ch15.htm

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	the TMultiply class declaration, just above the protected keyword:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>private
  FX : Integer;
  FY : Integer;</PRE>

</BLOCKQUOTE>

<PRE></PRE>

<DL>
	<DT></DT>
	<DD>These are the declarations for the data fields that will hold the X and Y property
	values.
	<P>
	<DT></DT>
	<DD><B>2. </B>Scroll down into the implementation section and locate the Get_X method
	(use the Code Explorer if you like). Type this line of code in the method:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>Result := FX;</PRE>

</BLOCKQUOTE>

<PRE></PRE>

<DL>
	<DT></DT>
	<DD><B>3. </B>Locate the Get_Y method and add this line:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>Result := FY;</PRE>

</BLOCKQUOTE>

<PRE></PRE>

<DL>
	<DT></DT>
	<DD><B>4. </B>Locate the DoIt method and add this line of code:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>Result := FX * FY;</PRE>

</BLOCKQUOTE>

<PRE></PRE>

<DL>
	<DT></DT>
	<DD>This line of code multiplies the value of FX and FY and returns the result.
	<P>
	<DT></DT>
	<DD><B>5. </B>Scroll down further until you see the Set_X method. Type this line
	of code in the Set_X method:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>FX := Value;</PRE>

</BLOCKQUOTE>

<PRE></PRE>

<DL>
	<DT></DT>
	<DD><B>6. </B>Locate the Set_Y method and add this line:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>FY := Value;</PRE>

</BLOCKQUOTE>

<PRE></PRE>
<P>That's all you need to do. Your code should now look like Listing 15.2.</P>
<P>
<H4>LISTING 15.2. THE COMPLETED MultiplyU UNIT.</H4>
<PRE>unit MultiplyU;
interface
uses
  Windows, ActiveX, ComObj, ComTest_TLB;
type
  TMultiply = class(TTypedComObject, IMultiply)
  private
    FX : Integer;
    FY : Integer;
  protected
    function DoIt: Integer; stdcall;
    function Get_X: Integer; stdcall;
    function Get_Y: Integer; stdcall;
    procedure Set_X(Value: Integer); stdcall;
    procedure Set_Y(Value: Integer); stdcall;
    {Declare IMultiply methods here}
  end;
implementation
uses ComServ;
function TMultiply.DoIt: Integer;
begin
  Result := FX * FY;
end; 
function TMultiply.Get_X: Integer;
begin
  Result := FX;
end;
function TMultiply.Get_Y: Integer;
begin
  Result := FY;
end;
procedure TMultiply.Set_X(Value: Integer);
begin
  FX := Value;
end;
</PRE>
<PRE>procedure TMultiply.Set_Y(Value: Integer);
</PRE>
<PRE>begin
  FY := Value;
end;
initialization
  TTypedComObjectFactory.Create(ComServer, TMultiply, Class_Multiply,
    ciMultiInstance, tmSingle);
end.
</PRE>
<P>Although you were working on the MulitplyU unit, Delphi was busy building the
type library and a unit to contain the type library code. The unit has the same name
as the project with a trailing _TLB. This project is named ComTest. The full unit
name for the type library unit, then, is ComTest_TLB.pas. Listing 15.3 shows this
unit as it exists at this point. Remember, your unit might not look exactly like
Listing 15.3.</P>
<P>
<H4>LISTING 15.3. THE ComTest_TLB.pas UNIT.</H4>
<PRE>unit ComTest_TLB;
// ******************************************************************** //
// WARNING                                                              //
// -------                                                              //
// The types declared in this file were generated from data read from a //
// Type Library. If this type library is explicitly or indirectly (via  //
// another type library referring to this type library) reimported, or  //
// the `Refresh' command of the Type Library Editor activated while   //
// editing the Type Library, the contents of this file will be        //
// regenerated and all manual modifications will be lost.               //
// ******************************************************************** //
// PASTLWTR : $Revision:   1.11.1.55  $
// File generated on 6/8/98 7:16:51 PM from Type Library described below.
// ******************************************************************** //
// Type Lib: D:\Borland\D4\Bin\ComTest.tlb
// IID\LCID: {7CDAFB76-FF36-11D1-81F1-0040052A83C4}\0
// Helpfile: 
// HelpString: ComTest Library
// Version:    1.0
// ******************************************************************** //
interface
uses Windows, ActiveX, Classes, Graphics, OleCtrls, StdVCL; 
// *********************************************************************//
// GUIDS declared in the TypeLibrary. Following prefixes are used:      //
//   Type Libraries     : LIBID_xxxx                                    //
//   CoClasses          : CLASS_xxxx                                    //
//   DISPInterfaces     : DIID_xxxx                                     //
//   Non-DISP interfaces: IID_xxxx                                      //
// *********************************************************************//
const
  LIBID_ComTest: TGUID = `{7CDAFB76-FF36-11D1-81F1-0040052A83C4}';
  IID_IMultiply: TGUID = `{7CDAFB77-FF36-11D1-81F1-0040052A83C4}';
  CLASS_Multiply: TGUID = `{7CDAFB79-FF36-11D1-81F1-0040052A83C4}';
type
// *********************************************************************//
// Forward declaration of interfaces defined in Type Library            //
// *********************************************************************//
  IMultiply = interface;
// *********************************************************************//
// Declaration of CoClasses defined in Type Library                     //
// (NOTE: Here we map each CoClass to its Default Interface)            //
// *********************************************************************//
  Multiply = IMultiply;
// *********************************************************************//
// Interface: IMultiply
// Flags:     (0)
// GUID:      {7CDAFB77-FF36-11D1-81F1-0040052A83C4}
// *********************************************************************//
  IMultiply = interface(IUnknown)
    [`{7CDAFB77-FF36-11D1-81F1-0040052A83C4}']
    function Get_X: Integer; stdcall;
    procedure Set_X(Value: Integer); stdcall;
    function Get_Y: Integer; stdcall;
    procedure Set_Y(Value: Integer); stdcall;
    function DoIt: Integer; stdcall;
  end;
  CoMultiply = class
    class function Create: IMultiply;
    class function CreateRemote(const MachineName: string): IMultiply;
  end;
implementation
uses ComObj;
</PRE>
<PRE>class function CoMultiply.Create: IMultiply;
</PRE>
<PRE>begin
  Result := CreateComObject(CLASS_Multiply) as IMultiply;
end;
class function CoMultiply.CreateRemote(const MachineName: string): &#194;IMultiply;
begin
  Result := CreateRemoteComObject(MachineName, CLASS_Multiply) as &#194;IMultiply;
end;
end.
</PRE>
<P>Notice that this unit contains the declaration for the IMultiply interface. As
you can see, IMultiply is derived from IUnknown. Notice also that this unit contains
the coclass Multiply.</P>
<P>It is important to understand that this unit is regenerated each time you compile
an ActiveX library project. It is generated from the type library file. Note the
warning at the top of the unit. The comments are telling you that any changes you
make to this file will be lost the next time the COM object is rebuilt. It really
doesn't do any good to modify the type library source file, because it will be regenerated
automatically.</P>
<P>
<H4>Building and Registering the COM Object</H4>
<P>Now you are ready to compile the ActiveX library project. This step compiles the
COM object and builds the DLL in which the COM object resides. After building the
COM object, you can register it. Here are the steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Choose Project|Build ComTest from the main menu. Delphi will build
	the DLL containing the COM object.
	<P>
	<DT></DT>
	<DD><B>2. </B>Choose Run|Register ActiveX Server from the main menu. This step registers
	the COM object with Windows. If you fail to perform this step, you will get an exception
	that says, &quot;Class not registered&quot; when you attempt to access the COM object.
	<P>
</DL>

