ch15.htm

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	Modify the OnClick handler so that it looks like this:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>procedure TForm1.Button1Click(Sender: TObject);
var
  Mult : IMultiply;
  Res  : Integer;
begin
  Mult := CreateComObject(CLASS_Multiply) as IMultiply;
  if Assigned(Mult) then begin
    Mult.Set_X (20);
    Mult.Set_Y (60);
    Res := Mult.DoIt;
    Label1.Caption := IntToStr(Res);
  end;
end;</PRE>

</BLOCKQUOTE>

<PRE></PRE>
<P>This code first declares a pointer to the IMultiply interface called Mult and
an Integer variable to hold the result. Next, the CreateComObject function is called
with a parameter of CLASS_Multiply. CLASS_Multiply is a constant that contains the
GUID for the COM object class (refer to Listing 15.3).</P>
<P>The return value from CreateComObject is assigned to the Mult pointer. Notice
that I use the as operator to cast the return value to an IMultiply pointer. CreateComObject
returns an IUnknown pointer, so the as operator is used to cast the IUnknown pointer
to an IMultiply pointer.</P>
<P>After the COM object is created, I assign values to the X and Y properties. After
that I call the DoIt method of the COM object and display the result in the Label
component.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> In the real world, I would have written the preceding procedure differently.
	For example: 
	<PRE>procedure TForm1.Button1Click(Sender: TObject);
begin
  with CreateComObject(CLASS_Multiply) as IMultiply do begin
    Set_X(20);
    Set_Y(60);
    Label1.Caption := IntToStr(DoIt);
  end;
end;</PRE>

</BLOCKQUOTE>

<PRE></PRE>


<BLOCKQUOTE>
	<P>I wrote the procedure the way I did to illustrate each step. 
<HR>


</BLOCKQUOTE>

<P>Run the program. When you click the form's button, the label should change to
say &quot;1200&quot; (the product of 20 * 60). That's it! Your COM object works.
This COM object can be used from Visual Basic, Visual C++, C++Builder, or any other
development environment that supports COM.</P>
<P>
<H2><A NAME="Heading7"></A>Understanding ActiveX</H2>
<P><I>ActiveX</I> is a relatively new term for a technology that has been around
for awhile. Originally ActiveX controls were called <I>OCX controls</I>. The term
<I>OCX</I> is still widely used in some circles. An ActiveX control typically has
a filename extension of either DLL or OCX.</P>
<P>An ActiveX control is essentially a COM object in disguise. The primary difference
between an ActiveX control and a COM object is that an ActiveX control has a design-time
interface. An ActiveX control also has code that enables it to be deployed on a Web
page or over a network. ActiveX is a subset of COM, so everything you learned about
COM objects in the first part of the chapter applies to ActiveX controls as well.</P>
<P>
<H3><A NAME="Heading8"></A>Using Third-Party ActiveX Controls</H3>
<P>There isn't a lot to know about installing and using third-party ActiveX controls.
All you have to do is import the ActiveX into the IDE and begin using the control.
To see how this works, let's do a quick exercise. This exercise requires that you
have Microsoft Internet Explorer installed on your system. If you don't have Internet
Explorer installed, skip this exercise. (You won't be missing anything because I
show you how to install an ActiveX control you have built in the section &quot;Build,
Register, and Install the Control.&quot;) Perform these steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Choose Component|Import ActiveX Control from the main menu. The Import
	ActiveX dialog box is displayed.
	<P>
	<DT></DT>
	<DD><B>2. </B>Scroll down through the list of installed components until you find
	Microsoft Internet Controls (the exact text of the item will depend on the version
	of Internet Explorer you have installed on your system). Select the item. Figure
	15.6 shows the Import ActiveX dialog box after this step.
	<P>
</DL>

<P><A HREF="javascript:popUp('28671506.gif')"><B>FIGURE 15.6.</B></A><B> </B><I>The
Import ActiveX dialog box.</I></P>

