ch04.htm

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	<DD><B>4. </B>Click the Load button. In the File Open dialog box, navigate to the
	\Borland Shared Files\Images\Icons directory and choose an icon from the icon files
	listed. Click Open. The icon you selected is displayed in the Picture Editor window.
	Click OK to close the Picture Editor. The icon is displayed on the form. Note that
	the Image component has sized itself to the size of the icon.
	<P>
	<DT></DT>
	<DD><B>5. </B>Position the icon as desired.
	<P>
</DL>

<P>At this point you need an OK button on the form. Let's branch out a little and
take a look at a new component:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>If you're not already there, click the Additional tab on the Component
	palette. Select the BitBtn component and place a BitBtn on the form near the bottom
	and center it horizontally.
	<P>
	<DT></DT>
	<DD><B>2. </B>Locate the Kind property and change it to bkOK. Notice that a green
	check mark has appeared on the button and the Caption property has changed to OK.
	That's all you have to do with the button. The BitBtn component already includes
	code to close the form when the OK button is clicked.
	<P>
</DL>

<P>Let's add one final touch to the About box:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Locate the Bevel button (on the Additional tab in the Component palette)
	and click it.
	<P>
	<DT></DT>
	<DD><B>2. </B>Move to the form, but rather than clicking on it, drag a box around
	the three text labels. The Bevel component appears when you stop dragging. If you
	didn't get it quite right, you can resize or reposition the component.
	<P>
	<DT></DT>
	<DD><B>3. </B>Locate the Shape property and change it to bsFrame. You now have a
	3D frame around the static text.
	<P>
</DL>

<P>Your form should now look something like the one shown in Figure 4.12. Save the
unit (File | Save) and give it the name About.</P>
<P><A HREF="javascript:popUp('28670412.gif')"><B>FIGURE 4.12.</B></A><B> </B><I>The
finished About box.</I></P>
<P>Are you ready to compile and run the program? Not yet. You need to add the About
unit to the main form's uses list. Perform these steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Switch to the Code Editor (press F12) and select the Main.pas tab.
	<P>
	<DT></DT>
	<DD><B>2. </B>Choose File | Use Unit from the main menu.
	<P>
	<DT></DT>
	<DD><B>3. </B>Choose the About unit from the Use Unit dialog box and click OK.
	<P>
</DL>

<P>Now you're ready to run the program, so click the Run button. When the program
runs, click the About button, and the About dialog box is displayed. Note that the
dialog box is modal (you can't go back to the main window while the dialog box is
displayed) and that it cannot be sized. The About form behaves in every way like
a regular Windows dialog box.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> The common dialog box classes (TOpenDialog, TSaveDialog, TFontDialog,
	and so on) do not represent dialog boxes created as Delphi forms. Windows provides
	these dialog boxes as a set of common dialog boxes that all Windows applications
	can use (the actual dialog boxes are contained in a file called COMDLG32.DLL). The
	VCL dialog box classes encapsulate the common dialog boxes to make using them easier.
	<I>Encapsulate</I> in this sense means to take a common dialog box's functionality
	and roll it into a VCL component. The component makes it much easier to use the dialog
	box than it would otherwise be. 
<HR>
</P>
	<P>
<HR>
<strong>NOTE:</strong> Delphi includes several prebuilt forms that you can choose from to
	help you build dialog boxes as quickly as possible. I'll discuss those on Day 8.
	
