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VCL Components
property set to true. However, when the user presses Enter on the
keyboard, the first button in the tab order that has its Default property
set to true will be invoked. Similarly, when the user presses the Esc key
to close the form, the return value from ShowModal() will be the
ModalResult value of the first button in the tab order that has its Cancel
property set to true.
The Enabled Property
Earlier I discussed the Enabled property when I discussed components in general. This
property is used a lot with buttons to enable or disable the button depending on the current
state of the program or of a particular form. When a button is disabled (its Enabled property
is set to false), its text is grayed out, and the button does not function. In the case of buttons
with bitmaps on them (BitBtn and SpeedButton), the bitmap will also be grayed out
automatically.
Button components have only one method of interest: the Click() method, which simulates
a mouse click. When you call Click() for a button, the OnClick event of the button is executed
just as if the user had clicked the button. As for events, typically only the OnClick event is used.
Now let’s take a look at the different button components C++Builder provides.
The Button Component
The standard Button component is sort of like actor Danny DeVito—he ain’t pretty, but he
sure gets a lot of work. There really isn’t anything to add concerning the standard Button
component. It has a default Height property value of 25 pixels and a default Width property
value of 75. Typically you will place a button on a form and respond to its OnClick event, and
that’s about it.
The BitBtn Component
The BitBtn component is a perfect example of how a component can be extended to provide
additional functionality. In this case the standard Button component is extended to allow a
bitmap to be displayed on the face of the button.
The BitBtn component has several properties over what the Button component provides. All
these properties work together to manage the bitmap on the button and the layout between
the bitmap and the button’s text. They are explained in the following sections.
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