipulate the Access environment Manipulate files Reference the Windows environment Manipulate other Windows applications

9 Statements Related to the Access Environment

Statements Related to the Access Environment

• SendKeys statements are useful when you want to trigger a series of events

Table 9-3 Statements that perform actions within the Access environment

9 Statements Related to the Access Environment

Statements Related to the Access Environment

Table 9-3 Statements that perform actions within the Access environment (continued)

9 Windows Disk- and File-Related Statements

Windows Disk- and File-Related Statements

• ChDrive Changes the current drive

• ChDir Changes the current directory

• CurDir[] function Returns the current directory



Table 9-4 Disk- and file-related statements



Table 9-5 File I/O statements

9 Determining and Setting the Applications Operating Environment

Determining and Setting the Applications Operating Environment

• An application can: Determine the path to an application by reading

the Windows Registry Access information about the registry through

the GetSetting and GetAllSettings functions

9 Determining and Setting the Applications Operating Environment

Determining and Setting the Applications Operating Environment

Table 9-6 Commonly used SysCmd specifications

9 Using SysCmd to Implement a Progress Meter

Using SysCmd to Implement a Progress Meter

• A Progress meter should be used whenever an operation is expected to take a long time acSysCmdInitMeter constant

Used to start the progress meter and length of argument indicates the total time of the operation

acSysCmdRemoveMeter constantUsed when the operation is complete

acSysCmdUpdateMeter constantUsed to show progress at a given point in time

9Compilation ErrorsCompilation Errors

• Compilation errors Due to syntax mistakes

• Compiling a procedure tells Access to translate VBA code into a format that is efficiently executed by the computer

• A procedure will not compile when one or more lines of code violate the syntax rules of VBA

9Runtime ErrorsRuntime Errors

• When a statement combination is invalid, errors may occur when the procedure executes

Figure 9-2 Runtime error example

9Logic ErrorsLogic Errors

• A logic error occurs when a procedure executes successfully but produces an incorrect result

• Common logic errors include: Procedures associated with events that do not

execute Procedures associated with events that execute

at an unplanned time

9Logic ErrorsLogic Errors

• Common logic errors (continued): Events execute in an unplanned sequence Focus of a control, form, or report changes

earlier or later than a procedure expects Value of a control changes earlier or later than

an executed procedure expects Criteria string used by a method is incorrect An expression that does not accommodate null

values o empty strings receives one

9The On Error StatementThe On Error Statement

• On Error statement Principal means for controlling error processing

in VBA

• When VBA encounters an On Error statement, it enables an error handler Error handler

A mechanism for transferring process control to specific VBA statements when an error occurs

9 The Resume, Exit, and End Statements

The Resume, Exit, and End Statements

• An error-handling routine runs until it encounters a Resume, Exit, or End statement Resume statement

Causes the system to continue processing Exit statement

Causes the system to end the error-handling routine End statement

The last statement in a procedure

9Advanced Error HandlingAdvanced Error Handling

• Err Commonly used error-handling object Belongs to VBA object library Specializes in handling VBA runtime errors

• Err object properties and methods including: Description property

Contains the Access default description of the error that just occurred

9Advanced Error HandlingAdvanced Error Handling

• Err object properties and methods including (continued): Number property

Contains the Access internal error number for the most recent error

Clear methodAutomatically sets the Number property to zero

9 Handling Logic Errors by Using MsgBox

Handling Logic Errors by Using MsgBox

• One technique for understanding the underlying logic of your code is to include MsgBox statements in the code Display the value of variables as the code

executes When values are displayed, you can see what is

actually happening in the procedure and compare that to what you think should be happening

9 Using VBA’s Debug Facility to Find and Solve Complex Logic Errors

Using VBA’s Debug Facility to Find and Solve Complex Logic Errors

• Simplest way to interact with the Debug facility is to use the Print method in conjunction with the Debug object

• Debug object Allows a program to communicate with the

Debug facility Supports Assert and Print methods

9 Using VBA’s Debug Facility to Find and Solve Complex Logic Errors

Using VBA’s Debug Facility to Find and Solve Complex Logic Errors

Figure 9-3 The Immediate window of the Debug facility

9 Breakpoints, Step into, and Step Over

Breakpoints, Step into, and Step Over

• Breakpoint Suspends the execution of a procedure

• Step Into and Step Over menu items Used to execute one statement in a procedure at a time

• VBA Toggle Breakpoint Allows programmer to examine state of the processing

at the time when the statement executed

• Clear All Breakpoints option Clears all breakpoints set previously



• Step Into menu item Causes execution to continue to progress one

statement at a time inside the invoked procedure

If the statement being executed invokes a procedure or a function, then Step Into will enter that procedure or function, allowing you to debug it as well



• Step Over menu item If the statement being executed invokes a

procedure or a function, Step Over does not go into the procedure or function

• Run to Cursor item in the Debug menu Causes Access to continue processing until it

reaches the point where you have placed your cursor and then procedure will then suspend processing



• When you select the Continue item on the Run menu, Access will continue processing the procedure until it reaches another breakpoint

• Reset menu item Resets the internal representation of the code so

that the execution environment returns to what it would be before the procedure is executed



• Set Next Statement option Causes the system to move to the statement that

currently contains the cursor and makes it the next executable statement

• Show Next Statement option Displays the next executable statement in the

procedure

9 Using Watch Expressions to Find Logic Errors

Using Watch Expressions to Find Logic Errors

• Watch window allows your code to break on changes in the variable that you want to analyze

Figure 9-4 The Add Watch window



• You can change or delete watch expressions by using the Edit Watch menu item

Figure 9-5 The Edit Watch window



• Locals window Displays the current values of all expressions

encountered in the procedure currently being executed

Figure 9-6 The Locals window

9Call Stack WindowCall Stack Window

• Call Stack window Shows the sequence of procedures that were

invoked, leading to the suspended procedure

Figure 9-7 The Call Stack window

9 Repairing and Compacting a Database

Repairing and Compacting a Database

• Corrupt application Occurs when an error affects the Access internal

representation of an application’s tabled, forms, reports, procedures, and macros

• Symptoms of a corrupt application Access may recognize when the application is corrupt

and notify the user when the application is opened Application may run in a strange and unpredictable

fashion

9Chapter SummaryChapter Summary

• Statements Accomplish an objective by organizing the objects,

variables, and expressions used in a procedure Assign values to properties, influence the execution of

a procedure, and change aspects of Access environment

• To build an Access application, a developer must construct statements, order them inside a procedure, and determine when the procedure should execute


• VBA supports several types of statements Assignment statement Object variables require the Set statement With statement Conditional Execution statements

Provided in the form If…Then…Else and If…Else statements

Select Case statement


• VBA supports several looping statements For Next Loop, the Do While loop, and the Do

Until loopProvide different ways to control the number of loop

executions

Do statementsAllow the condition controlling the execution of a

loop to be placed either at the beginning or the end of the loop


• On Error statement Establishes error-handling capabilities within a

procedure

• Compilation errors Often identified as soon as statements are entered

• Runtime errors Cause Access to display an error message and highlight

the line where processing stopped


• Logic errors Can be debugged as an application is executing

• Breakpoints Suspend execution of an application

• Repair database menu item Used to repair a corrupt database

• Compacting a database Can significantly reduce the amount of storage space

required by an Access application

1 chapter 9 writing, testing, and debugging access applications

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