Working with controls. Using
Properties, Methods and Events
You use controls to
get user input and to display output. Some of the controls you can use
in your applications include text boxes, command buttons, and list
boxes. Other controls let you access other applications and process
data as if the remote application was part of your code. Each control
has its own set of properties, methods, and events that can be
modified from the properties window or from the code
Properties are simple to understand. Here's an example. A human
being, he/she has eyes, legs, arms, etc. They are all properties of
the human being.
A property describes an object, its behavior and its look. If you
wanted to change the color of the eyes you would just do this:
Human.Eyes = Brown
Human.Weight = 156
If you wanted to change any other properties, you could do that too.
As long as the property is available. For example, you cannot
do this: Human.Beak = True. The nice thing about properties is that
you do not have to know what it takes to actually change the human's
eyes or weight. You just indicate that you want it to change.
An example of this is the Label
The label control has an important property, Caption. Without it, it
would be almost useless. The Caption property sets or returns the text
presently contained in the Label control. The only drawback is that
you cannot directly enter text into the label. The text
control is virtually identical except that you can type in text.
Label.Caption = "This is really easy"
In some cases, properties aren't enough to tell an object what it
should do. It would be nice to give the object direct commands as
well. Visual Basic lets you do this. Let's go back to the Human
example. If you wanted the human to move its arm a method is a nice
and easy way of doing that. The human could have a method called
MoveArm, which we could use like an ordinary command:
As you can see, you don't give a method a value, it will execute like
any other Visual Basic command. As far as this is concerned, you
really don't care what the human has to do to move its arm. All you
want it to do is move its arm.
Q:Ok we used the
properties and the methods of an ďhumanĒ object. In the previous
example we have used the MoveArm method now how will we know when the
human has ended the MoveArm method?
A:By using an event
An event procedure is
simple to understand. These procedures are automatically declared by
Visual Basic for each object that we use and are fired when that event
Draw a button on your
form and then double click it, you will now see a procedure that looks
something like this:
This is an event
procedure and itís fired when Command1 is clicked. You can observe
the parts in the subís name: