ch05.htm

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All of the controls (the toolbar button and the menu items) can be enabled or disabled
at one time using the TActionList component.</P>
<P><B>Components on the Additional Tab&#160;&#160;</B>Delphi has another group of
components that I'll throw in with the standard controls. These controls can be found
under the Additional tab on the Component palette. The classes representing these
components include TBitBtn, TSpeedButton, TMaskEdit, TStringGrid, TDrawGrid, TImage,
TShape, TBevel, TScrollBox, TCheckListBox, TSplitter, TStaticText, and TChart. The
TBitBtn class represents a button that has an image on it.</P>
<P>
<P>TSpeedButton is also a button with an image, but this component is not a true
button. Instead, it's a graphical depiction of a button. This enables you to have
a large number of speed buttons and not consume Windows resources for each button.</P>
<PRE></PRE>
<P>The TImage component enables you to place an image on a form that can then be
selected from a file on disk. You can use the TBevel component to create boxes and
lines that are raised (bumps) or lowered (dips). Bevels can be used to divide a form
into visual regions and to provide an aesthetically pleasing form. The TStringGrid
and TDrawGrid classes give you a means to present information in a grid format.</P>
<P>
<H4>Win32 Custom Control Classes</H4>
<P>VCL has component classes that encapsulate many of the Windows 32-bit custom controls.
These classes include TListView, TTreeView, TTrackBar, TProgressBar, TTabControl,
TPageControl, TRichEdit, TImageList, TStatusBar, TAnimate, TDateTimePicker, TToolBar,
TCoolBar, and a few others. Some of these controls are, by nature, complicated, and
the VCL classes that represent them are complicated as well. Trust me when I say
that VCL does much to ease the burden of working with these common controls. You
have to spend some time with these classes before you fully understand them. I cover
the TToolBar, TCoolBar, TImageList, and TStatusBar components on Day 13, &quot;Beyond
the Basics.&quot;</P>
<P>
<H4>Database Component Classes</H4>
<P>VCL has a host of database components that include both visual and nonvisual classes.
Nonvisual database components include TDataSource, TDatabase, TTable, and TQuery.
These classes encapsulate behind-the-scenes database operations.</P>
<P>Visual database component classes are the part of the VCL database operations
that users see and interact with. For instance, a TDBGrid component is used to display
a database table in grid format. In this way, the TDBGrid acts as the interface between
the user and the database. Through the TDBGrid, the user can view and edit the database
table on disk.</P>
<P>The TDBNavigator component provides buttons that enable the user to move through
a database table. This class includes buttons for next record, previous record, first
record, last record, cancel edit, accept edit, and undo edit.</P>
<P>Other data-aware component classes hook standard Windows controls to database
fields. These classes include TDBText, TDBEdit, TDBListBox, and TDBImage, among others.</P>
<P>A group of components usually associated with database programming is the QuickReport
components. This group of components makes report writing easy, especially if your
data source is a database. The database QuickReport components are discussed on Days
16, 17, and 18.</P>
<P>
<H4>Common Dialog Classes</H4>
<P>As you are no doubt aware, Windows has common dialog boxes for things like opening
files, saving files, choosing fonts, and choosing colors. VCL encapsulates these
common dialog boxes in classes representing each type. The classes are TOpenDialog,
TSaveDialog, TOpenPictureDialog, TSavePictureDialog, TFontDialog, TColorDialog, TPrintDialog,
and TPrinterSetupDialog. VCL also adds the TFindDialog and TReplaceDialog classes
to this component group. All the components in this group are nonvisual in that they
don't have a design-time visual interface. The dialog boxes are visible when displayed
at runtime, of course.</P>
<P>
<H4>System Component Classes</H4>
<PRE>The System tab on the Component palette contains a mixture of visual and nonvisual components. The TTimer class is used to represent a Windows system timer. Its single event is OnTimer, which is called each time the timer fires. The timer 
interval is set through the Interval property. TTimer is a nonvisual component.
</PRE>
<P>Tucked into this group of classes is the TMediaPlayer class. This class enables
you to play media files like wave audio, AVI video, and MIDI audio. The media can
be played, stopped, paused, or positioned at a particular point in the file, as well
as many other operations. This class has many properties and events that greatly
simplify the complex world of the Windows Media Control Interface (MCI).</P>
<P>The TPaintBox component gives you an empty canvas on which you can draw anything
you like. This component has many potential uses. The System group includes OLE and
dynamic data exchange (DDE) classes as well.</P>
<P>
<H4>The Win 3.1 Group of Components</H4>
<P>Don't make the mistake of automatically discarding this component group just because
of the name of the tab on which it resides. This group contains some great components.
(The Win 3.1 tab has its roots in Delphi 1.) In particular, I like the TTabSet and
TNotebook components. This group also includes several component classes that enable
you to build your own custom File Open or File Save dialog box. The classes are TFileListBox,
TDirectoryListBox, TDriveComboBox, and TFilterComboBox.</P>
<P>
<H4>Internet Components</H4>
<P>Depending on which version of Delphi you have (Standard, Professional, or Client/Server),
you might have an Internet tab. This tab contains components used in Internet programming.
The components include HTML, FTP, SMTP, POP3, and HTTP components. It also contains
components that are for general network programming via the Winsock API. Most of
these components are native VCL components, although at least one, the THTML component,
is an ActiveX control.</P>
<P>
<H4>Sample Components</H4>
<P>The Samples tab contains components that can be used to gain an understanding
of how to write components. The source for these components is provided so that you
can see how they work. The sample components include TGauge, TColorButton, TSpinButton,
TSpinEdit, TDirectoryOutline, and TCalendar.</P>
<P>
<H4>ActiveX Controls</H4>
<PRE>The ActiveX tab contains ActiveX controls that you can use in your applications. These controls include Chart FX by Software FX, Inc., Visual Speller by Visual Components, Inc., Formula One Spreadsheet, Formula One VtChart, and a Graph control by 
Bits Per Second, Ltd.
</PRE>
<H4>GDI Classes</H4>
<P>The GDI (graphics device interface) classes get a lot of work in Windows GUI applications.
These classes encapsulate the use of bitmaps, fonts, device contexts (DCs), brushes,
and pens. It is through these GDI objects that graphics and text are displayed on
a window. The GDI classes are not associated with a specific component, but many
components have instances of these classes as properties. For example, an edit control
has a property called Font that is an instance of the TFont class.</P>
<P>The term <I>device context</I> is well known by traditional Windows programmers.
In VCL, though, the term is not widely used. This is because VCL encapsulates Windows
DCs in the TCanvas class. VCL uses the term <I>canvas</I> to refer to a Windows device
context. A canvas provides a surface that you can draw on using methods like MoveTo,
LineTo, and TextOut. Bitmaps can be displayed on the canvas using the Draw or StretchDraw
methods. The concept of a canvas that you draw on makes more sense than the archaic
term <I>device</I> <I>context</I>, don't you think? Graphics operations are discussed
on Day 12, &quot;Graphics and Multimedia Programming.&quot; The following is a list
of the more common GDI classes used:</P>

<UL>
	<LI>The TCanvas class contains instances of the other GDI classes. For example, when
	you do a MoveTo/LineTo sequence, a line is drawn with the current pen color. The
	Pen property is used to determine the current pen color and is an instance of the
	TPen class. TPen has properties that determine what type of line to draw: the line
	width, the line style (solid, dashed, dotted, and so on), and the mode with which
	to draw the line.
	<P>
	<LI>The TBrush class represents a brush used as the fill pattern for canvas operations
	like FillRect, Polygon, and Ellipse. TBrush properties include Color, Style, and
	Bitmap. The Style property enables you to set a hatch pattern for the brush. The
	Bitmap property enables you to specify a bitmap for the fill pattern.
	<P>
	<LI>TBitmap encapsulates bitmap operations in VCL. Properties include Palette, Height,
	Width, and TransparentColor. Methods include LoadFromFile, LoadFromResourceID, and
	SaveToFile. TBitmap is used by other component classes such as TImage, TBitBtn, and
	TSpeedButton in addition to TCanvas. An instance of the TBitmap class can also be
	used as an offscreen bitmap. Offscreen bitmaps are commonly used in graphics-intensive
	applications to reduce flicker and improve graphics performance.
	<P>
	<LI>The TFont class handles font operations. Properties include Color, Height, and
	Style (bold, italic, normal, and so on). The TFont class is used by all component
	classes that display text.
</UL>

