Learn Access 2003 VBA with The Smart Method

60

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Lesson 3-2: Understand

methods

What are methods.

As well as having properties to describe an object some objects have

certain functionality too. Let’s consider a Car object. We may have

precisely described it by setting properties such as Color, NumberOfSeats

and FuelType but what is the car for. Is it a film prop, a paperweight, or

does it actually do something.

The things objects can do are called methods.

All cars have several methods such as StartEngine, MoveForward, Stop,

SteerLeft and SteerRight. Some cars have methods that are not common

to all cars such as StartAirConditioner or EnableCruiseControl.

Methods may be modified by arguments

Access objects have methods too. For example a Combo Box object has an

AddItem method.

Simply invoking the MoveForward method of the Car object wouldn’t

really be enough. To more precisely tell the car what to do we might

want to say:

Move forward three metres.

In order to do this we’d need to invoke the MoveForward method along

with some instructions telling the car how to move forwards. These

instructions are called parameters or arguments. The actual

MoveForward() method call would more likely be something like this:

MoveForward( 3 )

note

Some programmers prefer the

term Parameter instead of

Argument. Both are correct.

Session3

Session Three: The Object-Orientated Paradigm

© 2007 The Smart Method Ltd

61

Where the argument 3 represents the distance to move forwards in

metres.

Examples of methods available in Access

objects

A method with no parameters

Methods do not have to have parameters. A good example of a very

useful method is the Form object’s Requery method. Invoking the

Requery method will execute the SQL query that underpins the form and

will then update all of the controls on the form to reflect the current state

of the data.

This could be very useful in a multi-user environment when the user

wanted to be sure that the data displayed on the screen was completely

up to date.

A method with parameters

The Combo Box object has a method that allows items to be added to it.

This is intuitively named the AddItem method.

Clearly the AddItem method must have some parameters in order to tell

the Combo Box object something about the item to be added.

The method actually has two parameters. The first is the text that will be

displayed in the combo box and the second is an optional parameter to

indicate the position in the list.

For Example:

AddItem( “London")

AddItem( “Glasgow")

Would result in a combo box with two entries, the first would be London

and the second Glasgow.

AddItem( “London", 1 )

AddItem( “Glasgow", 0)

Would result in a combo box with two entries, the first would be

Glasgow and the second London.