Teach Yourself Borland C++ in 14 Days - portal

152 Day 5
Figure 5.4.
The form with all
components added.
What we have done here is create a single event-handling function that handles the OnClick
event of both buttons. We use the Sender parameter to determine which of the two buttons
sent the OnClick event and then either hide or show the memo component as needed. We
could have created a separate OnClick handler for each button, but with this method the code
is a little more compact. Besides, it’s a good illustration of how Sender can be used.
You can see from this exercise that once you have created an OnClick event handler for a
particular component, you can attach that same handler to the OnClick event of any
component on the form. I’ll discuss more of the details of events as we move through the
book.
HOUSE RULES: EVENTS
■ You may respond to any of a component’s events as needed.
■ You are not required to respond to all events a component defines.
■ Events are handled by event-handling functions called event handlers.
■ Several components may share a common event handler.
■ Event handler names produced by C++Builder are default names and may be
changed by the programmer.
■ Be sure to change an event handler’s name only in the Object Inspector.
■ The Sender parameter of an event handler can be used to determine which
component fired the event.