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278 Day 8
NOTE
Modifying the Enabled property for a panel component has additional
implications. Panels are often used as containers for other controls.
Therefore, they become the parents of the controls that are placed
within them. If you disable a panel, the components on the panel will
not show as disabled, but will not function because their parent (the
panel) is disabled.
Although components can be disabled at design time, enabling and disabling components
is something that is usually done at runtime. Menu items, for instance, should be enabled or
disabled according to whether they apply at a given time. The same is true of buttons. There
are a variety of reasons why you might want to disable other types of controls as well.
To disable a component at runtime, just assign false to its Enabled property, and to enable
a component assign true to Enabled. The following code snippet enables or disables a menu
item based on some condition:
if (saveEnabled) FileSave->Enabled = true;
else FileSave->Enabled = false;
This process is often referred to as command enabling and is an important part of a
professional-looking Windows program.
The Font Property
The Font property is a major property and therefore needs to be included here, but there is
not a lot that needs to be said about it. The Font property is an instance of the TFont class,
and as such has its own properties. You can set the Font properties by double-clicking on the
font name in the Object Inspector (which will expand the Font node and show the Font
properties) or by invoking the Font dialog box. (The Font dialog box is discussed in more
detail later in the chapter in the section “The Font Dialog Box.”) Figure 8.2 shows the Object
Inspector with the Font property node expanded to reveal the TFont properties.
The Color property sets the color of the font, and the Name property allows you to choose the
typeface for the font.
The Height and Size properties of TFont deserve special mention. The Height property is used
to specify the height of the font in pixels, whereas the Size property is used to specify the
height of the font in points. When you change one of these properties, the other will change
automatically. The Height is often specified as a negative number. Refer to the online help
for TFont for an explanation of why this is the case.