As noted earlier, a form is the
active form in an application when the focus
in the application is within that form. This
could mean that either the form itself has the
focus or that a control on the form has focus.
The user can tell which form is active because
the title bar appears highlighted, and the form
usually appears on top of the user';s desktop.
A form receives an Activate event
when it becomes the active form and a Deactivate
event when it loses its active status to another
form in the same application. The Activate and
Deactivate event procedures are ideal places
to put code that needs to react to the user';s
navigation between forms.
Forms also support GotFocus and
LostFocus events, as do controls. You might
think that GotFocus and LostFocus event procedures
would be good places to put code that reacts
to a user entering and leaving a form in a multi-form
application.
However, a form';s GotFocus
and LostFocus events do not usually fire: A
form can only receive focus if it contains no
visible enabled controls. Because most forms
have at least one visible enabled control, GotFocus
and LostFocus don';t normally fire on forms
when the user moves between forms in an application.
NOTE 1 :
Choosing Between the Activate and Load Events.
When a form first loads into memory and immediately
displays (either because it';s the application';s
startup form or because, say, you';ve used
the Show method to load the form), the Activate
event happens after the Load event. The Activate
event procedure is a better place than the Load
event procedure to put startup code that affects
the form';s appearance (such as calls to
the graphics methods) or code that manipulates
Data-Bound controls.
This is because the Load event happens a bit
too early for some of these operations to have
their proper effect. In fact, putting some types
of code in the Load event procedure can cause
a runtime error if the code tries to manipulate
runtime properties of controls that aren';t
fully initialized.
NOTE 2 : Navigation Events Happen Only With
Respect to the Current application. Activate, DeActivate, GotFocus, and
LostFocus occur only with respect to movement between forms within the current
application. When the user changes to or returns from another application, none
of these events occur.
