ch07.htm

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predefined colors or to create your own colors by clicking the Define Custom Colors
button. Figure 7.1 shows the Color dialog box after the Define Custom Colors button
has been clicked.</P>
<P><A HREF="javascript:popUp('28670701.gif')"><B>FIGURE 7.1.</B></A><B> </B><I>The
Color dialog box.</I></P>
<P><strong>NOTE:</strong> This is the same Color dialog box that will be displayed if you
implement the ColorDialog component in your application.</P>
<P>If you choose a color from the Color dialog box, you see that the value of the
Color property changes to a hexadecimal string. This string represents the red, green,
and blue (RGB) values that make up the color. If you know the exact RGB value of
a color, you can type it in (not likely!).</P>
<P>Most of the time you will probably choose a color from the list of color values
provided. When you click the drop-down button to display the list of possible values,
you will see what essentially amounts to two groups of values. The first group of
colors begins with clBlack and ends with clWhite. These are the Delphi predefined
colors; this list represents the most commonly used colors. To choose one of the
listed colors, simply click the color in the list. If you can't find a color in the
list that suits your needs, you can invoke the Color dialog box as discussed.</P>
<P>The second group of colors in the list begins with clScrollBar. This group of
colors represents the Windows system colors. If you use colors from this list, your
application will automatically adjust its colors when the user changes color schemes
in Windows. If you want your application to follow the color scheme the user has
chosen for his or her system, you should choose colors from this list rather than
from the first list.</P>
<P>Use of color should be carefully considered. Proper use of color provides an aesthetically
pleasing environment for the user. Abuse of colors makes for an obnoxious application
that is annoying to use. Color is like a magnet to new programmers. It is common
to want to throw lots of colors on a form because it's fun and easy, but don't get
caught up in the fun at the expense of your users.</P>
<P>
<H3><A NAME="Heading8"></A>The Cursor Property</H3>
<P>The Cursor property controls the cursor that is displayed when the user moves
the mouse cursor over the component. Windows automatically changes cursors for some
components. For example, Windows changes the cursor to an I-beam when the cursor
is moved over an Edit, Memo, or RichEdit component.</P>
<P>To let Windows manage the cursor, leave the Cursor property set to crDefault.
If you have specialized windows (components), you can specify one of the other cursors.
When the mouse is moved over that component, Windows will change the cursor to the
one you specified.</P>
<P>Frequently, you will need to change cursors at runtime. A long process, for example,
should be indicated to the user by displaying the hourglass cursor. When you reset
the cursor, you need to be sure to set the cursor back to whatever it was originally.
The following code snippet illustrates this concept:</P>
<P>
<PRE>var
  OldCursor : TCursor;
begin
  OldCursor := Screen.Cursor;
  Screen.Cursor := crHourGlass;
  { do some stuff which takes a long time }
  Screen.Cursor := OldCursor;
end;
</PRE>
<P>This ensures that the cursor that was originally set for the application is properly
restored.</P>
<P>Another cursor property, DragCursor, is used to set the cursor that is used when
the mouse cursor is over a component that supports drag-and-drop. As with colors,
you should be prudent in your use of cursors. Use custom cursors when needed, but
don't overdo it.</P>
<P>
<H3><A NAME="Heading9"></A>The Enabled Property</H3>
<P>Components can be enabled or disabled through the Enabled property. When a component
is disabled, it cannot accept focus (clicking on it has no effect), and usually it
gives some visual cue to indicate that it is disabled. In the case of buttons, for
example, the button text is grayed out as is any bitmap on the button. Enabled is
a Boolean property: Set it to True to enable the component or set it to False to
disable the component. Enabling and disabling windows (remember that windowed components
are windows, too) is a feature of Windows itself.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> Some components show their disabled state at design time, but most
	don't. The BitBtn component is one that does show its disabled state at design time.
	
