Creating and Registering the Component

Creation of every component begins the same way: create a unit, derive a component class, register it, compile it, and install it on the Tool palette. This process is outlined in Creating a new component.

For this example, follow the general procedure for creating a component, with these specifics:

Call the component's unit AboutDlg.
Derive a new component type called TAboutBoxDlg, descended from TComponent.
Register TAboutBoxDlg on the Samples page of the Tool palette.

The resulting unit should look like this:

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unit AboutDlg;
interface
uses
  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls, Forms;
type
  TAboutBoxDlg = class(TComponent)
  end;
procedure Register;
implementation
procedure Register;
begin
  RegisterComponents('Samples', [TAboutBoxDlg]);
end;
end.

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#include <vcl\vcl.h>
#pragma hdrstop
#include "AboutDlg.h"
//---------------------------------------------------------------------------
#pragma package(smart_init);
//---------------------------------------------------------------------------
static inline TAboutBoxDlg *ValidCtrCheck()
{
  return new TAboutBoxDlg(NULL);
}
//---------------------------------------------------------------------------
namespace AboutDlg {
{
  void __fastcall PACKAGE Register()
  {
    TComponentClass classes[1] = {__classid(TAboutBoxDlg)};
    RegisterComponents("Samples", classes, 0);
  }
}

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#ifndef AboutDlgH
#define AboutDlgH
//---------------------------------------------------------------------------
#include <vcl\sysutils.hpp>
#include <vcl\controls.hpp>
#include <vcl\classes.hpp>
#include <vcl\forms.hpp>
//---------------------------------------------------------------------------
class PACKAGE TAboutBoxDlg : public TComponent
{
private:
protected:
public:
__published:
};
//---------------------------------------------------------------------------
#endif

The new component now has only the capabilities built into TComponent. It is the simplest nonvisual component. In the next section, you will create the interface between the component and the dialog box.

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