<P>Delphi registers the COM object DLL with Windows. After the DLL has been registered,
Delphi displays a message box, as shown in Figure 15.4.</P>
<P><A HREF="javascript:popUp('28671504.gif')"><B>FIGURE 15.4.</B></A><B> </B><I>Delphi
reporting the COM object successfully registered.</I></P>

<P></P>

<P>When Windows registers the COM object, it adds information about the object to
the Registry. Figure 15.5 shows the Registry entry created when the COM object was
registered with Windows.</P>

<P><A HREF="javascript:popUp('28671505.gif')"><B>FIGURE 15.5.</B></A><B> </B><I>The
Registry key created when the COM object was registered.</I></P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> Delphi ships with a utility called TREGSVR.EXE that can be used to
	register an ActiveX control from the command line. To register a control called MYSTUFF.OCX,
	you would run TREGSVR from a command prompt like this: 
	<PRE>tregsvr mystuff.ocx</PRE>

</BLOCKQUOTE>

<PRE></PRE>


<BLOCKQUOTE>
	<P>To unregister an ActiveX, use the -u switch as follows: 
	<PRE>tregsvr -u mystuff.ocx</PRE>

</BLOCKQUOTE>

<PRE></PRE>


<BLOCKQUOTE>
	<P>Sometimes this is more convenient than loading an ActiveX project in Delphi and
	registering or unregistering the control from the IDE. 
<HR>
<BR>
	</P>

	<P>
<HR>
<strong>NOTE:</strong> In this exercise I had you create a COM object. You could also have
	used an automation object. An automation object derives from IDispatch rather than
	IUnknown. IDispatch provides the additional functionality required for a COM object
	to act as an automation server (an object that can control one application from another).
	
<HR>


</BLOCKQUOTE>

<P>Your COM object is now ready to use.</P>
<P>
<H4>Building an Application That Uses the COM Object</H4>
<P>A COM object doesn't do you much good if you can't use it. In this step, you create
an application that uses the COM object you just created. Follow these steps:</P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Create a new application. Place a Button component and a Label component
	on the form. Save the project as ComApp and the main form's unit as ComAppU.
	<P>
	<DT></DT>
	<DD><B>2. </B>Switch to the Code Editor and locate the uses list for the main unit.
	Add these units to the uses list:
	<P>
</DL>



<BLOCKQUOTE>
	<PRE>ComObj
ComTest_TLB</PRE>

</BLOCKQUOTE>

<PRE></PRE>

<DL>
	<DD>This ensures that the code that references the COM object will compile.
	<DT></DT>
	<DD><B>3. </B>Double-click the form's button to create an OnClick event handler.