<P>In addition to the GDI classes listed here, there are others that either work
as helper classes or extend a base class to provide extra functionality. As you work
with Delphi, you will learn more about these classes and how to use them. Figure
5.6 shows the hierarchy of the VCL classes that encapsulate GDI operations.</P>
<P><A HREF="javascript:popUp('28670506.gif')"><B>FIGURE 5.6.</B></A><B> </B><I>VCL
GDI class hierarchy.</I></P>
<P>
<H4>Utility Classes</H4>
<P>VCL contains many utility classes that you can use in your applications. A <I>utility</I>
<I>class</I> simplifies some task in Windows programming. For instance, the TIniFile
class eases the use of writing and reading Windows configuration files (.INI files).
Conventional wisdom has it that the use of .INI files is out and the Registry is
in. To aid in Registry operations, VCL has the TRegistry and TRegkeyInfo classes.</P>
<P>The TStringList class enables arrays of strings. TStringList is used by many of
the component classes to store strings. For instance, the TMemo class uses a TStringList
object for its Lines property. TStringList has the capability to save its list of
strings to file or load strings from a file using the LoadFromFile and SaveToFile
methods. TStringList can also be used to read and write text files.</P>
<P>Another useful VCL utility class is the TList class. This class enables you to
create arrays of any type of object you want. The TList class simply stores a list
of pointers. The main advantage of the TList class is that it provides you with an
array that will dynamically grow or shrink as new objects are added or removed.</P>
<P>VCL also includes a set of classes to enable reading and writing of streams (a
stream is really just a block of data). The TStream, TFileStream, TMemoryStream,
and TResourceStream classes all enable you to read or write data to streams. TStream
is the base class for all stream classes. The TFileStream class is used when dealing
with files on disk, TMemoryStream is used to manipulate data in memory, and TResourceStream
is used to load binary resources from EXEs and DLLs. These classes are for more advanced
uses, but they are invaluable when you need the particular functionality they provide.
For more information on these classes, see the Delphi VCL Help.</P>
<P>
<H3><A NAME="Heading11"></A>And That's Not All . . .</H3>
<P>By no means did I cover all the VCL classes here. I did, however, touch on those
classes that you are most likely to use in your applications.</P>
<P>Flip back a few pages and take another look at Listing 5.1. I showed you how easy
it was to load and display a bitmap with Delphi. Let's do an exercise that proves
the point. First, begin a new application. You will be looking at a blank form. Perform
the following steps:</P>

<DL>
	<DD><B>1. </B>Change the Caption property of the form to Bitmap Test Program.
	<DT></DT>
	<DD><B>2. </B>Click on the Additional tab on the Component palette, choose the Image
	component, and place the component on the form.
	<P>
	<DT></DT>
	<DD><B>3. </B>Locate the Align property and change it to alClient. The picture component
	fills the client area of the form.
	<P>
	<DT></DT>
	<DD><B>4. </B>Locate the Stretch property and change it to True.
	<P>
	<DT></DT>
	<DD><B>5. </B>Locate the Picture property and double-click the Value column.
	<P>
	<DT></DT>
	<DD><B>6. </B>The Picture Editor dialog box is displayed. Click the Load button.
	The File Open dialog box is displayed.
	<P>
	<DT></DT>
	<DD><B>7. </B>Navigate to the \Program Files\Common Files\Borland Shared Files\Images\Splash\256Color
	directory and choose an image from those presented (I like HANDSHAKE.BMP). Click
	OK.
	<P>
	<DT></DT>
	<DD><B>8. </B>You are now back to the Image Editor dialog box, and the bitmap you
	chose is displayed in the preview window. Click OK. (If you want to choose a different
	bitmap, click the Load button again.) The bitmap now fills the client area of the
	form.
	<P>
	<DT></DT>
	<DD><B>9. </B>Click the Run button. When the application runs, you can size the window
	and the bitmap will always fill the client area of the window.
	<P>
</DL>

<P>See how easy it is? It would have been even easier if you hadn't bothered to make
the image fill the form's client area. Figure 5.7 shows the bitmap test program running.</P>
<P><A HREF="javascript:popUp('28670507.gif')"><B>FIGURE 5.7.</B></A><B> </B><I>The
bitmap test program running.</I>
<H2><A NAME="Heading12"></A>Summary</H2>
<P>Today you learned about frameworks and how VCL fits into the framework scene.
I discussed properties, methods, and events and gave you some hands-on experience
in the process. You finished today with an overview of the VCL classes that you are
likely to encounter when programming in Delphi. I didn't cover them all, but I gave
you a brief look at the most commonly used classes.</P>
<P>So where is this industry going? The wave of the future appears to be components.
The great thing about VCL is that if you decide (or are forced) to switch to C++,
you can still use VCL. You might be surprised to learn that the very same VCL that
is used in Delphi is also used in Borland C++Builder. Any time you spend learning
VCL can be immediately applied to C++ if the time ever comes. It's the same VCL,
so there's nothing to relearn.</P>
<P>
<H2><A NAME="Heading13"></A>Workshop</H2>
<P>The Workshop contains quiz questions to help you solidify your understanding of
the material covered and exercises to provide you with experience in using what you
have learned. You can find the answers to quiz questions in Appendix A, &quot;Answers
to the Quiz Questions.&quot;</P>
<P>
<H3><A NAME="Heading14"></A>Q&amp;A</H3>

<DL>
	<DT></DT>
	<DD><B>Q What is a framework?</B>
	<P>
	<DT></DT>
	<DD><B>A</B> A framework, also called a class library, is a set of classes that simplifies
	Windows programming. A good framework implements object-oriented design and object-oriented
	programming to apply an object-oriented approach to writing Windows applications.
	<P>
	<DT></DT>
	<DD><B>Q Is VCL a framework?</B>
	<P>
	<DD><B>A</B> Yes, VCL is a framework. VCL is written in Object Pascal and works with
	both Delphi and C++Builder.
	<DT></DT>
	<DD><B>Q It seems as though the component way of doing t