<DL>
	<DT><I></I></DT>
	<DD>Notice the Class names list box in the middle of the page. This list box contains
	a list of ActiveX controls in the selected file (SHDOCVW.DLL in this case).
	<P>
	<DT></DT>
	<DD><B>3. </B>The Palette page field shows ActiveX. This is a the palette page where
	the new controls will be installed. Click on this field and type ActiveXTest.
	<P>
	<DT></DT>
	<DD><B>4. </B>Leave the Unit dir name and Search path fields on their default settings
	and click the Install button. The Install dialog box comes up and asks what package
	you want the controls installed into. (All controls, whether they are VCL or ActiveX,
	must be in a package.)
	<P>
	<DT></DT>
	<DD><B>5. </B>Click on the Into new package tab. Enter MSIE in the File name field
	and Internet Explorer Package in the Description field.
	<P>
	<DT></DT>
	<DD><B>6. </B>Click the OK button. Delphi creates a new package called MSIE.dpk and
	prompts you to build and install the package. Click Yes to install the package. After
	the package is built, Delphi displays a message box telling you which controls were
	added to the Component palette. Click Yes to dismiss the message box.
	<P>
	<DT></DT>
	<DD><B>7. </B>Scroll the Component palette to find the ActiveXText tab. You should
	see two or three controls on that page of the Component palette (again, depending
	on the version of Internet Explorer you have installed). The components are ready
	for use.
	<P>
</DL>

<P>Experiment with the new controls and see how they work. You probably won't get
very far without documentation, but at least you get a sense for how installing an
ActiveX works. (For a more complete explanation of using Internet Explorer as an
ActiveX, see the section, &quot;Using Internet Explorer as an ActiveX Control&quot;
on the Bonus Day, &quot;Building Internet Applications.&quot;)</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> You must have a design-time license in order to use an installed
	ActiveX control. A design-time license is a file with an .LIC extension. In some
	cases you can import ActiveX controls to the Delphi Component palette without a design-time
	license, but you will get an error message when you attempt to place the control
	on your form. 
<HR>


</BLOCKQUOTE>

<P>To remove the Internet Explorer controls from the Component palette, choose Component|Install
Packages from the main menu. Locate the Internet Explorer Package in the Design packages
list box and click the Remove button. The ActiveXTest tab is removed from the Component
palette.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> Deploying an application that uses ActiveX controls requires special
	attention. Deploying applications using ActiveX controls is covered in detail on
	the Bonus Day in the section &quot;Deploying Internet Applications.&quot; 
<HR>


</BLOCKQUOTE>

<H3><A NAME="Heading9"></A>Creating New ActiveX Controls</H3>
<P>There are two ways to create an ActiveX control in Delphi:</P>

<UL>
	<LI>From an existing VCL component
	<P>
	<LI>From scratch using an ActiveForm
</UL>

<P>In this section, you create an ActiveX control using both of these methods.</P>
<P>
<H4>Creating an ActiveX Control from an Existing VCL Component</H4>
<P>Creating an ActiveX control from an existing VCL component is downright simple.
After you create a component, you can turn it into an ActiveX control in no time
at all. I haven't talked about creating components yet, so I don't want to go into
a lot of detail on creating components now (covered on Day 20, &quot;Creating Components&quot;).
What you will do, then, is create an ActiveX control from one of the VCL components
provided by Borland.</P>
<P><B>Generate the ActiveX Project with the ActiveX Control Wizard</B></P>
<P>The first step is to generate the ActiveX project. As always, Delphi does most
of the work for you. All you have to do is supply a few fields in the ActiveX Control
Wizard. Here are the steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Choose File|Close All to close all projects and then choose File|New
	from the main menu. The Object Repository is displayed.
	<P>
	<DT></DT>
	<DD><B>2. </B>Click the ActiveX page and then double-click the ActiveX Control icon.
	The ActiveX Control Wizard is displayed (see Figure 15.7).
	<P>
</DL>

<P><A HREF="javascript:popUp('28671507.gif')"><B>FIGURE 15.7.</B></A><B> </B><I>The
ActiveX Control Wizard.</I></P>

