Teach Yourself Borland C++ in 14 Days - portal

C++ Class Frameworks and the Visual Component Model
In this case, you are getting information on the button that was pressed, which keyboard keys
were pressed at the time the mouse was clicked, and the x,y coordinate of the cursor when
the mouse button was clicked. The event-handling function contains all the information you
need to deal with the particular event that the event handler is designed to handle.
So what exactly is Sender? Sender is a pointer to the component that is sending the message
to the message handler. In this example, the Sender parameter is extra baggage because we
know that the Show/Hide button is the sender. Sender exists to allow you to have more than
one component use the same event handler. To illustrate, let’s create a new button and have
one of our buttons be the Show button and the other be the Hide button:
1. If the Code Editor is on top, press F12 to switch back to the Form Editor.
2. Click on the Show/Hide button to select it. Change both the Name and Caption
properties to Show.
3. Add a new button to the form to the right of the Show button. Arrange the
buttons, if desired, to give an even look to the form.
4. Change the Name property for the new button to Hide. The Caption property will
also change to Hide (you’ll have to press Enter before the Caption property will
change).
5. Click the Show button and then click on the Events tab in the Object Inspector.
Notice that the OnClick event now says ShowClick. Edit it to say ButtonClick again.
(The initial event handler name is a default name. You can change it to any name
you like.)
6. Click the Hide button and find the OnClick event in the Object Inspector (it
should be selected already). Next to the value is a drop-down arrow button. Click
the arrow button and then choose ButtonClick from the list that drops down (there
should only be one function name in the list at this point).
7. Double-click on the value ButtonClick. You are presented with the Code Editor
with the cursor in the ButtonClick() function. Modify the code so that it reads like
this:
void __fastcall TPMEForm::ButtonClick(TObject *Sender)
{
if (Sender == Hide) Memo->Hide();
else Memo->Show();
}
8. Bake at 425 degrees for 1 hour or until golden brown. (Just making sure you’re still
awake.)
Right now your form should look similar to Figure 5.4. Compile and run the program. Click
each of the buttons to be sure that they do as advertised.
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