<HR>


</BLOCKQUOTE>

<P>
<H3><A NAME="Heading18"></A>Secondary Windows Versus Dialog Boxes</H3>
<P>A <I>secondary window</I> is a form that you display from your main window. So
when is a form a secondary window and when it is a dialog box? When it really comes
down to it, there is no difference between a secondary window and a dialog box in
Delphi. You might have windows that resemble dialog boxes, and you might have other
windows that resemble a traditional window.</P>
<P>In the grand scheme of things, they all are forms and it doesn't make much sense
to differentiate between the terms <I>dialog box</I> and <I>secondary form</I>. It's
all the same in the end. In traditional programming environments, you have to specifically
create a dialog box or specifically create a secondary window in an application.
Delphi frees you from that restriction and enables you to treat both dialog boxes
and windows exactly the same.</P>
<P>
<H3><A NAME="Heading19"></A>The Multiple Document Interface Model</H3>
<P>So far, you have built only single document interface (SDI) applications. An <I>SDI
application</I> has a single main window and typically displays dialog boxes as needed,
but does not otherwise display child windows.</P>
<P><strong>New Term:</strong> Some programs follow the multiple document interface (MDI)
model. <I>MDI applications</I> consist of a main window (the MDI parent) and child
windows (the MDI children).</P>
<P>Examples of programs that use the MDI model are the Windows System Configuration
Editor (SYSEDIT) and the Windows 3.1 Program Manager.</P>
<P>One of the most obvious characteristics of the MDI model is that the MDI child
windows are confined to the parent. You can drag the child windows within the parent
window, but you cannot drag them outside the parent. MDI applications almost always
have a Window item on their main menu. This menu usually contains items named Cascade
and Tile, which enable you to display the MDI child windows in either a cascaded
or tiled arrangement. When an MDI child is minimized, its icon is contained within
the MDI parent's frame. When a regular (non-MDI) child window is minimized, its icon
is placed on the Windows desktop.</P>
<P>To create an MDI application in Delphi, you must set the main form's FormStyle
property to fsMDIForm. Each of the MDI child windows must have the FormStyle property
set to fsMDIChild. Aside from that restriction, there is very little to creating
an MDI application in Delphi. You simply create the main window form and one or more
forms to be used as child windows, and you're off and running.</P>
<P>
<H3><A NAME="Heading20"></A>Key Properties for Forms</H3>
<P>The TForm class has a lot of properties. Some of these properties are obscure
and rarely used; others are widely used. I'll touch on the most widely used properties
here. I won't include obvious properties such as Caption, Color, Left, Top, Width,
and Height unless they have a particular feature you should be aware of.</P>
<P>
<H4>Design-Time Properties</H4>
<P>The properties outlined in this section can be set at design time and also at
runtime. Almost all these properties can be read at runtime as well.</P>
<P><B>ActiveControl&#160;&#160;</B>The ActiveControl property is used to set the
control that will have focus when the form is activated. For example, you might want
a particular edit control to have focus when a dialog box form is displayed. At design
time, the Value column for the ActiveControl property contains a list of components
on the form. You can choose one of the components from this list to make that component
the active control when the form is first displayed.</P>
<P><B>AutoScroll, HorzScrollBar, and VertScrollBar&#160;&#160;</B>Together, the AutoScroll,
HorzScrollBar, and VertScrollBar properties control the scrollbars for a form. If
AutoScroll is set to True (the default), scrollbars automatically appear when the
form is too small to display all its components. The HorzScrollBar and VertScrollBar
properties each have several properties of their own that control the scrollbar operations.</P>
<P><B>BorderIcons&#160;&#160;</B>The BorderIcons property controls which system buttons
will appear on the form at runtime. Choices include the system menu, the minimize
button, the maximize button, and the help button.</P>
<P><B>BorderStyle&#160;&#160;</B>The BorderStyle property indicates what type of
border the form will have. The default value is bsSizeable, which creates a window
that can be sized. Non-sizable styles include bsDialog and bsNone.</P>
<P><B>ClientWidth and ClientHeight&#160;&#160;</B>You can specify the client area
width and height rather than the full form's width and height by using the ClientWidth
and ClientHeight properties. (The <I>client area</I> of the form is the area inside
of the borders and below the title bar and menu bar.) Use these properties when you
want the client area to be a specific size and the rest of the window to adjust as
necessary. Setting the ClientWidth and ClientHeight properties makes automatic changes
to the Width and Height properties.</P>
<P><B>Constraints&#160;&#160;</B>The Constraints property is used to set the maximum
and minimum width and height of the form. Simply set the MaxHeight, MaxWidth, MinHeight,
and MinWidth values as desired and the form will conform to those constraints.</P>
<P><B>DefaultMonitor&#160;&#160;</B>The DefaultMonitor property determines which
monitor the form will appear on in a multimonitor environment (such as Windows 98).</P>
<P><B>DockSite&#160;&#160;</B>The DockSite property determines whether the form will
act as a dock site for dockable components. Dock sites and dockable components are
discussed on Day 13, &quot;Beyond the Basics.&quot;</P>
<P><B>Font&#160;&#160;</B>The Font property specifies the font that the form uses.
The important issue to understand here is that the form's font is inherited by any
components placed on the form. This also means that you can change the font used
by all components at one time by changing just the form's font. If an individual
control's font has been manually changed, that control's font will not be changed
when the main form's font changes.</P>
<P><B>FormStyle&#160;&#160;</B>This property is usually set to fsNormal. If you want
a form to always be on top, use the fsStayOnTop style. MDI forms should use the fsMDIForm
style and MDI child forms should use the fsMDIChild style. MDI forms and MDI child
windows were discussed earlier in this chapter in the section &quot;The Multiple
Document Interface Model.&quot;</P>
<P><B>HelpContext and HelpFile&#160;&#160;</B>The HelpContext property is used to
set the help context ID for a form. If context help is enabled for a form, the Windows
Help system will activate when the F1 key is pressed. The context ID is used to tell
the Help system which page in the help file to display. The HelpFile property is
the name of the help file that will be used when F1 is pressed.</P>
<P><B>Icon&#160;&#160;</B>The Icon property sets the icon that is used on the title
bar for the form when the form is displayed at runtime and also when the form is
minimized. In some cases, setting this property has no effect. For example, when
the FormStyle is set to fsDialog, the Icon property is ignored.</P>
<P><B>KeyPreview&#160;&#160;</B>When KeyPreview is True, the form's OnKeyPress and
OnKeyDown events will be generated when a key is pressed in any component on the
form. Ordinarily, forms don't receive keyboard events when a component on the form
has focus.</P>
<P><B>Position&#160;&#160;</B>The Position property determines the size and position
of the form when the form is initially displayed. The three basic choices are poDesigned,
poDefault, and poScreenCenter:</P>

