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SUNY Morrisville-Norwich Campus-Week 12. CITA 130 Advanced Computer Applications II Spring 2005 Prof. Tom Smith. Objectives. Questions from Last Week Introduction to VBA Database Review. Microsoft Office Access 2003. Tutorial 11 – Using and Writing Visual Basic for Applications Code. - PowerPoint PPT Presentation
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SUNY Morrisville-Norwich Campus-Week
12
CITA 130 Advanced Computer Applications II
Spring 2005Prof. Tom Smith
Objectives Questions from Last Week Introduction to VBA Database Review
Microsoft Office Access 2003
Tutorial 11 – Using and Writing Visual Basic for Applications
Code
Learn about VBA When you work in Access, in the background,
Visual Basic for Applications (VBA) code is being created.
You can also write your own VBA code that will alter the properties of objects, perform calculations, and many other custom actions.
Recall that an event is something that happens while using the database.
You can write a statement that, when an event occurs, responds by executing a series of VBA statements.
Function procedures, Sub procedures, and modules Statements are grouped together into procedures,
which can be either a function or a Sub procedure. Common procedures are usually stored together
into a module. A module can be a standard module (stored in
memory with other database objects) or it can be a class module (stored in association with a particular form or report).
With class modules, the procedures are available by the form or report for which the class module was created.
The structure of a VBA module
Learning VBA takes time and effort Learning to write VBA code efficiently and
accurately is the hardest part of learning to use Access.
In this tutorial, you are getting just a small view of VBA code.
You should keep in mind that you will not be considered a proficient VBA programmer following this tutorial.
Rather, if you want to be a database developer, you should probably take another course geared towards VBA programming.
Review and modify an existing Sub procedure in an event procedure When a class module already exists, you
can view the code for the procedures in the VBA editor: Open the property sheets for the object and then
locate the event for which the procedure is written
Click the Build button to open the Visual Basic window, which reveals the code stored in the class module
The window in which the code appears is called the Code window.
Use assignment statements Procedures are enclosed between the Sub
statement and the End Sub statement. Within a procedure, you will see statements
that work together called control structures. Assignment statements assign a value to a
field or property. In some cases, an assignment statement
might assign a new value to an object property.
You can make changes to VBA code in the Code window.
Event properties for a form
The Visual Basic Code window
Recognize VBA statements In the Code window (shown in the previous slide) you would
view, edit, and test your VBA statements. You will probably not understand the statements that
appear in this window. However, there are a couple of statements that you will
recognize: The first statement is the Private Sub statement The last statement is the End Sub statement
In this sample code, the ForeColor is changed under certain circumstances. The code used the RGB function, which will return a specified
colored by using combinations of Red, Green, and Blue
A function that modifies an object’s color
RGB values for some colors
Create Function proceduresin a standard module To create new procedures click Modules on the
objects bar and then click New. This will open the Code window in the Visual
Basic window. To write a Sub procedure,begin with the Sub
statement. To write a Function procedure, begin with the
Function statement. The Function will end with the End Function
statement.
Assign a name to a function The Function statement is then followed
with the name of the function. If you will be passing values to the
Function, the Function name is followed by a Parameter list (which could be just one item).
When you pass a value to a Function, it is called an argument.
When naming a Sub procedure or a function, you must follow the rules for naming objects.
Define a function in the Code window
Name and save your module Once you have written your Function, you will
need to save the module that holds the function. When you click the Save button, you will be
prompted to supply a name for the module. This is not the same as naming the Function and
you do not have to follow the name rules mentioned previously.
Recall that a module will hold a collection of procedures so you will want to name the module something that will indicate what is inside the module.
Use comments in your functions
Create event procedures VBA is an event-driven language, meaning
that when events takes place, procedures are triggered.
All event procedures are Sub procedures. Access will automatically name the event
in a standard way, which includes: The name of the control An underscore The event name
Add an event procedure To add an event procedure to a class module:
Open the object to which it will be attached Open its property sheet On the Event tab, select the event that will trigger the
function This will open the code window for the object you
have selected. Before you run your procedure, it must first be
compiled. The process of compilation is the process of
converting the code to a format the computer can understand.
Use the If statement A commonly used control structure is the If
statement The If statement provides a condition and then if
the condition is true, a set of statements is executed; if it is false, a different set of statements is executed.
The If statement created in your tutorial incorporates the IsNull function into it.
The IsNull function returns a True value if the argument is empty (no text) and it returns a False value if the argument is not empty.
An example of an If statement
The function execution process
An example of an event procedure
Declare variables in functions and procedures
Primary VBA Data Types
Compile and test Function procedures, Sub procedures and event procedures When you compile a module, Access will look for
errors in syntax. If any errors are found, an error message will display.
You will need to fix all syntax errors before the modules can complete compilation.
When no errors exist, Access will translate the procedure.
You should compile a module any time you make changes to make sure there are no syntax errors in its procedures.
You should also test each procedure to make sure it performs as you expect.
Database Review Questions? Databases/Tables Queries Reports Forms VBA