<DL>
	<DT><I></I></DT>
	<DD><B>3. </B>Select TButton from the list of classes in the VCL Class Name combo
	box. The next four fields are automatically filled in with default values. Because
	this is just a test, you can leave those fields on their default values. The fields
	are self-explanatory, so I don't need to go over each one.
	<P>
	<DT></DT>
	<DD><B>4. </B>The Threading Model is set to Apartment. Leave this setting as it is.
	Other threading models include Single, Free, and Both. See the Delphi help for more
	information on threading models.
	<P>
	<DT></DT>
	<DD><B>5. </B>Check the Include Design-Time License check box. When this option is
	checked, Delphi will create a design-time license for the control. The design-time
	license will prevent other programmers from using the control unless they have the
	license.
	<P>
	<DT></DT>
	<DD><B>6. </B>Check the Include Version Information check box. This will enable you
	to add version info to the control via the Project Options dialog box.
	<P>
	<DT></DT>
	<DD><B>7. </B>Check the Include About Box check box as well. When this box is checked,
	Delphi will automatically create an About dialog box for the control. Click OK to
	close the ActiveX Control Wizard.
	<P>
</DL>

<P>Delphi will create a project file (ButtonXControl1.bpr) and three units for the
project. The first unit is the TButtonX class unit (ButtonXImp1.pas). The second
unit is the type library file for the control, named ButtonXControl1_TLB.pas. This
file contains the information Delphi needs to create the type library for the control.
The third file, About1.pas, is the unit for the About box. If you want to customize
the About box, you can do that at this time. The About box is just another Delphi
form, so feel free to customize it in any way you like.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> Version info is required in order for your ActiveX controls to work
	in Visual Basic. 
<HR>


</BLOCKQUOTE>

<P><B>Build, Register, and Install the Control</B></P>
<P>Because you aren't making any modifications to the control itself, you can jump
right to building the control and registering it. This is the same process you went
through when you registered the COM object you created earlier. An extra step is
required when implementing ActiveX controls, though, because ActiveX controls have
a design-time interface. Try this:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Choose Project|Build ButtonXControl1 from the main menu. Delphi builds
	the ActiveX project.
	<P>
	<DT></DT>
	<DD><B>2. </B>Choose Run|Register ActiveX Server from the main menu. The ActiveX
	control is registered and Delphi displays a message box telling you that the OCX
	is registered (ActiveX projects have a default extension of .OCX). Click OK to dismiss
	the message box.
	<P>
	<DT></DT>
	<DD><B>3. </B>Choose Component|Import ActiveX Control from the main menu. Choose
	ButtonXControl1 Library (Version 1.0) from the list of installed controls (had you
	not performed step 2, this entry would not have been present in the list of installed
	controls). The class name of the button, TButtonX, shows in the Class names list
	box.
	<P>
	<DT></DT>
	<DD><B>4. </B>Set the Palette page field to ActiveX. Click Install to continue.
	<P>
	<DT></DT>
	<DD><B>5. </B>The Install dialog box is displayed. You are going to install the control
	into the default Delphi user package DCLUSR40.BPL. The File name field should already
	contain this package. If it doesn't, choose it from the combo box. The Description
	field now says Delphi User's Components. Click the OK button to install the control.
	<P>
	<DT></DT>
	<DD><B>6. </B>Click Yes to the message box regarding building and installing DCLUSR40.BPL.
	Click OK when the message box confirming the installation is displayed. The control
	is now installed.
	<P>
</DL>

<P><B>Test the ActiveX Control</B></P>
<P>Now you can test your new ActiveX control. First, create a new project.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> When you create a new project, Delphi will prompt you to save the
	package file (DCLUSR40.DPK) and the ActiveX control project. Whether you save these
	files is up to you. My intention was to have you create a quick ActiveX. There's
	really no need to save the files. If, however, you think you might want to save the
	files to examine them later, save the files. 
<HR>


</BLOCKQUOTE>

<P>Now follow these steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Locate the ActiveX tab on the Component palette.
	<P>
	<DT></DT>
	<DD><B>2. </B>The last control in the list is the ButtonX control. Select it.
	<P>
	<DT></DT>
	<DD><B>3. </B>Place a ButtonX control on your form. Notice that the button doesn't
	have a default caption as a regular VCL button does.
	<P>
	<DT></DT>
	<DD><B>4. </B>Change the Caption property to Test. The button's caption changes just
	as a VCL button's caption would change.
	<P>
	<DT></DT>
	<DD>Notice the list of properties in the Object Inspector. They are mostly the same
	properties you would see on a VCL button (the ActiveX was created from a VCL TButton
	after all), but you might have noticed that the Value column looks slightly different.
	Remember, this is an ActiveX control and is intended to be used in any environment
	that hosts ActiveX controls. For that reason, some of the property values are expressed
	in a more generic way.
	<P>
	<DT></DT>