<HR>


</BLOCKQUOTE>

<P>The Enabled property applies mostly to windowed components, but it can apply to
non-windowed components as well. The SpeedButton component is an example of a non-windowed
component that can be disabled.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> Modifying the Enabled property for a Panel component has additional
	implications. Panels are often used as containers for other controls. Therefore,
	a panel becomes the parent of the controls that are placed on the panel. If you disable
	a panel, the components on the panel will not show as disabled, but they will not
	function because their parent (the panel) is disabled. 
<HR>


</BLOCKQUOTE>

<P>Although components can be disabled at design time, enabling and disabling components
is something that is usually done at runtime. Menu items, for example, 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.</P>
<P>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:</P>
<P>
<PRE>if CanSave then
  FileSave.Enabled := True
else 
  FileSave.Enabled := False;
</PRE>
<P>This process is often referred to as <I>command enabling</I> and is an important
part of a professional-looking Windows program.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>TIP:</strong> The TActionList component can be used to enable or disable a component
	or groups of components. TActionList is discussed in detail on Day 13, &quot;Beyond
	the Basics,&quot; in the section &quot;Command Enabling.&quot; 
<HR>


</BLOCKQUOTE>

<P>
<H3><A NAME="Heading10"></A>The Font Property</H3>
<P>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 this chapter in the section
&quot;The Font Dialog Box.&quot;) Figure 7.2 shows the Object Inspector with the
Font property node expanded to reveal the TFont properties.</P>
<P><A HREF="javascript:popUp('28670702.gif')"><B>FIGURE 7.2.</B></A><B> </B><I>The
Object Inspector showing the Font property.</I></P>
<P>The Color property sets the color of the font, and the Name property enables you
to choose the typeface for the font.</P>
<P>The Height and Size properties of TFont deserve special mention as well:</P>

<UL>
	<LI>The Height property is used to specify the height of the font in pixels.
	<P>
	<LI>The Size property is used to specify the height of the font in points.
</UL>

<P>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.</P>
<P>The Pitch property is not particularly useful. I'll explain it in just a moment,
but first a quick tutorial on fonts. A font can be either proportionally spaced or
fixed space:</P>

<UL>
	<LI>Most fonts are <I>proportionally spaced</I>, which means that each letter only
	takes as much space as needed. For example, an uppercase M takes up much more space
	than a lowercase i. Take a look at the letters in this book and you will see what
	I mean. Examples of proportional fonts include Times New Roman, Arial, and Bookman.
	<P>
	<LI>With a <I>fixed space </I>font (typically called a fixed-pitch font), on the
	other hand, all characters take exactly the same amount of space. This is convenient
	for windows such as code editors (the Delphi Code Editor, for example) or any other
	window where a fixed-pitch font is desired. Courier New is probably the most commonly
	used fixed-pitch font, although Fixedsys is the Windows fixed-pitch font of choice
	in some Windows applications. <I>Fixed space </I>fonts are harder to read, so they
	aren't normally used for long blocks of text other than code.
</UL>

<P>In theory, the Pitch property can be used to force a proportionally spaced font
to fixed space and vice versa. The problem is that Windows might perform font substitutions
to carry out the conversion. In other words, you really don't know what you might
get. It is far better to pick exactly the font you require than to rely on the Pitch
property.</P>
<PRE></PRE>
<P>Finally, the Style property of TFont can be used to toggle bold, italic, underline,
or strikethrough. These styles are not mutually exclusive, so you can mix styles
in any way you choose.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>TIP:</strong> Although you can use the Object Inspector to change font properties,
	the Font dialog box (invoked when you click the ellipsis button next to the Font
	property) has the added benefit of showing you a sample of what the font looks like
	as you choose different font options. To simply change the font's Style property
	or Size property, use the Object Inspector. But if you are looking for just the right
	font, the Font dialog box is a better choice. 
<HR>