<UL>
	<LI>poDesigned causes the form to be displayed in the exact position it was in when
	it was designed.
	<P>
	<LI>poDefault enables Windows to set the size and position according to the usual
	Windows Z-ordering algorithm. (Z-ordering is what Windows uses to decide where it
	displays a new window on the screen. If the new window does not have specific placement
	information, it will be displayed just below and to the right of the last window
	displayed on the screen.)
	<P>
	<LI>The poScreenCenter option causes the form to be displayed in the center of the
	screen each time it is shown.
</UL>

<P><B>Visible&#160;&#160;</B>The Visible property controls whether the form is initially
visible. This property is not particularly useful at design time, but at runtime
it can be read to determine whether the form is currently visible. It can also be
used to hide or display the form.</P>
<P><B>WindowState&#160;&#160;</B>The WindowState property can be read to determine
the form's current state (maximized, minimized, or normal). It can also be used to
indicate how the form should initially be displayed. Choices are wsMinimized, wsMaximized,
and wsNormal.</P>
<P>
<H4>Runtime-Only Properties</H4>
<P>Some properties can be accessed only at runtime through code. The following are
the most commonly used runtime properties.</P>
<P><B>ActiveMDIChild&#160;&#160;</B>When read, the ActiveMDIChild property returns
a pointer to the currently active MDI child window. This property is read only. If
no MDI child is currently active or if the application is not an MDI application,
ActiveMDIChild returns nil.</P>
<P><B>Canvas&#160;&#160;</B>The form's canvas represents the drawing surface of the
form. The Canvas property gives you access to the form's canvas. By using the Canvas
property, you can draw bitmaps, lines, shapes, or text on the form at runtime. Most
of the time you will use a Label component to draw text on a form, an Image component
to display graphics, and a Shape component to draw shapes. However, there are times
when you need to draw on the canvas at runtime and the Canvas property enables you
to do that. The Canvas property can also be used to save an image of the form to
disk. Canvases are discussed in more detail on Day 12, &quot;Graphics and Multimedia
Programming.&quot;</P>
<P><B>ClientRect&#160;&#160;</B>The ClientRect property contains the top, left, right,
and bottom coordinates of the client area of the form. This is useful in a variety
of programming situations. For example, you might need to know the client area's
width and height in order to place a bitmap on the center of the form.</P>
<P><B>Handle&#160;&#160;</B>The Handle property returns the window handle (HWND)
of the form. Use this property when you need the window handle to pass to a Windows
API function.</P>
<P><B>ModalResult&#160;&#160;</B>The ModalResult property is used to indicate how
a modal form was closed. If you have a dialog box that has OK and Cancel buttons,
you can set ModalResult to mrOK when the user clicks the OK button and to mrCancel
when the user clicks the Cancel button. The calling form can then read ModalResult
to see which button was clicked to close the form. Other possibilities include mrYes,
mrNo, and mrAbort.</P>
<P><B>Owner&#160;&#160;</B>The Owner property is a pointer to the owner of the form.
The owner of the form is the object that is responsible for deleting the form when
the form is no longer needed. The parent of a component, on the other hand, is the
window (a form or another component) that acts as the container for the component.
In the case of a main form, the application object is both the owner of the form
and the parent of the form. In the case of components, the owner would be the form,
but the parent could be another component such as a panel.</P>
<P><B>Parent&#160;&#160;</B>The Parent property is a pointer to the parent of the
form. See the previous section about Owner for an explanation of Owner versus Parent.</P>
<P>
<H3><A NAME="Heading21"></A>Form Methods</H3>
<P>Forms are components, too. As such, forms have many methods in common with components.
Common methods include Show, ShowModal, and Invalidate, to name just a few. There
are some methods, however, that are specific to forms. As before, I'll discuss only
the most commonly used methods.</P>
<P>
<H4>BringToFront</H4>
<P>The B