</BLOCKQUOTE>

<H3></H3>
<H3><A NAME="Heading11"></A>The Hint Property</H3>
<P>The Hint property is used to set hint text for a component. The hint text has
two parts. The first part is sometimes called the <I>short hint</I>. This is the
hint text that is displayed when the user places the cursor over the component and
pauses. The pop-up window that displays the hint text is called a <I>tooltip</I>.</P>
<P>The second part of the hint text is sometimes called the <I>long hint</I>. The
long hint is the optional hint text that shows in the status bar when the user moves
the mouse cursor over the component. The short and long hint texts are separated
by a pipe (|). For example, to specify both the short hint text and the long hint
text for a File Open speed button, you would enter the following for the Hint property:</P>
<P>
<PRE>File Open|Open a file for editing
</PRE>
<P>In order for short hints to show, you must have the Application object's ShowHint
property set to True (the default) as well as the component's ShowHint property.
Displaying the long hint in the status bar requires a little more work, so I'll save
that discussion for tomorrow.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> You can specify the short hint text, the long hint text, or both.
	You can use the pipe to tell Delphi which hint text you are supplying. If you don't
	use the pipe, both the short hint and the long hint will use the same text. 
<HR>
</P>
	<P>
<HR>
<strong>NOTE:</strong> Although there are no limits on the length of either the long hint
	or the short hint, you should keep each hint's use in mind when you create them.
	Short hints should probably be limited to 30 characters or fewer. Long hints can
	be more descriptive, but keep in mind that long hints that are very long will be
	truncated when displayed in the status bar. 
<HR>


</BLOCKQUOTE>

<H3></H3>
<H3><A NAME="Heading12"></A>The ParentColor, ParentCtl3D, ParentFont, and ParentShowHint
Properties</H3>
<P>The ParentColor, ParentCtl3D, ParentFont, and ParentShowHint properties work the
same way, so I'll discuss them at the same time. When these properties are set to
True, the component takes its Color, Ctl3D, Font, or ShowHint settings from its parent.
For example, for most components the ParentFont property is set to True by default.
This means the component will inherit the font that its parent is currently using.
To better understand this, do this exercise:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Create a blank form. Set the Font property's Size property to 16.
	<P>
	<DT></DT>
	<DD><B>2. </B>Place a Label component on the form. Notice that the label automatically
	uses the 16-point font.
	<P>
	<DT></DT>
	<DD><B>3. </B>Place a Button component on the form. It also uses the 16-point font.
	<P>
</DL>

<P>You can set this property to False, but by the time the component is placed it
is already too late and you will have to change the font manually to the font you
want for the component.</P>
<P>
<H3><A NAME="Heading13"></A>The Tag Property</H3>
<P>The Tag property is nothing more than a four-byte variable set aside for your
use. You can use the Tag property to store any data that your component might need.
The data stored might be a pointer to another class, an index value, or any number
of other possibilities. Using the Tag property would probably be considered an advanced
programming technique.</P>
<P>
<H3><A NAME="Heading14"></A>Other Common Properties</H3>
<P>Table 7.1 lists other common properties that are frequently used. These properties
don't require as much explanation, so they are listed here for your reference. Not
all components have each of the properties listed.</P>
<P>
<H4>TABLE 7.1. ADDITIONAL COMPONENT PROPERTIES.</H4>
<P>
<TABLE BORDER="1">
	<TR ALIGN="LEFT" VALIGN="TOP">
		<TD ALIGN="LEFT"><I>Property</I></TD>
		<TD ALIGN="LEFT"><I>Description</I></TD>
	</TR>
	<TR ALIGN="LEFT" VALIGN="TOP">
		<TD ALIGN="LEFT">BorderStyle</TD>
		<TD ALIGN="LEFT">Can be bsSingle or bsNone. Use bsNone when you want the component to blend in with
			the background.</TD>
	</TR>
	<TR ALIGN="LEFT" VALIGN="TOP">